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AIMS Microbiology, 10(1): 220–238.
DOI: 10.3934/microbiol.2024011
Received: 23 November 2023
Revised: 21 February 2024
Accepted: 22 February 2024
Published: 13 March 2024
http://www.aimspress.com/journal/microbiology
Review
Perspective on utilization of Bacillus species as plant probiotics for
different crops in adverse conditions
Shubhra Singh1 and Douglas J. H. Shyu2,*
1 Department of Tropical Agriculture and International Cooperation, National Pingtung University of
Science and Technology, Pingtung 912301, Taiwan
2 Department of Biological Science and Technology, National Pingtung University of Science and
Technology, Pingtung 912301, Taiwan
* Correspondence: Email: dshyu@mail.npust.edu.tw; Tel: +886-8-7703202#6367; Fax: +886-8-
7703202#5183.
Abstract: Plant probiotic bacteria are a versatile group of bacteria isolated from different
environmental sources to improve plant productivity and immunity. The potential of plant probiotic-
based formulations is successfully seen as growth enhancement in economically important plants. For
instance, endophytic Bacillus species acted as plant growth-promoting bacteria, influenced crops such
as cowpea and lady’s finger, and increased phytochemicals in crops such as high antioxidant content
in tomato fruits. The present review aims to summarize the studies of Bacillus species retaining
probiotic properties and compare them with the conventional fertilizers on the market. Plant probiotics
aim to take over the world since it is the time to rejuvenate and restore the soil and achieve sustainable
development goals for the future. Comprehensive coverage of all the Bacillus species used to maintain
plant health, promote plant growth, and fight against pathogens is crucial for establishing sustainable
agriculture to face global change. Additionally, it will give the latest insight into this multifunctional
agent with a detailed biocontrol mechanism and explore the antagonistic effects of Bacillus species in
different crops.
Keywords: Bacillus species; crops; endophytes; plant growth-promoting bacteria; plant probiotics;
sustainable agriculture
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1. Introduction
Chemical fertilizers are widely used in current farming systems worldwide to meet the growing
demand for food despite their high cost and severe harmful consequences for the environment and
human health. Probiotics are living bacteria that provide the host with health benefits when given in
sufficient doses. The term was initially used concerning the interactions of microorganisms with either
animal or human hosts [1]. However, due to their wide availability and emerging technologies,
researchers are interested in learning about the interaction of these beneficial microorganisms with plant
growth and development. It is interesting to note that several studies show that probiotics could enhance
crop production and improve foods’ nutritional levels including antioxidant properties [2]. Therefore,
these bacterial species are considered to belong to plant growth-promoting rhizobacteria (PGPR). They
are responsible for improving the health of plants and have been known as plant probiotics in recent
years. Plant probiotics work through direct or indirect mechanisms at physiological levels. Plant-
associated microorganisms are reported to enhance the solubilization of fixed phosphorus to available
forms for improving plant yields. This term covers probiotic bacteria in the phylum, such as
Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria [3]. This review focuses on the growth-
promoting potential of Bacillus species involved in different crops to use these beneficial species as
probiotics under biotic and abiotic stresses.
