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fmicb-13-979383 September 8, 2022 Time: 16:15 # 1
TYPE Review
PUBLISHED 14 September 2022
DOI 10.3389/fmicb.2022.979383
OPEN ACCESS
EDITED BY
Pankaj Bhatt,
Purdue University, United States
REVIEWED BY
Sikandar I. Mulla,
REVA University, India
Geeta Bhandari,
Swami Rama Himalayan University,
India
*CORRESPONDENCE
Yongyue Lu
luyongyue@scau.edu.cn
SPECIALTY SECTION
This article was submitted to
Terrestrial Microbiology,
a section of the journal
Frontiers in Microbiology
RECEIVED 27 June 2022
ACCEPTED 19 August 2022
PUBLISHED 14 September 2022
CITATION
Jaffar S, Ahmad S and Lu Y (2022)
Contribution of insect gut microbiota
and their associated enzymes in insect
physiology and biodegradation
of pesticides.
Front. Microbiol. 13:979383.
doi: 10.3389/fmicb.2022.979383
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does not comply with these terms.
Contribution of insect gut
microbiota and their associated
enzymes in insect physiology
and biodegradation of
pesticides
Saleem Jaffar1, Sajjad Ahmad2,3 and Yongyue Lu1*
1Department of Entomology, South China Agricultural University, Guangzhou, China, 2Key
Laboratory of Integrated Pest Management of Crop in South China, Ministry of Agriculture
and Rural Affairs, South China Agricultural University, Guangzhou, China, 3Key Laboratory of Natural
Pesticide and Chemical Biology, Ministry of Education, South China Agricultural University,
Guangzhou, China
Synthetic pesticides are extensively and injudiciously applied to control
agriculture and household pests worldwide. Due to their high use, their
toxic residues have enormously increased in the agroecosystem in the
past several years. They have caused many severe threats to non-target
organisms, including humans. Therefore, the complete removal of toxic
compounds is gaining wide attention to protect the ecosystem and the
diversity of living organisms. Several methods, such as physical, chemical
and biological, are applied to degrade compounds, but as compared to
other methods, biological methods are considered more efficient, fast,
eco-friendly and less expensive. In particular, employing microbial species
and their purified enzymes makes the degradation of toxic pollutants
more accessible and converts them into non-toxic products by several
metabolic pathways. The digestive tract of insects is usually known as
a superior organ that provides a nutrient-rich environment to hundreds
of microbial species that perform a pivotal role in various physiological
and ecological functions. There is a direct relationship between pesticides
and insect pests: pesticides reduce the growth of insect species and
alter the phyla located in the gut microbiome. In comparison, the insect
gut microbiota tries to degrade toxic compounds by changing their
toxicity, increasing the production and regulation of a diverse range of
enzymes. These enzymes breakdown into their derivatives, and microbial
species utilize them as a sole source of carbon, sulfur and energy.
The resistance of pesticides (carbamates, pyrethroids, organophosphates,
organochlorines, and neonicotinoids) in insect species is developed by
metabolic mechanisms, regulation of enzymes and the expression of various
microbial detoxifying genes in insect guts. This review summarizes the
toxic effects of agrochemicals on humans, animals, birds and beneficial
arthropods. It explores the preferential role of insect gut microbial species in
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the degradation process and the resistance mechanism of several pesticides
in insect species. Additionally, various metabolic pathways have been
systematically discussed to better understand the degradation of xenobiotics
by insect gut microbial species.
KEYWORDS
symbiotic microbes, enzymes, pesticides, non-target organisms, metabolic pathways
Introduction
In modern agriculture, for the management of various kinds
of pests and the production of high-yield crops to meet the
food availability for human beings, pesticides are extensively
applied all over the world (Giambò et al.,2021). Pesticides
are chemicals that control different pests such as rodents,
arthropods, weeds and microbial pathogens (Huang and Chen,
2022). Pest management strategy is a vigorous arms race: on the
one hand, farmers, pesticide inventors, agribusiness men, and
researchers throughout the world struggle for the protection of
crops and their higher production (Damalas and Koutroubas,
2018). While on the other hand, insects and other microbial
pathogens follow their biological metabolism and drive to
live and reproduce their generations (Pietri and Liang,2018).
Due to the repetitive application of pesticides with higher
concentrations, insects and other pathogens fail to control them
and develop cross-resistance (Daisley et al.,2018;Gressel,2018).
However, insect resistance against insecticides produces severely
threaten non-target living organisms and contaminates the
ecosystem (Khalid et al.,2021). Various studies have reported
that pesticides’ toxic residues are abundantly present in soil,
sediments, and water bodies (Mulla, Ameen et al.,2020).
These hazardous compounds and their toxic metabolite
residues significantly affect the climate and living organisms
such as soil biota, fish, birds, mammals, plants and human
beings (Lee et al.,2021;Pujar et al.,2022). In addition, their
toxic residues ruin organisms’ behavior, reproduction cycles
and metabolism mechanisms, which can permanently alter
the interrelated ecosystem (Zhao et al.,2019). These toxic
compounds are degraded into simpler or less toxic substances
using various methods such as chemical reactions, physical
methods, photodegradation and biodegradation. Compared
to other techniques, biological methods are less expensive,
environment-friendly, more effective and easier to adapt to
remove emerging pollutants (Hao et al.,2018).
Microbial species have been extensively applied for
the biodegradation of environmental pollutants, including
agrochemicals (Chen et al.,2015). To date, researchers
throughout the world have screened millions of microbial
species (bacteria, fungi, yeasts, algae, etc.) from the soil,
sewage sludge, wastewater and other contaminated sites (Yang
L. et al.,2021). Investigation of pure cultures of microbial
species has revealed that toxic molecules are transformed into
various metabolites (Ahlawat et al.,2020). Nevertheless, due to
considering prominent features of insect gut microbial species
like high resistance to pesticides and purification of novel
suitable enzymes, various researchers have isolated a diverse
number of microbial species for the biological treatment of
wastewater and clean-up of the contaminated environment
(Skidmore and Hansen,2017).
Gut microbial species play a pivotal role in the
detoxification, mineralization, and catabolism of organic
molecules employed in pest control as determined by
degradation or histochemical mechanisms (Berasategui
et al.,2016). They are also considered superior organs for
producing pheromones, synthesizing vitamins, and different
enzymes to prevent pathogens (Ozdal et al.,2016). The gut
of insects and other arthropods provides a rich nutrient
medium for developing microbial species that can produce
some essential enzymes and contribute significantly to insect
physiology (Ramakrishnan et al.,2019;Figure 1). Insect gut
microflora provides a prominent environment for transforming
genes, mutant traits, and conjugative plasmids, which can adapt
to harsh environmental conditions and perform smoothly in
biodegradation processes (Xia et al.,2018).
More importantly, microbial species isolated from this
source are rarely indigenous to the polluted environment.
Hence, their use in bioaugmentation and biodegradation
enhances their efficiency to remove environmental pollutants
(Kadri et al.,2018). To keep in mind these critical points,
insect associated-microbial species, especially bacteria, are more
vigorous and beneficial because they are interrelated with
the application of active ingredients (Blanton and Peterson,
2020). The coordination between symbiotic microbial species
and resistance to pesticides in arthropods would provide
new opportunities for managing pests and isolating efficient
microbial species to protect the agroecosystem (Li et al.,2018).
This review investigates the resistance mechanisms of
different pesticides in insect pathogens and the transforming
mechanisms of their parent toxic compounds into less toxic
intermediates by the isolation of gut microflora. Additionally,
microbial species interlinked with insects and involved in the
detoxification of pesticides will be essential in the designing of
future novel ingredients to ensure their long-term efficiency.
Therefore, investigating the linkages between environmental
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FIGURE 1
Role of insect gut microbiota in insect physiology.
contaminants and gut microflora is of great significance. This
literature review will be beneficial and guider to reveal the
possible impacts of gut microflora on the fate of organic
pollutants and provide a more comprehensive insight into
the mineralization, transformation, and biodegradation of
pesticides and other emerging pollutants from the environment.
Fate of pesticides in the
environment
Throughout the world, an extensive range of pesticides like
insecticides, herbicides, rodenticides, fungicides, nematicides,
molluscicides, rodenticides, bactericides, repellents, insect
growth regulators and disinfectants have been generated for the
management of specific target pests in agriculture, aquaculture,
horticulture and households (van de Merwe et al.,2018).
Currently, more than 3.5 million tons of pesticides are used
throughout the world, out of which 47.5% are herbicides,
29.5% are insecticides, 17.5% are fungicides, and 5.5% are
other types of pesticides (Sharma et al.,2019). Since its
inception 50 years ago, China has grown to be the world’s
largest producer and consumer of pesticides. The other major
pesticide-consuming countries are the United States, Argentina,
Thailand, Brazil, Italy, France, Canada, Japan, and India
(Olisah et al.,2019). These agrochemicals are extensively
introduced into modern agriculture and urban ecosystems
during their production, transportation, improper storage and
unwise applications, which cause severe environmental threats
(Ahmad et al.,2021). Local governments and environmental
protection agencies regulate the production of pesticides and
their applications. But the ecological management and risk
assessment rules and regulations are generally restricted to
formulating agrochemicals and their active ingredients and
additives (Pokhrel et al.,2018). According to a combined
statement of WHO and UNEP, approximately 200,000 people
worldwide die, and roughly three million are affected yearly by
pesticide residues (Meftaul et al.,2020). Another study revealed
that the majority of cases, nearly 95% of them are reported
from developing countries (Yadav et al.,2015). Agrochemicals
severely effect the ecosystem through toxic residues at the
application sites, such as agricultural farms, lawns and parks
(Wu et al.,2007). However, these compounds pose severe threats
to aquatic organisms by leaching down into the groundwater
and through surface runoff into lakes, rivers, and other water
bodies (Ahmad et al.,2022a). Furthermore, when pesticides are
applied to crops, horticulture areas, home lawns and school
parks, many people including, children and women, animals,
beneficial arthropods, birds and wildlife creatures, are seriously
affected (Masud et al.,2018).
Due to unwise applications of pesticides with higher
concentrations, their toxic residues have been frequently
revealed in the urban air, dust, soil and water bodies than in
those of rural areas, predominantly due to primary, secondary
and re-emissions of the parent compound and their toxic
derivatives (Ren et al.,2018). Agronomic crops and other
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ornamental plants can easily absorb these chemicals from
contaminated sites and transfer them to their vegetative and
reproductive parts (Kim et al.,2017). When farmers apply
higher concentrations of pesticides to protect their crops
from pests and diseases, their residues are entered into food
commodities (Dai et al.,2010). However, various researchers
are working to investigate toxic pesticide residues in fruits
and vegetables growing in agricultural, rural and urban areas
in developing and developed countries (Pietrzak et al.,2020;
Barbieri et al.,2021;Zamule et al.,2021). Incorporating pesticide
residues into daily food consumption is a foremost safety
issue for consumers worldwide (Hasan et al.,2017). The
excessive use of pesticides deliberately affects flora, fauna and
the ecosystem (Arunkumar et al.,2017). We briefly discuss the
risk of pesticides to humans’ health and other non-target living
organisms in the following sections.
Human health
The labors working in pesticide formulation industries,
agriculture areas, and assassinators for managing household
pests are generally affected by direct or indirect pesticide
exposure. There are higher chances of risk for people working
in the pesticide manufacturing industries at the time of
formulation, packaging and production because they handle
crude materials and other hazardous solvents (Gangemi et al.,
2016;Nicolopoulou-Stamati et al.,2016). Various kinds of
health disorders such as cancer, diabetes problems, respiratory
issues, neurological disorders, reproductive syndromes and
oxidative stress are produced due to direct or indirect exposure
and handling of pesticides or their toxic active ingredients
in foodstuffs (Carles et al.,2017;Grewal,2017;Rani et al.,
2021). Some studies have revealed that due to continuous risk
assessment of highly toxic compounds, including pesticides
such as lung cancer, breast cancer, leukemia and multiple
myeloma have occurred in human beings (Han et al.,2018;
Ruiz et al.,2018;Huang et al.,2019;Jaacks et al.,2019). Meng
et al. (2016) carried out a study to investigate agrochemical
exposure in indoor dust and blood samples. Results of this
study revealed asthma is positively interlinked with exposure to
alpha-hexachlorocyclohexane in humans.
In another study to evaluate pesticide exposure and its
effects on human health, Tanner et al. (2009) carried out a study.
They discovered that Parkinson’s disease and 2-4 D herbicides
are closely associated with their cause. Yan et al. (2016) reported
that pesticides and Alzheimer’s disease are closely interlinked,
and a meta-analysis proved that pesticide exposure is hazardous
for the brain and eyes. Recently, Shah et al. (2020) carried out a
study investigating the effect of organochlorine pesticides such
as β-hexachlorocyclohexane, dichlorodiphenyldichloroethylene
and dieldrin on human epithelial ovary cells for the risk
prediction of ovarian cancer. The findings of this study
revealed that organochlorine pesticides highly affect human
health and stimulate the measurement of reactive oxygen
species (ROS), pro-inflammatory response and DNA damage in
human epithelial ovary cells. Besides this, DDT organochlorine
pesticide caused DNA damage, genetic instability, micronucleus
formation and the sister chromatid exchange in humans (Yáñez
et al.,2004;Savant et al.,2018). Cassidy et al. (2005) studied
the relationship between women’s breast cancer and heptachlor
pesticide. The results of this study revealed that women’s
breast cancer risk was positively correlated with the level
of heptachlor epoxide. Richardson et al. (2014) investigated
the effect of dichlorodiphenyltrichloroethane (DDT) and
dichlorodiphenyldichloroethylene (DDE) on human health and
found that these both pesticides were responsible for causing
Alzheimer’s disease. In another study, due to high exposure to
organochlorine pesticides their toxic effects on human health
were examined, and it was found that these pesticides cause
Parkinson’s disease (Freire and Koifman,2012).
Impacts on water bodies
Imprudent application of pesticides in farming could pollute
surface water via draining, runoff, leaching and drift. Polluted
surface water harms non-target organisms, including humans
and animals (Chrustek et al.,2018;Lee and Choi,2020).
Surface water is considered a major drinking water source
in developing nations such as Pakistan, India, Bangladesh,
Nepal, and Sri Lanka (Mojiri et al.,2020;Teklu et al.,
2022). The residues of various pesticides from the groups of
organochlorines, organophosphate, carbamates, neonicotinoids,
and pyrethroids are found in the rivers of California (Anderson
et al.,2018). Besides this, several other European countries
also investigated pesticide residues and noticed that 76 types of
pesticide residues are present in European soil. Furthermore, it
was revealed that 83% of soil contained one type of residue, and
58% of soil contained two, three or more types of residues. The
highest concentrations of glyphosate and its derivatives were
detected frequently. The presence of pesticide residues in the
surface water and rivers all over the world causes critical threats
to aquatic organisms (Mitchell et al.,2017;Tian et al.,2018;Dias
et al.,2020).
A study was conducted to evaluate the exposure of
organochlorine and pyrethroid pesticide residues in surface
water, fish, sediments and aquatic weeds in the southern region.
Results of this study revealed that residues of organochlorine
pesticides were identified in surface water, sediments, fish
muscle, gills, liver, and aquatic weeds at a concentration of
0.001–34.44 µg/L, 0.01–16.72 µg/Kg, 0.01–26.05 µg/Kg, 0.01–
40.56 µg/Kg, 0.01–65.14 µg/Kg, 0.01–5.53 µg/Kg, respectively.
This study further explained that organochlorine pesticides such
as eldrin, dieldrin, endosulfan, endrin, and heptachlor were
the prominent pesticides identified with the above level of
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maximum residue limit set by the World Health Organization
in surface water, sediments and fish (Arisekar et al.,2019). In
another study, residues of pesticides in the Guayas River at
181 places were investigated using the solid phase extraction
method. Results of this study explained that 26 types of
pesticide residues in fresh water at 108 sampling sites (60%)
were detected with higher concentrations. The major types
of pesticides found in river water are cadusafos, butachlor,
and pendimethalin at 62, 21, and 21, with concentrations
of 0.081, 2.006, and 0.557 µg/L, respectively. Finally, this
study also demonstrated that all detected pesticides in river
water are frequently found in agriculture and horticulture
crops such as rice and banana, with higher concentrations
due to irregular application methods like aerial spraying.
Finally, their residues are transferred to the rice field
and river water. This study also suggested that precaution
measures such as legal regulations and awareness campaigns
for farmers and local industries are highly recommended
to control environmental contamination and prevent the
accumulation of pesticide residues in aquatic and terrestrial
systems (Deknock et al.,2019).