2. Plant growth-promoting Bacillus species as plant probiotics
Gram-positive Bacillus species are common in nature and can be found in practically all
environmental niches. Additionally, these species have been utilized to produce industrial, agricultural,
and medical goods [4]. Chemical fertilizers and pesticides can be replaced with antagonistic bacterial
strains as biofertilizers. They can offer fresh perspectives on improving plant growth and productivity
in case of diseases or pest infestation. For example, a rhizospheric Bacillus strain native to Kerala,
India, shows an antifungal effect towards Pythium myriotylum in addition to the chemical compound
responsible for antifungal activity [5]. A rhizospheric B. subtilis strain isolated from Himalayan regions
was found to produce the antifungal antibiotic iturin A, a lipopeptide which inhibited growth of the
phytopathogenic fungi Fusarium oxysporum and Rhizoctonia solani [6,7]. This strain could protect
tomato plants from fungal diseases and increase fruit yield. Evidently, certain B. subtilis strains isolated
from the rhizosphere of desert plants produced volatile organic compounds such as 2,3-butanediol,
which induced systemic resistance in Arabidopsis plants [7]. This triggered immunity against the
bacterial leaf pathogen Pseudomonas syringae, reducing disease incidence. A strain of B. subtilis from
potato rhizosphere showed ability to protect potatoes from common devastating scab disease caused
by Streptomyces scabies by the production of lipopeptides surfactin and iturin A, which inhibited
germination of the pathogen’s spores [8]. Another endophytic strain of B. subtilis ME9 isolate from
cassava showed a broad-spectrum antibacterial compound that inhibited bacterial leaf streak caused
by Xanthomonas phaseoli pv. Manihotis, reducing disease severity and improving cassava yields [9].
Similarly, a plant growth-promoting B. subtilis strain obtained from semi-arid regions in Africa
demonstrated salt stress tolerance and could mitigate the effects of salinity on sorghum growth through
production of osmolytes and modulation of stress-responsive genes [10].
As mentioned, the mechanism behind the growth-promoting effects of B. subtilis is associated
with probiotic properties such as biofilm formation. The biofilm formation of B. subtilis was regulated
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by specific genes in plant polysaccharides [11]. A biofilm-forming B. subtilis strain from Brazil was
capable of solubilizing insoluble phosphorus in the soil and releasing it to promote increased growth
and productivity in corn, wheat, and other plants in phosphorus-deficient soils [12]. These biofilms
provide numerous beneficial effects that stimulate the growth and health of plants. One key mechanism
is nitrogen fixation, whereby B. subtilis converts inert atmospheric nitrogen into a usable form of
nitrogen that plants can incorporate for growth. The biofilms also solubilize insoluble phosphorus in
the soil through organic acid production, making this important macronutrient plant available. Another
growth-promoting effect is the biosynthesis of antimicrobial compounds by the biofilms that protect
plants against infection by fungal, bacterial, and viral pathogens. Beyond direct nutrient contributions
and pathogen defense, B. subtilis and B. amyloliquefaciens biofilms also induce systemic resistance in
plants, priming their innate immunity to fight off diseases more effectively [13,14]. Therefore, Bacillus-
based biofertilizers can be directly applied to the surface of the soil for the enhancement of the control of
microbial growth of disease-causing pathogens. Moreover, the effects of the induction of a pest defense
system and the increased availability of plant nutrients in rhizospheres were observed [15].
3. Biocontrol mechanism of Bacillus species in stressful conditions
Bacillus species can promote growth and development in stressed conditions through complex
mechanisms, which can be grouped into various modes of action, as mentioned in Figure 1 [15,16].
Bacillus as plant probiotics have developed an arsenal of strategies to aid plants in withstanding
stressful conditions that would otherwise inhibit growth and cause damage. As mentioned above, under
stress such as drought, certain Bacillus strains provide drought resilience by synthesizing the stress
hormone abscisic acid, which triggers adaptive water-conserving responses in plants like stomatal
closure to reduce water loss through transpiration. They also form exopolysaccharide biofilms that
help retain soil moisture and prevent desiccation [17]. For salinity tolerance, Bacillus equip plants
through production of the enzyme, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which
cleaves the ethylene precursor ACC to lower deleterious ethylene levels induced by high salts. It also
facilitates osmolyte accumulation in plant cells to maintain turgor pressure and physiological functions
when stressed by hyperosmotic conditions [18,19]. In chilling temperatures, Bacillus sp. JC03 secrete
volatile organic compounds such as auxin and strigolactone that systemically induce biomass
accumulation in Arabidopsis, promoting plant growth. They also modulate the formation of protective
ice nucleating proteins to prevent intracellular freezing and frost injury [20]. Finally, in high heat
conditions, Bacillus strains HT1 to HT4 isolated from Saudi Arabia elicit the plant's own antioxidant
systems to scavenge dangerous reactive oxygen species produced as a result of heat stress. They also
synthesize beneficial heat shock proteins that confer protein stability and prevent misfolding when
plants experience spikes in temperature [21]. Through these diverse mechanisms related to plant
hormones, osmolytes, protective proteins and other compounds, Bacillus species provide plants the
biological means to withstand adverse environmental conditions and continue thriving.