Recently, for the investigation of highly used herbicide
residues such as atrazine, acetochlor, alachlor, hexazinone,
metolachlor, simazine, terbuthylazine, trifluralin, and phenoxy
acids (MCPA and 2,4-D) in two type of fishes (Clarias
gariepinus,Oreochromis mossambicus) an experimental study
was conducted. This study showed that all herbicides’ residues
were found in analyzed samples with a total concentration
ranging from 42.3 to 238 ng/g in Clarias gariepinus and 72.2–
291 ng/g in Oreochromis mossambicus. The most dominant
herbicides which are found in fish tissues, gills and liver are
phenoxy acid herbicides, acetochlor, atrazine and terbuthylazine
with the ranges of 17.6 ±12 ng/g, 28.9 ±16 ng/g,
15.4 ±5.8 ng/g, 12.7 ±7.1 ng/g, 12.4 ±12 ng/g, respectively
(Tyohemba et al.,2021).
Threats to beneficial arthropods
Insect pollinators and predators play a pivotal role in
developing many crops, as insect pollinators increase the yield
and predators protect crops from pest infestation (Ihara et al.,
2017). But due to excessive use of agrochemicals and unselective
treatment in the modern agriculture system, their diversity
and abundance are severely affected (Joshi et al.,2020). It has
been reported that only 1% of pesticides reach the target site,
whereas the remaining amount accumulates in the environment
and contaminates it (Goergen et al.,2016;Fine et al.,2017;
Stein et al.,2017). Beneficial arthropods are directly linked with
pesticide exposure at the time of application or immediately
after applying pesticides. The droplets of toxic residues could
inlet on their cuticle by ingestion and influence their growth and
mating behavior (Sgolastra et al.,2017).
Abraham et al. (2018) investigated the effects of glyphosate
herbicides on beneficial insects (Apis mellifera, Hypotrigona
ruspolii) under laboratory conditions. The bees were treated
with the recommended concentration, a two-fold higher
recommended concentration, and distilled water for control.
The impact of glyphosate herbicide was compared with the
lambda cyhalothrin. The herbicide was sprayed on plants as
well as the bees were treated with herbicide-sprayed filter paper.
Results of this study revealed that a more significant number of
bees died after contact with the herbicide in both ways. This
study concluded that spraying glyphosate herbicide was very
dangerous for beneficial insects by contacting or spraying on
fresh plants with more than the recommended dose. Another
study investigated the effects of widely used neonicotinoids
(acetamiprid, imidacloprid, thiamethoxam, and thiacloprid)
on spiders. All the neonicotinoids with recommended doses
were applied in field conditions, and short-term exposure
was evaluated on spiders. Results of this study revealed that
after 1 h, imidacloprid showed more critical effects and
revealed partial acute lethality (15–32%). Acetamiprid showed
strong sublethal effects, particularly when employed dorsally on
Philodromus cespitum. After 1 day of application of thiacloprid
and acetamiprid, Linyphiidae species were paralyzed or finally
caused death, especially in males (Øezáè et al.,2019).
A study was conducted to reveal the toxicity of imidacloprid,
thiamethoxam and sulfoxaflor on the aphid (Aphis gossypii).
The impact of these pesticides on natural enemies of aphids,
especially parasitoids (Aphidius colemani), was investigated with
low lethal, median lethal and sublethal concentrations. This
study showed that the median lethal concentration caused
maximum mortality of parasitoids compared to sulfoxaflor,
while imidacloprid had the least negligible impact on the
diversity of parasitoids (Ricupero et al.,2020). To study the
effects of more neonicotinoid pesticides such as imidacloprid,
thiamethoxam, clothianidin and dinotefuran on the parasitoid
larvae (Coccinella septempunctata) by the application of lethal
and median lethal doses using the direct contact method. This
study indicated that neonicotinoid pesticides are hazardous
for the survival of larvae. The median lethal dose highly
impacts the emergence of larval instars, pupal emergence and
weight. Finally, this study concluded that pesticide application
is hazardous for the survival of beneficial insects, primarily
involved in integrated pest management services (Wu et al.,
2021).
Toxic effects on plants and animals
Every day, increasing environmental pollution affects many
living organisms and has always been considered a critical
challenge in the scientific community (Niroumand et al.,2016).
The high accumulation of pesticides in agricultural soils and
their cumulative behavior and toxicity pose severe threats to
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beneficial plants (Ferrando and Matamoros,2020). It is well
known that the accumulation of pesticides affects the behavior
of soil microbial species and enzymes and is absorbed by plants,
which further transfers it to non-target organisms through the
food chain process (Sayed et al.,2020). The adaptation of
medicinal plants to cure various diseases has been practiced for
several centuries and even today plays a pivotal role in primary
health care as a therapeutic agent in several developing nations
(Reinholds et al.,2017;Kumar et al.,2018).
The application of herbal medicines to treat various illnesses
has increased significantly in the past few decades due to their
prominent features such as minimum side effects compared
to synthetic drugs, inexpensive and excellent viability (Ammar
et al.,2020). Besides their numerous benefits, toxic pesticide
residues could be more dangerous and cause many diseases in
humans and other living organisms (Righi et al.,2018). Recently,
Luo et al. (2021) have studied the accumulation of pesticide
residuals in various medicinal plants, which are frequently used
throughout the world for the welfare of humanity. Results of this
study explained that in 1771 samples, 88% of pesticide residues
were detected. Terrifyingly, 59% of pesticide residues are beyond
the European Pharmacopoeia (EP) limit and 43% are confined
to 35 types of banned pesticides worldwide. Additionally, this
study demonstrated that eight pesticide residues were five
hundred times higher than the default maximum residue limit
set by the environmental protection agency.
In another study, Li R. -X. et al. (2020) investigated the
presence of various pesticide residues in herbal plants using
the Quick Easy Cheap Effective Rugged Safe (QuEChERS)
extraction method. All residues were detected through
Ultra-Performance Liquid Chromatography and Gas
Chromatography-Mass spectrometry analysis. This method
was applied to 39 real samples of Ophiopogon japonicus,
Polygonatum odoratum, and Paeonia suffruticosa obtained
from different locations, and the results of this study revealed
that in 92.3% of samples, residues of pesticides were detected.
This study showed that 26% pesticide residues are frequently
detected in three traditional Chinese medicine plants. In
addition, tebuconazole and paclobutrazol residue levels were
considerably higher in nine samples compared to the maximum
residue limit.
The primary way of transformation of pesticides in the
general population is the consumption of food commodities
that might be polluted with toxic residues of pesticides (Nagy
et al.,2020). However, their residues can ultimately be inserted
into animals’ digestive tracts via various pathways and affect
their physical conditions (Altun et al.,2017;Yuan et al.,
2019). Recently, Nerozzi et al. (2020) investigated the effects
of glyphosate and its most famous formulation Roundup,
on animal health and reproductive functions. In this study,
the pig was chosen as a model animal. The commercial
semen of pigs was treated with glyphosate and Roundup
formulation at 0–360 µg/mL concentrations and incubated at
38◦C for 3 h. The consequences of this study indicated that the
application of high concentrations of glyphosate significantly
reduced sperm viability, motility, mitochondrial activity and
acrosome integrity. While on the other side, by treating lower
concentrations (5–100 µg/mL) of Roundup formulation, all the
disorders were observed after 1 h of incubation. Finally, this
study concluded that pesticides active ingredients and inert
materials negatively affect animals and the human reproductive
system. Jarrell et al. (2020) also reported that glyphosate-based
herbicides are more dangerous for animals’ health and cause
severe diseases such as the reproductive system, altering the
regulation of enzymes, disrupting serum levels and activity, and
loss of fertility.
An investigation was carried out to evaluate deltamethrin
and ivermectin residues on local sheep milk and meat. A total of
eighty samples (40 each for milk and meat) were obtained from
different places, and detection of pesticide residues was observed
by performing High-Performance Liquid Chromatography.
Results of this study indicated that 92.5 of milk samples and 90%
of meat samples were polluted with toxic deltamethrin residues.
More alarmingly, this study highlighted that all samples were
contaminated with ivermectin residues above the maximum
residue limit set by the World Health Organization (WHO) and
Food and Agriculture Organization (FAO) (Mani and Al Araji,
2022).
However, to remove various environmental pollutants,
protect the diversity of living organisms, and save crops from
pests, effective, eco-friendly, less expensive, and more applicable
methods are urgently required.