Therefore, as shown in the subsequent figure, biocontrol mechanisms of Bacillus species include
a myriad of functions:
a) Biological nitrogen fixation
b) Stress-mediated enzymes, such as 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and
extracellular enzymes for hydrolyzing the cell wall
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c) Plant growth regulators, such as abscisic acid (ABA), cytokinins (CKs), gibberellic acid (GA),
and indole-3-acetic acid (IAA)
d) Siderophore production for the chelation of available iron in the rhizosphere
e) Micronutrient and macronutrient biosolubilization and biomineralization, especially
converting insoluble phosphate precipitates to soluble forms
f) Biocontrol of plant pathogens by other mechanisms, such as antibiotics production, induced
systemic resistance (ISR), quorum quenching, and microbial competition for metabolic niches
within the rhizosphere
g) Agricultural soil structure improvement and contaminated soil bioremediation, such as toxic
heavy metal species sequestration and xenobiotic compounds degradation
h) Abiotic stresses resistance enhancement [22]
Figure 1. Effect of Bacillus on plant protection in biotic and abiotic stress. Illustration
depicting the multifaceted impact of Bacillus-based probiotic mixture on rhizosphere can
help plant to restore nitrogen (N), phosphorus (P) and potassium (K) and overcome biotic
and abiotic stresses by the production of antimicrobial compounds, lytic enzymes, quorum
sensing molecules or imparting induced systemic resistance (Created with Biorender.com).
Nitrogen synthesis is essential for plant growth and development since forming amino acids
and proteins is considered an important biochemical pathway for synthesizing the macronutrients
for plants [23]. Specific organic molecules produced by some microorganisms, such as phytohormones,
are involved in plant photomorphogenesis. However, some beneficial bacteria or probiotic species are
involved in plant growth enhancement and disease resistance [24,25]. For example, auxins are
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responsible for regulating bacterial communication and coordinating other functions of plants directly
or indirectly, and some act as signaling molecules for bacterial communication. An auxin-producing
Bacillus species WM13-24 and a B. amyloliquefaciens GB03 which were isolated from the rhizosphere
of H. ammodendron were developed as biofertilizers. They were found to enhance the growth, fruit
yield, and quality of Capsicum annuum with improvement in nitrogen content, enzyme activities, and
biodiversity of viable bacteria for long-term effects [26].
Similarly, Bacillus megaterium with Azotobacter chroococcum are found to promote cucumber
growth by producing cytokinins. Cytokinins are responsible for cytokinesis, vascular cambium
sensitivity, root apical dominance, and vascular differentiation [27,28]. Under stressed conditions,
plants often produce ethylene that can inhibit specific processes that cause premature senescence, such
as root elongation or nitrogen fixation in legumes. Some bacteria produce ACC amidase to hydrolyze
ACC, the precursor molecule involved in the biosynthesis of ethylene. Therefore, these probiotic
species lower ethylene levels and protect the plant from damage [2]. Plant growth and germination of
seeds are affected by nutrient availability. Generally, root transporters are responsible for the
absorption of soluble phosphorus and nitrogen forms from the soil. However, the rhizosphere is the
bioavailable center for P and N [29]. Some effects of the beneficial Bacillus species and their bioactive
components are shown in Table 1. Bacillus species can convert the complex forms or the precipitate
forms of essential macronutrients to the available soluble forms for the plants during uptake by plant
roots. Some of the reported strains of Bacillus pumilus and B. subtilis can positively fix available
nitrogen, solubilize the phosphate, and produce auxins during in vitro studies [30,31]. It is reported
that Bacillus species have nifH gene and produce nitrogenase involved in nitrogen fixation to delay
senescence and enhance plant growth and yield [30]. In the pursuit of sustainable agriculture, researchers
are exploring innovative strategies to improve soil fertility and one promising eco-friendly approach
involves the combination of biochar and beneficial microorganisms, such as B. subtilis SL-44. This
synergistic approach not only addresses soil health but also contributes to increased agricultural
productivity [57]. SL-44, also known for its antagonistic properties against fungi, presents an
opportunity for the isolation, purification, and identification of antifungal proteins. Studies have
elucidated the antifungal protein produced by B. subtilis SL-44 has potential application in addressing
anti-fungal resistance in apple cultivation [58]. Subsequently, studies have found that the enhancement
of chromium contamination can be remediated by SL-44 strain through the addition of humic acid (HA).
The study also has suggested dual function of HA on SL-44 species in Cr (VI) reduction, augmentation
of Cr (VI) complexation, adsorption, and electronic exchange reduction in the contaminated soil [59].
Table 1. Plant growth-promoting characteristics with Bacillus species.
1
Types of species
Growth promoting characteristics
Bioactive metabolites/other contents
Inferences
Reference
Bacillus sp. LKE15
Increased shoot length, root length, and
plant fresh weight of the oriental melon
Increased synthesis of chlorophyll and
individual amino acids along with
magnesium, potassium, and phosphorus
content
Cell-free Bacillus sp. LKE15 on crop
plants has excellent potential as an organic
method of improving plant growth
[32]
Bacillus sp. WG4
Plant growth-promoting properties and
antifungal effects against Pythium
myriotylum
Pyrrolo [1,2-α] pyrazine-1,4-dione,
hexahydro-3-(phenylmethyl)
Promising application as an antifungal
plant probiotic agent alone or in
combination with other agents like
Trichoderma
[5]
Bacillus subtilis BA-142,
Bacillus megaterium-GC
subgroup A. MFD-2
Foliar application increased fruit length
and mineral contents of tomato and
cucumber fruit
none
Great potential to increase the yield,
growth, and mineral contents of tomato
and cucumber vegetable species
[33]
Bacillus subtilis LDR2
Promoting plant growth through
improved colonization of beneficial
microbes under drought stress in
Trigonella plants
High levels of ACC deaminase and
reduced ethylene concentrations
Beneficial for legumes cultivated in arid
conditions
[34]
Bacillus insolitus (strain
MAS17), and Bacillus sp.
(strains MAS617, MAS620
and MAS820)
Increased the dry matter yield of roots
(149–527% increase) and shoots (85–
281% increase), and the mass of RS
(176–790% increase) in pot experiments
Exopolysaccharides (EPS) productions
EPS-producing bacteria could serve as a
valuable tool for alleviating salinity stress
in salt-sensitive plants
[35]
Bacillus megaterium
mj1212
Increasing shoot length, root length, and
fresh weight in mustard plants
Increased chlorophyll, sucrose, glucose,
fructose, and amino acids content
Phosphate biofertilizer to improve the
plant growth
[36]
Bacillus methylotrophicus
KE2
Enhance shoot length, shoot fresh weight,
and leaf width of lettuce
Increased gibberellins and indole acetic
acid contents along with high nutritional
content
A potential candidate for increasing
nutritional contents
[37]
Continued on next page
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Types of species
Growth promoting characteristics
Bioactive metabolites/other contents
Inferences
Reference
Bacillus mojavensis
Increase the dry weight of root and shoot,
chlorophyll content, and nutrient uptake
in salt-stressed wheat plants
Bacteria containing ACC deaminase
Bacillus mojavensis could be an effective
strain to promote the growth of wheat in
saline soils
[38]
Bacillus subtilis (HYT-12-1)
37%-IAA production;
37%-phosphate solubilization;
24%-siderophores production;
85%-potential nitrogen fixation;
6%-ACC deaminase activity in tomato
seeds
High ACC deaminase activity in
gnotobiotic and greenhouse conditions
B. subtilis strain HYT-12-1 would have
great potential for industrial application as
a biofertilizer in the future
[39]
Bacillus sp. CaB5
Enhancement effect on seed germination
as well as plant growth in cowpea (Vigna
unguiculata) and lady’s finger
(Abelmoschus esculentus)
None
Potential of CaB5-based formulation for
field application to enhance the growth of
economically important plants
[40]
Bacillus vietnamensis
Plant growth and bud development with
antifungal, anti-inflammatory, anticancer,
and antibacterial activities in ginger
rhizome against Pythium myriotylum
2,4-bis (1,1-dimethylethyl) phenol