System biology-based approaches
for the pesticides degradation in
agroecosystem
In order to gain a better knowledge of plants and microbes,
researchers are using system biology technologies (Bhatt et al.,
2016). Numerous details on the interactions between microbes,
plants, humans and other non-target organisms by pesticides
in nature have been fabricated because of advances in the
fields of genomics and proteomics (Bhandari et al.,2021).
Recently, a biological system-based approach was carried out to
remove atrazine residues from the contaminated environment
and to understand the complex biological network with
different cellular systems modeling and simulation of atrazine
were performed. The findings of this study revealed that
two functional enzymes from bacteria (chlorohydrolase and
monooxygenase) actively performed and completely degraded
atrazine from the environment. To learn more about the
biochemistry and physiology of atrazine in various cellular
networks, additional analysis and simulations of the utilized
model were performed. Atrazine degradation’s 289 nodes and
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300 edges were verified by topological analysis (Bhatt et al.,
2020). Insecticides containing pyrethroids are frequently used
to control pests in homes and agricultural crops (Bhatt et al.,
2022b). The complete removal of various pyrethroid pesticides
was achieved using a system biological based approach and a
simulated model. Results of this study explain that the toxic
metabolites of pyrethroids severely affect non-target organisms,
especially beneficial arthropods, microorganisms and human
health. In addition, this investigation actively contributed to
analyzing the toxicity and removal of other emerging pollutants
from the agroecosystem (Bhatt et al.,2021a). In another study, a
potential bacterial strain, Bacillus subtilis 1D, was isolated from
a polluted agriculture field and investigated their degradation
efficiency to degrade cypermethrin from the environment. The
findings of this study showed that bacterial stain efficiently
degraded 95% of cypermethrin within 15 days and converted
it into various metabolites. In addition, laccase and esterase
enzymes were identified from bacterial strain and observed
that both enzymes more rapidly degraded cypermethrin as
compared to free cells (Gangola et al.,2018).
A biological molecular model and a purified methyl
transferase enzyme were adopted to degrade residues of methyl
halide from a polluted environment. This study explained that
the enzymes played a crucial role in the remediation of methyl
halide. In addition, this model demonstrates that a volatile
poisonous substance impacts the earth’s environmental layers
and life systems (Bhatt et al.,2019). A potential Bacillus sp. FA3
was isolated from the contaminated environment and examined
their degradation efficiency using the Box-Behnken design to
degrade fipronil from the soil and water systems. Results of
this study revealed that at optimum conditions (temperature
of 32◦C, pH 7, and rotational speed of 110 rpm), the bacterial
strain performed efficiently and degraded 76% of fipronil within
15 days. Finally, this study concluded that Bacillus sp. FA3 was
a superior candidate for removing fipronil from the wastewater
and soil system and could be helpful for large-scale treatment
(Bhatt et al.,2021b).
Diversification of symbiotic
microbiota and their role in insect
physiology
A diverse range of symbiotic microbial species have been
produced within the insect gut and have contributed a very
significant role in the regulation of insect metabolism, enhanced
food digestion, increased excretion of waste fluids, protecting
the host from enemies, developing resistance against toxins and
degrading them into their intermediates (Smith et al.,2017;
Heys et al.,2018;Tokuda et al.,2018;Hauffe and Barelli,2019;
Figure 1). The identification and characterization of insect gut
microbial species are investigated mainly by culture-dependent
or culture-independent techniques (Bourguignon et al.,2018;
Bruno et al.,2019). However, the culture-dependent method
usually produces biased results. It relies on various parameters
and techniques, while in the culture-independent method, a lot
of omics and molecular approaches are applied, such as 16S
rRNA and BLAST analysis, which provide a better and more
comprehensive picture of the microbial communities located
in insect guts (Eski et al.,2018;Erlandson et al.,2019;Erb
and Kliebenstein,2020). The application of high throughput
and next-generation sequencing provides new insights into
obtaining microbial ecology (Harishankar et al.,2013). It reveals
that the diversity of microbial species by using independent
culture methods identified a higher number of microbial
communities than traditional culture-based and conventional
molecular methods (Bhatt et al.,2021c,a,2022a;Mishra et al.,
2021;Ahmad et al.,2022a). Therefore, a comprehensive
evaluation of microbial communities within a host species
plays a vital role in understanding insect physiology and their
interactions with insect hosts (Armitage et al.,2022).
A comprehensive investigation was carried out to evaluate
insect symbiotic microbial species and their significant roles
in 305 insect samples belonging to 218 insect species in
21 taxonomic orders. Using an independent culture method
and adopting 16S rRNA analysis, 454 pyrosequencing were
performed, and 174,374 sequence reads were gained. This
study’s results indicated a total of 9301 bacterial operational
taxonomic units (OTUs) at a distance level of 3% from all
samples, with an average of 84.3% ( ±97.7) OTUs per sample.
In addition, this study suggested that gut microbial species
were dominated by Proteobacteria, Wolbachia, and Firmicutes
with a ratio of 62.1, 14.1, and 20.7%, respectively. Finally, this
study concluded that these bacterial communities could help in
food digestion, the development of larval stages and enhanced
the insect immune system (Yun et al.,2014). The findings of
another study showed that the hindgut of subterranean termites
contained a 90% population of bacteria and archaea (Hongoh,
2010). The diversity of bacterial species in the digestive tract
of fruit flies (Drosophila melanogaster) was studied using 454
pyrosequencing of 16S rRNA gene amplicons. Results of this
investigation explained that 5 OTUs enriched the sequence
reads, and ≤97% of that sequence identity could be related
to Acetobacter pomorum,Acetobacter tropicalis,Lactobacillus
brevis,Lactobacillus fructivorans, and Lactobacillus plantarum
(Wong et al.,2011).
In another study, using an independent culture technique
and adopting molecular approaches such as denaturing gradient
gel electrophoreses and 16S rRNA analysis, a high diversity of
genus Gammaproteobacteria were identified in the gut of the
locust Schistocerca gregaria. The results of this study suggested
that this diversity of bacterial species engaged with a defensive
mechanism and enhanced it against external pathogens and
toxic chemicals (Dillon et al.,2010). Recently, Xue et al. (2021)
investigated the diversity of gut microbial species in various life
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TABLE 1 Pesticide resistance cases in various insects mediated by gut microbial species.
Name of
pesticide
Insect common
name
Insect scientific
name
Gut microbiota References
Prothiofos Diamondback moth Plutella xylostella Pseudomonas sp., Stenotrophomonas sp., Acinetobacter sp., and
Serratia marcescens.
Indiragandhi et al.,2007
Tebuconazole Brown planthopper Nilaparvata lugens Acinetobacter sp. Song et al.,2021
DDT Diamondback moth Plutella xylostella Bacillus thuringiensis and Saccharopolyspora spinosa Sarfraz and Keddie,2005
Imidacloprid Honeybee
Fruit fly
Fruit fly
Whitefly
Bed bug
Apis mellifera
Bactrocera tau
Drosophila
melanogaster
Bemisia tabaci
Cimex hemipterus
Bifidobacterium sp., Lactobacillus sp., Klebstella oxytoca,
Pantoea agglomerans, Staphylococcus sp.
Lactobacillus sp., Rickettsia sp., Frischella sp. Wolbachia sp.,
Yersinia sp., Bacillus sp., and Acetobacter sp.
Kontsedalov et al.,2008;
Prabhakar et al.,2008;
Chmiel et al.,2019;
Rouzé et al.,2019;
Alberoni et al.,2021;Soh
and Veera Singham,2022
Atrazine Jewel wasp Nasonia vitripennis Serratia marcescens and Pseudomonas protegens Wang G. -H. et al.,2020
Chlorpyriphos Diamondback moth Plutella xylostella Enterobacteriales sp., Vibrionales sp., Pseudomonadales sp.,
Xanthomonadales sp., and Lactobacillales sp.
Xia et al.,2013
Fipronil Diamondback moth
Honeybee
Plutella xylostella
Apis mellifera
Enterobacteriales sp., Vibrionales sp., Pseudomonadales sp.,
Xanthomonadales sp., Lactobacillales sp., Bifidobacterium sp.,
Alphaproteobacteria sp., Gammaproteobacteria sp., and
Lactobacillus sp.