Biocontrol agent for Pythium rot in ginger
as an alternative to fungicides
[41]
Bacillus subtilis CBR05
Increased total phenol and flavonoid
contents of tomato fruits along with in
tomato fruits
Stimulated antioxidant activities and
levels of carotenoid (β-carotene and
lycopene) content
Biofertilizers-based on PGPR may be a
viable alternative to improve the
nutraceutical quality of greenhouse-
produced tomato fruits
[42]
Bacillus cereus QJ-1 bio-
organic fertilizer (BOF)
Reduces tobacco bacterial wilt disease
and improves soil quality
High nitrogen, phosphorus, and organic
matter in rhizosphere soils
BOF can improve the ecological stability
of soils and mitigate tobacco bacterial wilt
disease
[43]
Continued on next page
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Types of species
Growth promoting characteristics
Bioactive metabolites/other contents
Inferences
Reference
Bacillus biofortified
organic fertilizer (BOF)
Disease incidence was lowest (10.7%) in
BOF treatment when compared to OF
(organic fertilizer) treatment (13.1%),
along with an increase in the shoot and
root length in tomato plants
None
Management of bacterial wilt disease
under poly house conditions of Andaman
Islands
[44]
Bacillus cabrialesii BH5
Control the fungal pathogen Botrytis
cinerea in tomato rhizosphere
Cyclic lipopeptide of the fengycin family
BH5 and fengycin H are up-and-coming
candidates for biological control of B.
cinerea and the associated gray mold
[45]
Bacillus pumilus 104
Inhibited the growth of Phytophthora
nicotianae and P. palmivora in citrus
trees
Antifungal properties with antimicrobial
compounds
None
[46]
Bacillus
amyloliquefaciens Ba168
Inhibited growth of blue mold caused by
Penicillium expansum in apples
Flagellin an antifungal compound
Flagellin is one of the essential
antimicrobial substances from Ba168
[47]
Bacillus
amyloliquefaciens Ba01
Inhibited the growth and sporulation of
Streptomyces scabies in potatoes
Surfactin, iturin A, and fengycin
Bacillus species control potato common
scab in nature
[48]
Bacillus
amyloliquefaciens FZB42
Antibacterial activity against
Xanthomonas oryzae rice pathogens
Difficidin and bacilysin
Environmentally friendly and versatile in
their mode of action
[49]
Bacillus
amyloliquefaciens Ar10
Antagonistic activity against bacterial
soft rot of potato caused by
Pectobacterium carotovorum II16
Glycolipid-like compounds
Best alternatives for compounds against
the soft rot disease of potato
[50]
Bacillus subtilis V26
Effective against root canker and black
scurf Tuber (Rhizoctonia solani) on
potato
Chitosanase and proteases
Great potential to be commercialized as a
biocontrol agent
[51]
2
Other mechanisms, such as cell wall modification, metabolic response changes, and gene
expression alteration, occur during stressful conditions. Therefore, researchers focus on signaling
molecules and expression analysis to downstream the bioactive metabolites and genes in plant-microbe
interaction [52]. Quorum sensing involves cell-to-cell signaling mechanisms to regulate the pathogen
population and virulence gene expression. It is considered a crucial process that enables host
colonization and microbe survival under stressful situations [53]. Some microorganisms, such as B.
cereus and B. thuringiensis, secrete volatile metabolites. These metabolites, such as alkyl sulfides,
indoles, and terpenes, were involved in the quorum quenching mechanism, disrupt the signaling of the
pathogens in the soil microbiome, and protect the plant from diseases such as soft rot in potatoes,
carrots, etc. [54,55]. Some microorganisms, such as Bacillus and Serratia synthesize pigments that
have the ability to filter radiation to prevent the damage of nucleic acids under high light intensity [27].
Bacillus sp. uses a proton transfer system in the cytoplasm to maintain osmotic balance during pH
fluctuation conditions. The regulation of cellular metabolite activities can control protein function,
increase cellular vitality, and inhibit pathogen growth. Mechanisms such as solubilization, chelation,
modifications, and oxidation-reduction reactions were commonly utilized [56].
4. Role of antimicrobial bioactive compounds in biotic and abiotic conditions
Bacillus species can induce systemic resistance in plants and increase the uptake and translocation of
pesticides in the plant cells of the root system to control pest infestations [60]. The bacterial infection starts
with the release of crystal proteins to damage the larval midgut epithelium of the insects at the primary site,
interacting with chitin and damaging the peritrophic membranes. For instance, B. thuringiensis Cry1
protein domain III damages the peritrophic membrane of Asian corn borer [61]. In addition, B.
thuringiensis synthesized lipopeptides and polyketides in the later stages of infection. The compounds,
such as bacillaene, bacillomycin, difficidin, fegycins, iturin, macrolactin, and surfactin, could modify the
process of vacuolization, induce the formation of vesicles, cause the lysis of cell membranes, damage the
microvilli, and subsequently lead to the death of larvae [51,62]. In the cellular phospholipid bilayer, protein
surfactin is attached to calcium receptors and changes the peptide composition, while iturin forms ion-
conducting pores and increases cell membrane permeability [63]. Bacillus species suppress the pathogenic
microbial populations that infect and cause diseases of plants, such as Pseudomonas savastanoi, Ralstonia
solanacearum, and Xanthomonas axonopodis [64,65]. Bacillus species form biofilm around the root
surface and secret polyketides to destroy the membranes of pathogens and reduce diseases by changing the
morphology of cell walls and then killing the pathogens [11,35].
5. Comparative study of Bacillus-based fertilizers with conventional fertilizers and pesticides
The viability of microbial consortia of the biofertilizer depends on the inoculation method applied.
It influences the establishment of microbial populations in the rhizosphere along with the structure and
function of microbial populations. Microcapsules have been studied as the best alternative to protection
and controlled release [66]. The commonly used carrier materials include inorganic materials, such as
charcoal, clay, compost, rock phosphate pellets, talc, vermiculite, and zeolite, and organic materials,
such as diatomaceous earth, sawdust, rice bran, and wheat bran [16]. Proper formulation is key to a
successful and effective biofertilizer. A comparative chart (Table 2) highlights the advantages of
Bacillus-based biofertilizers over conventional chemical fertilizers:
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Table 2. Comparison chart highlighting the specific advantages of Bacillus-based fertilizers.