Xia et al.,2013;Rouzé
et al.,2019;Paris et al.,
2020
Pyraclostrobin Honeybee Apis mellifera Gilliamella sp. and Lactobacillus sp. DeGrandi-Hoffman
et al.,2017
Abamectin Parasitic wasps Eretmocerus
mundus,
Eretmocerus
eremicus, and
Encarsia formosa
Arthrobacter sp. Fernández et al.,2019
Thiamethoxam Whitefly
Honeybee
Bemisia tabaci
Apis mellifera
Delftia sp., Rickettsia sp.,
Bifidobacterium sp., Lactobacillus sp.
Alphaproteobacteria sp., and Gammaproteobacteria sp.
Kontsedalov et al.,2008;
Xie et al.,2012;Rouzé
et al.,2019;Paris et al.,
2020
Deltamethrin Diamondback moth
Mosquitos
Cotton aphid
Plutella xylostella
Anopheles albimanus
Aphis gossypii
Enterococcus mundtii, Carnobacterium maltaromaticum,
Bacillus sp., Buchner sp., Pseudomonas sp.,
Pantoea agglomerans and Pseudomonas fragi
Li et al.,2017;Dada et al.,
2019;Shang et al.,2021b
Coumaphos Honeybee Apis mellifera Bifidobacterium sp. and Lactobacillus sp. Rouzé et al.,2019
Malathion Fruit fly Bactrocera tau Klebstella oxytoca, Pantoea agglomerans, and Staphylococcus sp. Prabhakar et al.,2008
Cypermethrin Tobacco cutworm or
cotton leafworm
Spodoptera litura Clostridium botulinum, Clostridium butyricum, and
Pseudomonas putida
Karthi et al.,2020
Phoxim Silkworm Bombyx mori Enterobacter cloacae, Staphylococcus sp., Methylobacterium sp.,
and Aurantimonadaceae sp.
Li F. et al.,2020
Beta-cypermethrin Cockroach Blattella germanica Lactobacillus sp., Metarhizium anisopliae, Parabacteroides sp.,
Lachnoclostridium sp., and Tyzzerella sp.
Zhang and Yang,2019;
Zhang J. et al.,2022
Carboxamide Honeybee Apis mellifera Alphaproteobacteria sp. and Gammaproteobacteria sp. Paris et al.,2020
Phosphine Red flour beetle Tribolium castaneum Bacillus subtilis, Staphylococcus sp., saprophyticus sp.,
Enterobacter sp., Lysinibacillus fusiformis, Klebsiella pneumonia,
and Achromobacter sp.
Gowda et al.,2021
Trichlorphon Oriental fruit fly Bactrocera dorsalis Citrobacter freundii Guo et al.,2017
Endosulfan Fruit fly Bactrocera tau Klebstella oxytoca, Pantoea agglomerans, and Staphylococcus sp. Prabhakar et al.,2008
Temephos Asian malaria
mosquito
Anopheles stephensi Pseudomonas sp., Aeromonas sp., Exiguobacterium sp., and
Microbacterium sp.
Soltani et al.,2017
Permethrin Mosquitos
African malaria
mosquito
Anopheles albimanus
Anopheles gambiae
Pantoea agglomerans and Pseudomonas fragi.
Sphingobacterium, Lysinibacillus and Streptococcus
Dada et al.,2019
Omoke et al.,2021
Alphacypermethrin Mosquitos Anopheles albimanus Pantoea agglomerans and Pseudomonas fragi Dada et al.,2019
Thiacloprid Honeybee Apis mellifera Enterococcus faecalis, Snodgrassella alvi, Bartonella apis, Dickel et al.,2018;
(Continued)
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TABLE 1 (Continued)
Name of
pesticide
Insect common
name
Insect scientific
name
Gut microbiota References
Frischella perrara, Lactobacillus kunkeei, Frischella sp.,
Bifidobacterium asteroids, and Gilliamella apicola
Alberoni et al.,2021;
Cuesta-Maté et al.,2021
Fenitrothion Bean bug Riptortus pedestris Burkholderia sp. Itoh et al.,2018
Pyriproxyfen Silkworm
Whitefly
Bombyx mori
Bemisia tabaci
Burkholderia sp., Rhizobia sp., Rickettsia sp., Caulobacter sp.,
Sphingobacteria sp., and Enterobacteria sp.
Kontsedalov et al.,2008;
Lu et al.,2022
Chlorpyriphos Diamondback moth Plutella xylostella Enterococcus sp., Enterobacter sp., and Serratia sp. Gurr et al.,2018
Acetamiprid Honeybee
Whitefly
Apis mellifera
Bemisia tabaci
Snodgrassella alvi, Bartonella apis, Frischella perrara,
Lactobacillus kunkeei, Bifidobacterium asteroids, Gilliamella
apicola, and Rickettsia sp.
Kontsedalov et al.,2008;
Cuesta-Maté et al.,2021
Spinosyns Diamondback moth Plutella xylostella Bacillus thuringiensis and Saccharopolyspora spinosa Sarfraz and Keddie,2005
Pendimethalin Ground beetle Pterostichus melas Enterobacter sp., Pseudomonas sp., Pantoea sp., and Paracoccus
sp.
Giglio et al.,2021
Sulfoxaflor Cotton aphid Aphis gossypii Buchner sp. and Arsenophonus sp. Shang et al.,2021b
Avermectin Gypsy moth Lymantria dispar
asiatica
Weissella sp., Lactobacillus sp., Pseudomonas sp., Candida sp.,
Tausonia sp., Chaetomium sp., Diutina sp., and Alternaria sp.
Zeng et al.,2020
Buprofezin Small brown
planthopper
Laodelphax
striatellus
Wolbachia sp. and Rickettsia sp. Li et al.,2018
Boscalid Honeybee Apis mellifera Gilliamella sp. and Lactobacillus sp. DeGrandi-Hoffman
et al.,2017
Carbaryl Fall armyworm Spodoptera
frugiperda
Bacillus thuringiensis and Varimorpha necatrix Fuxa and Richter,1990
Methyl parathion Fall armyworm Spodoptera
frugiperda
Bacillus thuringiensis and Varimorpha necatrix Fuxa and Richter,1990
Spiromesifen Whitefly Bemisia tabaci Rickettsia sp. Kontsedalov et al.,2008
Glyphosate Colorado potato
beetle
Leptinotarsa
decemlineata
Agrobacterium sp., Ochrobactrum sp., Rhodobacter sp.,
Rhizobium sp., and Acidovorax sp.
Gómez-Gallego et al.,
2020
Guadipyr Silkworm Bombyx mori Pseudomonas sp. and Curvibacter sp. Hou et al.,2021
Lufenuron Formosan
subterranean termite
Coptotermes
formosanus
Pseudomonas aeruginosa, Serratia marcescens, and Bacillus
thuringiensis
Wang et al.,2013
Fenitrothion Bed bug Cimex hemipterus Wolbachia sp., Yersinia sp., and Bacillus sp. Soh and Veera Singham,
2022
Spiromesifen Whitefly Bemisia tabaci Rickettsia sp. Kontsedalov et al.,2008
stages of Adelphocoris suturalis by adopting the independent
culture technique. Results of this study explained that the gut
of the first and second instar was highly accomplished with the
diversity of bacterial species. This study demonstrated that in
the phylum, Proteobacteria and Firmicutes were dominant with
a ratio of 87.06 and 9.43%, respectively, while at the genus level,
Erwinia (28.98%), Staphylococcus (5.69%), and Acinetobacter
(4.54%) were dominant bacteria. Finally, this study concluded
that the diversity of bacterial species could be applied for
biological control.
Functions of insect gut microbiota
The insect gut is divided into three primary regions: the
anterior midgut or foregut, the posterior midgut, and the
hindgut (Wang G. -H. et al.,2020). The anterior midgut and
hindgut arise from the embryonic epithelium. They are sheltered
from pathogens by an exoskeleton of chitin and integument
glycoproteins, while the posterior midgut is mainly used for
absorption and digestion (He et al.,2018). Additionally, the
hindgut of insects serves as an extension of the body cavity
and is used to collect dietary waste (Siddiqui et al.,2022).
However, it offers an appropriate environment that stimulates
the proliferation and diversification of insect gut microbiomes
(Bruno et al.,2019). Many studies have reported that insect
gut microbiota plays a significant role in developing symbiotic
insect interactions facilitated by secondary metabolites (Shang
et al.,2021a). Besides this, they also play an essential role in the
detoxification of pesticides, providing a natural defense system,
nutrient availability, development of resistance against toxins
and pathogens, breakdown of food, and suitable for proper
growth of insects (Jang and Kikuchi,2020;Jing et al.,2020;
Mogren and Shikano,2021;Tilottama et al.,2021).