Parameters
Bacillus-Based Biofertilizers
Conventional Chemical Fertilizers
Nutrient Delivery
Provide nutrients through biological nitrogen
fixation, P solubilization, phytohormone production
Provide inorganic forms of NPK only
Soil Health
Improve soil structure, organic matter; no
accumulation of salts or chemicals
Can degrade soil quality over time,
salinization
Environmental Impact
Eco-friendly, no toxic chemical residues
Leaching causes water pollution,
eutrophication
Effectiveness
Nutrients available over longer-term; activate soil
microbiome
Nutrients easily leach away, may
require frequent re-application
Plant Growth
Promote extensive root development, stress
tolerance
Primarily provides macronutrients
only for growth
Cost
Lower cost per acre over long term
Petroleum derived, energy intensive
high cost over time
Safety
No health risks; biopesticides improve food safety
Risk of toxic metal accumulation;
pesticide residues
Yield
Increased yields due to well-developed healthy
plants
Lower yields over time as soil quality
declines
Regulatory Approval
Considered safe; no restrictive regulations
Subject to government health and
safety regulations
Natural carriers such as bacterial species must possess the capability of long-term viability;
however, the nutrient competition makes it more challenging to adapt to certain micro-habitats. This
natural selection among pathogens challenges the probiotic bio-based fertilizers [67]. In addition to
the carrier materials, the inoculum density and the response of the plant towards the inoculators are
highly influenced by root colonization that varies from bacterial division rate and distribution in the
rhizospheres [66]. Another significant issue is acclimatization to the new environment, which leads to
a decrease in the microorganism population. Accompanied by biotic and abiotic factors, it affects the
structural and functional diversity of microorganism communities. In this manner, a study of the
evaluation of probiotic inoculants towards site-specific plant associations could determine the fate and
activity in the soil [68].
Organic farming is an integrated farming system where bacterial agents are considered eco-
friendly and sustainable for increasing soil fertility and protecting plants against diseases [69]. Plant
probiotic Bacillus species can promote organic farming and reduce farmers' dependence on chemical
fertilizers and promote sustainable farming in modern agriculture. For instance, an alternative crop
production technique was applied by the inoculation of both B. subtilis FZB24 and GB03 in corn (Zea
mays L.) seedlings. They reduced the use of neonicotinoid insecticide thiamethoxam. Similar studies
have been observed with the evaluation of using thiamethoxam in tomato crops [70]. The excretion of
xylem fluid at leaf margins is called guttation, a natural phenomenon. Since the use of neonicotinoid
systemic insecticides on seeds reduces the population of bees drastically and causes significant losses
in the plant pollination phenomenon, the use of this particular chemical was banned by the European
Union [71]. On the contrary, a well-known bio-insecticide, Bacillus thuringiensis, which works
harmoniously with plants, is responsible for controlling a broad range of diverse insects for pest
management in agricultural fields [72]. Some other examples are B. cereus, B. subtilis, and B.
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amyloliquefaciens, which are also involved in pest control and management [73].
6. Perspectives and future of Bacillus-based products
There is a shred of clear evidence from previous studies that applying probiotics has long-term
effects on crop productivity in terms of improving quality and quantity. However, due to their complex
nature and lesser popularity, a solid application strategy is needed to promote the usage of probiotic
bacteria consortiums in agriculture, especially in developing countries. Studies on the mode of action
show antagonistic behavior towards pathogens, but the efficacy is decreased during cascades of
physiological events (Figure 2). With the development of novel probiotic-based fertilizers, specific
modes of action might be considered. In that case, robust screening of novel Bacillus species as
probiotic strains with potential antimicrobial metabolites can be used. This screening method may
work well with the superior kind of strains and the overall effects of the pathogen and disease. In terms
of future research, a few aspects should be given immediate consideration:
a) Recommendation of precision probiotic bacteria fertilizer: The precision fertilizer, which is
selected based on soil mineralogy and dynamics, is of utmost importance to improve crop yield
and cost-effectiveness. Initially, in vitro experimental setup should be brought up in the fields
by selecting certain districts or counties in a country. A certain number of soil types must then
be chosen as samples for mineralogy and dynamics and observed to compare conventional
kinds of fertilizers.
b) Crop quality consideration: Soil quality plays a vital role in the improvement of the quality of
most crops. However, for precise and more accurate crop-responsive probiotic application, a
suitable formulation might be used to investigate the dynamicity in the system, minimizing the
use of chemical fertilizers and promoting organic agriculture for a sustainable environment.
Moreover, public sector research institutions, fertilizer companies, and agriculture-based
industries should work together to develop a research and awareness strategy for the promotion
of probiotics bacteria in agriculture.
c) Multi-omics approach: better screening assays such as multi-omics inclusive of genomics,
proteomics, and transcriptomics are required to find the next-generation probiotic strains
among all the Bacillus species.