High benefits and more prominent features of insect gut
microbial species provide new insights into the development of
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beneficial arthropods, which are often used as biocontrol agents
to solve environmental problems and further applications for
the welfare of humans (Samoilova et al.,2016;Borrelli et al.,
2017;Liao et al.,2017). However, considering the superior
features of insect gut microbiota, this review mainly focuses on
their potential applications for the detoxification of pesticides
and their toxic metabolites for the cleanup of the environment
(Wang S. et al.,2020).
Development of resistance against
pesticides
Pesticides have been applied to manage pests and diseases
since the start of agriculture for the production and protection
of crops. However, the unwise use of pesticides accumulates in
the ecosystem and contaminates plants, air, water and soil (Lewis
et al.,2016). The storage of pesticides in plants can develop
resistance or tolerance against various pests (Ramakrishnan
et al.,2019). A lot of studies have demonstrated that resistance
is also developed due to reduction of toxicity of a compound,
the introduction of a new pesticide group, target site mutation
or over expression, pre-date or wrong selection of pesticide,
repetition of the same chemical, environmental changes, and
degradation of parent compounds into their metabolites by
insect gut microbiota and their detoxifying enzymes (Naik et al.,
2018;Hawkins et al.,2019;Matsuda et al.,2020;Table 1).
Insect digestive systems have a robust defensive system
mainly equipped with various microbial species such as
bacteria, fungi, archaea, and protozoa (Chen et al.,2021).
In a recent study, the isolation of various microbial species
in the digestive tract of worker honeybees (Apis mellifera).
Results of this study demonstrated that nine species of
bacteria from various genera were isolated; five belonged to
Snodgrassella alvi,Gilliamella apicola, two species were from
Lactobacillus, and one from Bifidobacterium (Douglas,2018).
Various microbial communities allow insects to tolerate or reject
toxic compounds through various metabolic processes and
develop a peritrophic medium composed of chitin microfibrils
and a protein-carbohydrate medium (Kamalakkannan et al.,
2017;Rumbos et al.,2018). This peritrophic medium plays a
pivotal role in the development of resistance against chemicals
due to some prominent features such as releasing digestive
enzymes, availability of nutrients and providing protection to
epithelial cells from external microbes and toxins through a
semipermeable membrane (Puri et al.,2022;Siddiqui et al.,
2022). These physiological obstacles between the lumen and
epithelium actively contribute to the defense mechanism and
minimize the activation of pesticides on the host rather than
reducing microbial load in the gut (Chen et al.,2022;Figure 2).
Recently, a laboratory experiment was conducted to
investigate organophosphate pesticide resistance in a serious
rice pest, Cletus punctiger by the gut symbiont. Results of
this study demonstrated that a rice bug effectively degraded
FIGURE 2
Schematic diagram of isolation of insect gut microbial species and their functions in biodegradation of environmental pollutants.
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organophosphate fenitrothion by Burkholderia bacterial specie
via oral infection and stayed it in the midgut part of the rice
bug. The degradation of fenitrothion by the isolating bacterial
species from the midgut revealed that gut microbiomes are
highly capable of degrading pesticides in insects, and insect
gut symbiosis plays a significant role in the development of
resistance against fenitrothion in the host rice bug (Ishigami
et al.,2021). In another study, the resistance of stored grain
products against phosphine fumigation was studied. Four
major stored grain pests (Rhyzopertha dominica,Sitophilus
granaries, Tribolium castaneum, and Trogoderma granarium)
were reared under laboratory conditions for up to seven
generations. Results of this study indicated that insect gut
symbiosis develops resistance in all pests. Regarding their
level of resistance, Rhyzopertha dominica was highly resistant
followed by Tribolium castaneum, Trogoderma granarium,
and Sitophilus granaries. Although this study concluded that
phosphine tablets are excessively applied to manage stored
products and are considered very efficient against various stored
grain pests, the development of resistance may lead to a serious
failure of their applications (Wakil et al.,2021).
An investigation was carried out to study the role of gut
microbiota in developing resistance against various insecticides
in the laboratory and open field conditions in the larvae of
Spodoptera frugiperda. The insect pests were collected from
various corn fields in five Brazilian states. In a metagenomic
experiment and 16S rRNA analysis, the isolation of bacterial
species from insect gut in the selective medium was achieved.
The maximum growth of microbial species in insecticides was
observed, and it was found that all microbes utilized it as a sole
source of carbon and energy. This study indicated that bacteria
isolated from field larvae grew better and degraded insecticides
more efficiently than those collected from laboratory-selected
strains. However, this study concluded that due to the high
efficiency and diversity of insect gut microbes in the field, larval
insects are more capable of degrading pesticides and showed
high resistance (Gomes et al.,2020).
A study was conducted to evaluate the resistance of
chlorpyriphos in diamondback moths (Plutella xylostella) by
insect gut microbiota. In this investigation, three bacterial
species from insect guts such as Enterococcus sp., Enterobacter
sp., and Serratia sp. were isolated and examined for their
role in detoxifying chlorpyriphos and developing resistance
in diamondback moths. Results of this study indicated that
Enterococcus sp. increased resistance against the most widely
used insecticide, chlorpyriphos. At the same time, Serratia
sp. reduced resistance in the diamondback moth and for
Enterobacter sp. no effect was observed. In addition, this study
explained that Enterococcus sp., vitamin C and acetylsalicylic
acid increased the regulation of antimicrobial peptides, which
played a crucial role in the development of insecticide resistance
(Xia et al.,2018). In another study, Wang et al. (2021)
explained that insect gut microbial species play a significant
role in insecticide deltamethrin resistance in Aedes albopictus.
Additionally, experimental results indicated that by full-length
16S rRNA analysis, two bacterial species were collected from
insect guts such as Serratia oryzae and Acinetobacter junii
and investigated their growth in six kinds of growth media
in biotic and abiotic conditions. Further, they observed that
both symbiotic bacteria are mainly facultative in an anaerobic
environment. Moreover, this study explained that insect
symbiotic bacterial species actively promoted insect resistance
against insect pesticides.
Molecular mechanism of resistance
against pesticides by insect gut
microbiota
To identify the complete profile and total biodiversity of
microbial communities in insect gut microbiota and polluted
sites, modern molecular biological approaches including
clone libraries, probes, reverse sample genome probing,
fluorescence in situ hybridization, community profiling or DNA
fingerprinting, next-generation sequencing and pyrosequencing
provide a more significant explanation as compared to the
conventional biological tools (Ahmad et al.,2022b). Various
functional parts of an insect’s gut microbes, such as enzymes
and genes, are responsible for developing pesticide resistance
in insects (Bhatt et al.,2022b). Metagenomic analysis was
performed to identify major microbial species in the gut
of a honeybee (Apis mellifera) and their functional roles in
developing resistance. This study’s results revealed that insect
gut microbe gene contents (Gilliamella apicola) are related
to various host-dependent symbiotic functions. Moreover, as
evidenced by the case of pectin breakdown by G. apicola,
genetic variations are related to functional variations. The
glycoside hydrolase and polysaccharide lyase enzyme families
discovered in the honeybee metagenome are depicted with their
respective cleavage sites on the schematic of the pectin molecule
(Engel and Moran,2013). In another study, an investigation
of gut microbial species from three diamondback moth larvae
was carried out to study prothiofos resistance. Findings from
16S rRNA showed that the bacterial community from the
prothiofos-resistant larval gut was more diversified. In addition,
the secretion of chitinase enzymes from the population of
insect gut bacteria significantly contributed to host antagonism
against entomopathogens and nutrition (Indiragandhi et al.,
2007). Pesticide-resistance cockroach species such as German
cockroaches, American cockroaches, and Oriental cockroaches
are rich sources of insect gut microbiota and play a crucial
role in insect physiology (Zhang X. C. et al.,2022). For
example, the effect of beta-cypermethrin resistance development
in cockroaches (Blattella germanica) by the gut microbial
population and their genetic association with host growth
was investigated. Results of 16S rRNA gene sequencing and
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metagenomics indicated that Lactobacillus spp. were abundantly
present in the foregut and midgut of cockroaches. In addition,
carbohydrate-active enzymes actively contribute to developing
resistance, insect growth, and fitness (Zhang and Yang,2019).
However, modern molecular biological tools efficiently describe
the microbial interaction with the host and external pathogens.
Moreover, in the future, these approaches could be applied
to using and managing environmental bioprocesses through
knowledge-based control.
Role of gut microbiota for
biodegradation of pesticides
In many insect species, resistance to pesticides has been
confirmed. It has been found that they are very beneficial
for degrading toxic compounds due to their digesting abilities
(Schmidt and Engel,2021). The degradation of pesticides
depends on various factors such as microbial remediation
and the chemical hydrolysis process, which are additionally
correlated with many physiological properties such as pH,
temperature, organic matter, and moisture content (Bhatt
et al.,2022b). However, the insect gut provides a favorable
environment for developing diverse microbial communities.
Hence, they efficiently deliver many promising facilities to
their host (Shan et al.,2021). Symbiotic microbial species
isolated from insect gut can perform in extreme environmental
conditions to degrade pesticides and other emerging pollutants
(Francis and Aneesh,2022;Figure 3).
Recently, Wang et al. (2022) investigated the degradation
of various pesticides by isolating microbial species from stored
grain pests and studied the resistance mechanism. In this
experiment, from multiple locations, adults of different stored
grain pests (Sitophilus oryzae,Cryptolestes ferrugineus, and
Rhyzopertha dominica) were collected and isolated as five
bacterial species. Results of this study indicated that all screened
bacterial species could degrade deltamethrin, malathion, and
pirimiphos-methyl efficiently and use their residues as a source
of carbon and energy, which are favorable for their growth.
Additionally, this study revealed that when bacterial species are
treated with 0.5–10 mg/kg of malathion, pirimiphos-methyl,
and 0.3–0.75 mg/kg of deltamethrin, gnotobiotic reinoculation
and their survival rates in the host are significantly increased,
which implies that development of insecticide resistance highly
depends on concentration rate. Moreover, this study also
explained that the in vitro biodegradation of pesticides through
gut bacteria was not entirely consistent with their in vivo
operation in host pesticide resistance, which suggested that
instead of direct degradation of pesticides, other physiological
and morphological processes are also responsible for pesticide
tolerance or resistance.
In another study, insects of Orthoptera and Dermaptera
were collected from various sites. Fourteen bacterial species
were isolated for the biodegradation of deltamethrin from a
FIGURE 3
Graphical representation of gut microbes’ development of resistance against pesticides.
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polluted environment. All the bacterial species were analyzed
by 16SRNA and identified as Poecilimon tauricola,Locusta
migratoria,Gryllus bimaculatus,Forficula Auricularia,
Pseudomonas aeruginosa,Stenotrophomonas maltophilia,
Bacillus atrophaeus,Acinetobacter lwoffii,Rhodococcus
coprophilus,Brevundimonas vesicularis,Pseudomonas syringae,
Yersinia frederiksenii,Bacillus licheniformis,Enterobacter
intermedius, and Serratia marcescen. In addition, this study
explained that eleven of them were gram-negative bacteria,
and three were gram-positive bacteria, potentially deleting
deltamethrin up to 100 mg/L. This study concluded that
insecticide-tolerated gut microbiota is enriched with nutrients
and is considered a powerful tool for the remediation of various
kinds of pollutants from the ecosystem (Özdal and Algur,
2020). An indigenous rod-shaped gram-negative bacterium was
isolated from the digestive tract of a grasshopper (Poecilimon
tauricola) for the potential biodegradation of α-endosulfan
and α-cypermethrin. By morphological, physiological, and 16S
rRNA sequence analysis, the bacterial strain was characterized as
Acinetobacter schindler and named B7. This study demonstrated
that when the bacterial strain was treated with 100 mg/L of both
pesticides in a glucose-mediated non-sulfur medium, significant
growth of the bacterial strain was observed. Additionally, this
study showed that within 10 days, the bacterial strain was
capable of degrading 67.31 and 68.4% of α-endosulfan and
α-cypermethrin, respectively (Ozdal and Algur,2022).
Organophosphates are an influential group of pesticides
that are excessively applied to control insect pest infestations
across several agricultural and horticultural crops. The residues
of this group are very toxic to the environment and
spread many diseases to non-target organisms. Therefore,
it is essential to remove their residues from the ecosystem
by a potential degradation method. Recently, a study was
conducted on the effective biodegradation of organophosphate
pesticides, chlorpyriphos and polyethylene, by isolating insect
gut microbial species. This study isolated four potential
bacterial species: Bacillus licheniformis,Pseudomonas cereus,
Pseudomonas putida, and Bacillus subtilis, from the gut
of the citrus mealybug (Planococcus citri). Results of this
study revealed that all symbiotic bacterial species utilized
chlorpyriphos and polyethylene as a sole source of carbon
and energy and enhanced their growth and enzymatic activity.
Findings of the degradation experiment showed that after the
treatment of 45 days, a satisfactory reduction of polyethylene
weight was noticed, and scanning electron microscope analysis
suggested that a biofilm formation around the polyethylene
sheet by bacterial isolates was also observed. While in the
case of chlorpyriphos, results indicated that after 21 days,
significant degradation was observed in soil and water. In
addition, this study revealed that Pseudomonas cereus and
Pseudomonas putida have more potential to degrade both
pollutants in diverse environmental conditions (Ibrahim et al.,
2021).
To degrade clothianidin residues in an open environment,
seven bacterial species such as Edwardsiella sp., two Serratia sp.,
Rahnella sp., Pantoea sp., Hafnia sp., and Enterobacter sp. were
isolated from the digestive tract of the honeybee. To examine
the growth of all bacterial strains, they were treated with various
concentrations of clothianidin as a sole source of carbon and
energy. They found that all bacterial strains provide satisfactory
growth up to 10 ppb of clothianidin. Results of the degradation
experiment showed that within 3 days, all endogenous bacterial
strains noticed complete degradation of clothianidin (El Khoury
et al.,2022).
For the biodegradation of multi-pesticides such as
chlorpyriphos, cypermethrin, malathion, quinalphos, and
triazophos, 13 indigenous microbial species were isolated from
the gut of the cotton bollworm (Helicoverpa armigera) and
tested for their degradation efficiency. After physiochemical,
morphological and 16S rRNA sequence analysis, all bacterial
strains were identified as Bacillus pumillis CL1, Enterococcus
casseliflavus CL2, Bacillus subtilis CL3, Rhodococcus sp. CL4,
Pseudomonas sp. CL5, Staphylococcus sp. CL6, Pseudomonas
aeruginosa CL7, Proteus vulgaris HL1, Cellulosimicrobium
cellulans HL2, Klebsiella oxytoca HL3, Bacillus subtilis HL4,
Stenotrophomonas maltophilla HL5, and Pseudomonas sp.
HL6. Results of this study indicated that strains CL2 and CL4
provided more rapid growth in the presence of malathion and
chlorpyriphos in a mineral salt medium. Gas chromatography
and mass spectrometry analysis revealed that strain CL4 has
the potential to degrade 44% of chlorpyriphos and strain
CL2 was capable to degrade 26% of chlorpyriphos and
57.1% of malathion in mineral salt medium (Madhusudhan
et al.,2021). In another study, a symbiotic gut bacterium,
Citrobacter sp. (CF-BD), was isolated from the digestive tract
of tephritid fruit flies (Bactrocera dorsalis) and investigated
their degradation efficiency against trichlorphon insecticide.
Results of this study showed that insect gut microbiota
plays a vital role in developing resistance against toxin
chemicals and efficiently degrade trichlorphon into metabolites.
This study also explains that various hydrolase genes were
identified in the bacterial isolate CF-BD. In the presence of
trichlorphon, the maximum gene expression was observed,
and it was found that these critical genes play a crucial role
in developing resistance in tephritid fruit flies (Cheng et al.,
2017).
Screening of gut microbial enzymes for
biodegradation of pesticides
In the insect body system, various potential natural
enzymes are linked with different biological processes and
play a vital role in toxic detoxifying substances in target sites
(Lin et al.,2015;Naik et al.,2018;Bhandari et al.,2021).
Based on some previous reports, it is found that resistance or
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TABLE 2 Functions of insect enzymes in detoxification of pesticides and insect physiology.
Insect common
name
Insect scientific
name
Name of
pesticide
Name of enzyme Functions Reference
Spongy moth Lymantria dispar Methidathion Superoxide dismutase,
catalase, glutathione
peroxidase
Develop defense mechanism and
protect from oxidative stress
Aslanturk et al.,2011
Fall armyworm Spodoptera
frugiperda
Organophosphate
insecticides
Alkaline phosphatase,
esterase, glutathione
S-transferase,
aminopeptidase, and
proteinase
Resistance, detoxification of
pesticides
Zhu et al.,2015
Parasitic wasps Eretmocerus
mundus,
Eretmocerus
eremicus and
Encarsia formosa
Abamectin Esterases Resistance, support to gut
microbes, play key role in insect
biology, ecology and behavior
Fernández et al.,
2019
Colombian
mosquito
Aedes aegypti Pyrethroid
insecticides
Esterases and oxidases Resistance and mutation
development
Granada et al.,2021
Whitefly Bemisia tabaci Neonicotinoid
insecticides
Cytochrome P450 Insecticide resistance, support to
symbiotic bacteria
Barman et al.,2021
Honeybee Apis mellifera Flumethrin Catalase Resistance, increased immunity
to pathogens and improvement of
detoxification genes (GST,
Hymenoptaecin, Defensin1,
Catalase, GAPDH)
Yu et al.,2021
Greater Wax Moth Galleria mellonella Malathion Esterase and glutathione
S-transferase
Resistance, detoxification of
malathion and development of
complex biological products
Serebrov et al.,2006
Yellow fever
mosquito
Aedes aegypti Permethrin Cytochrome P450
monooxygenases
Insecticide resistance, perform
multiple biological functions and
metabolize pesticide
Somwang et al.,
2011;David et al.,
2014
Yellow fever
mosquito
Aedes aegypti Deltamethrin Cytochrome P450 Metabolic resistance Faucon et al.,2015
Diamondback moth Plutella xylostella Fenvalerate, fipronil,
flufenoxuron and
monocrotophos
Hydrolases, transferases and
oxygenase’s
Detoxification of pesticides and
resistance development
Mohan and Gujar,
2003
Yellow fever
mosquito
Aedes aegypti Glyphosate and
alpha pyrene
Cytochrome P450
monooxygenases, glutathione
S-transferases and
carboxy/cholinesterase
Resistance, improvement of
detoxification genes and
development of biological
products
Riaz et al.,2009
Brown planthopper Nilaparvata lugens Acephate,
thiamethoxam and
buprofezin
Esterases, glutathione
S-transferases and
mixed-function oxidases
Resistance Malathi et al.,2017
Housefly Musca domestica Diazinon Cytochrome P450 Resistance and role in insect
biology, ecology, and behavior
Cariño et al.,1994
African malaria
mosquito
Anopheles gambiae Bendiocarb Cytochrome P450 Resistance and detoxification of
pesticide
Edi et al.,2014
Boisduval Tetranychus
cinnabarinus
Abamectin and
fenpropathrin
Carboxylesterases, mixed
function oxidase, glutathione
S-transferases, and
hydrolases,
Resistance Lin et al.,2009
Green peach aphid Myzus persicae Neonicotinoid
insecticides
Cytochrome P450 Resistance and improve
detoxification genes
Puinean et al.,2010
Yellow fever
mosquito
Aedes aegypti Organophosphate,
carbamate and some
pyrethroid
insecticides
αand βEsterases,
mixed-function oxidases,
glutathione-S-transferase,
acetylcholinesterase, and
insensitive
acetylcholinesterase
Resistance, support to gut
microbes, play key role in insect
biology, ecology, and behavior
Flores et al.,2006
(Continued)
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TABLE 2 (Continued)
Insect common
name
Insect scientific
name
Name of
pesticide
Name of enzyme Functions Reference
Yellow fever
mosquito
Aedes aegypti DDT and
deltamethrin
Glutathione S-transferase
and dehydrochlorinase
Resistance and detoxification of
pesticides
Lumjuan et al.,2011
Annual bluegrass
weevil
Listronotus
maculicollis
Bifenthrin Cytochrome P450
monooxygenases, glutathione
S-transferases, and
carboxylesterases
Detoxification, resistance and
development of biological
products
Ramoutar et al.,2009
Yellow fever
mosquito
Aedes aegypti Permethrin,
temephos and
atrazine
Cytochrome P450
monooxygenases
Resistance Poupardin et al.,
2008
Australian sheep
blowfly
Lucilia cuprina Organophosphate
insecticides
Carboxylesterases and
acetylcholinesterase
Resistance, detoxification of
insecticides and provide
protection from external
pathogens
Jackson et al.,2013
Green peach aphid Myzus persicae Imidacloprid,
acetamiprid and
cyhalothrin
Acetylcholinesterase,
carboxylesterase,
glutathione-S-transferase,
and mixed-function oxidase,
superoxide dismutase,
catalase, peroxidase, amylase
Food digestion, resistance
development, breakdown of
pesticide compounds and provide
protection from external
pathogens
Cai et al.,2021
Cotton bollworm Helicoverpa armigera Esfenvalerate,
indoxacarb,
emamectin benzoate
and
chlorantraniliprole
P450 enzymes Resistance and detoxification of
pesticides
Wang et al.,2018
Australian cotton
bollworm
Helicoverpa armigera Fenvalerate Cytochrome P450
monooxygenase and
carboxylesterases
Resistance and provide protection
from external pathogens
Joußen et al.,2012
Red spider mite Tetranychus urticae Abamectin Cytochrome P450 Resistance Riga et al.,2014
Asian malaria
mosquito
Anopheles stephensi Pyrethroid and
organophosphate
insecticides
Cytochrome P450s, esterase’s,
glutathione S-transferases
and acetylcholine esterase
Resistance and detoxification of
pesticides
Safi et al.,2017
Migratory locust Locusta migratoria Carbaryl, malathion,
and deltamethrin
Cytochrome P450
monooxygenases
Resistance Guo et al.,2012
Oriental fruit fly Bactrocera dorsalis Fenitrothion Acetylcholinesterase Resistance and support to
detoxification genes
Hsu et al.,2006
African malaria
mosquito
Anopheles gambiae Deltamethrin Cytochrome P450 enzymes Resistance Yahouédo et al.,2017
White-backed
planthopper
Sogatella furcifera Imidacloprid,
deltamethrin and
triazhophos
Cytochrome P450 enzymes Detoxification of pesticides and
development of resistance
Zhou et al.,2018
Bed bug Cimex lectularius Deltamethrin Cytochrome monooxygenase,
esterase’s, glutathione
S-transferase, and
carboxylesterase
Resistance Gonzalez-Morales
and Romero,2019
Cowpea aphid Aphis craccivora Thiamethoxam Glutathione S-transferase
and mixed function oxidases
Resistance Abdallah et al.,2016
Small brown
planthopper
Laodelphax
striatellus
Chlorpyriphos and
dichlorvos
Alkaline phosphatase,
carboxylesterase,
acetylcholinesterase, acid
phosphatase, glutathione
S-transferase and cytochrome
P450 monooxygenase
Resistance and detoxification of
pesticides
Wang et al.,2010
tolerance of pesticides is interlinked with these biochemical
processes which are held in the insect body and sensitivity of
pesticides which are further degraded by metabolic enzymes
such as hydrolase, esterase, laccase, acetylcholinesterase,
carboxylesterase, glutathione S-transferase, cytochrome P450
and many more (Ismail,2020;Clark et al.,2021;Yang Y.
-X. et al.,2021;Ahmad et al.,2022b;Siddiqui et al.,2022).
Insect pests’ resistance against different pesticides by insect
gut microbial enzymes was reported (Table 2). In the midgut
of the tobacco budworm (Heliothis virescens), many essential
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enzymes were purified, such as 58 proteinases, four cadherins,
13 aminopeptidases, and five alkaline phosphatases. Other
putative detoxification enzymes include 20 cytochrome P450
oxidases, 11 glutathione S-transferases, nine esterase’s, and 15
cytochrome oxidases. These enzymes contributed to insect
physiology and reduced the toxicity of pesticides (Zhu et al.,
2011).
An investigation was conducted to understand the
enzymatic molecular mechanism for biodegradation of
chlorpyriphos, glyphosate, phoxim, and esfenvalerate. In
this study, 263 bacterial colonies were isolated from the gut
of a cricket (Teleogryllus occipitalis), cultured individually,
and examined for their degradation efficiency. Based on
morphological, physiological, and 16S rRNA analysis and
found that 55 bacteria species showed a high resemblance
to 28 genera. Among these 55 bacterial species, 18 have the
potential to degrade 50%, and six were able to degrade 70%
of chlorpyriphos