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Figure 2. Limitations with probiotic efficiency and stability. Schematic representation of
the challenges and limitations associated with the probiotic efficiency and stability of plant
probiotics. Relevant factors include soil characteristics, mode of action, short economic
life span, microbial competition, and acclimatization.
Every year, commercial treatments concerning novel bacterial inoculants for different crops are
growing. Government clearance for novel inoculants and formulations is not always universal and
well-established; therefore, the commercialization process requires more attention. Additionally, the
commercialization and registration of new products depend on the country [74], and rules and
regulations vary according to the country. Until now, no international agreement on biofertilizer
utilization and quality control in agricultural and horticultural industries has been established.
According to most of the protocols established by North America, a novel formulation, including
Bacillus species either using organic or inorganic carriers, must be safe and non-toxic for the environment
and human health. Current commercial Bacillus sp. products are listed in Table 3 [75–77]. However, a
few species, such as B. cereus, are considered pathogenic to humans and require clearance and
registration for large-scale production [78,79].
In conclusion, this perspective not only provides a synthesis of current knowledge on the
utilization of Bacillus species in challenging agricultural environments but also serves as a catalyst for
future research endeavors. The continued exploration of the intricate interactions between Bacillus
species and plants holds promise for advancing our understanding of plant probiotics and their pivotal
role in shaping the future of agriculture under adverse conditions.
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Table 3. Commercial biofertilizers brands in the market with bacterial strains.
Inoculators
Product
Plants
Viability
Company
B. amyloliquefaciens,
Bradyrhizobium japonicum
Nodulator® N/T Peat
Increase the yield of
soybean
24 hours on-seed
survivability
BASF
Canada Inc.
Bacillus amyloliquefaciens,
Bradyrhizobium japonicum
Nodulator® PRO 100
Soybean fungicides
24 hours on-seed
survivability
BASF
Canada Inc.
Bacillus subtilis, Bacillus
amyloliquefaciens
PrimAgro® C-Tech
Pest control in all
types of crops
6 months
Canadian
Corporation
Bacillus subtilis, Bacillus
amyloliquefaciens
BioSoil Enhancers, Inc
Pest control in all
types of crops
6 months
Arizona
Corporation
Bacillus amyloliquefaciens,
Bacillus licheniformis, Bacillus
megaterium, Bacillus pumilus,
Bacillus subtilis, Trichoderma
BioSafe® Systems
Pest control in all
types of crops
6–8 months
Arizona
Corporation
Bacillus subtilis
BioWorks®
Pest control in all
types of crops
-
Arizona
Corporation
Bacillus amyloliquefaciens, Bacillus
licheniformis, Bacillus subtilis
Blacksmith Bioscience®
Pest control in all
types of crops
6 months
Arizona
Corporation
Bacillus subtilis
Concentric Ag®
Pest control in all
types of crops
6 months
Arizona
Corporation
Bacillus amyloliquefaciens, Bacillus
subtilis, Pseudomonas monteilii
Earth Alive®
Pest control in all
types of crops
-
Arizona
Corporation
Bacillus subtilis, Bacillus
amyloliquefaciens
Impello Biosciences®
Pest control in all
types of crops
-
Arizona
Corporation
Bacillus subtilis
John and Bob's®
Pest control in all
types of crops
-
Arizona
Corporation
Bacillus subtilis, Bacillus
amyloliquefaciens
Key to Life®
Pest control in all
types of crops
-
Arizona
Corporation
Bacillus subtilis
SCD Probiotics®
Pest control in all
types of crops
-
Arizona
Corporation
Use of AI tools declaration
The authors declare they have not used artificial intelligence (AI) tools in the creation of this article.
Acknowledgments
We would like to thank Mr. Liyu Chiang for his assistance.
Conflict of interest
The authors declare no conflict of interest.
233
AIMS Microbiology Volume 10, Issue 1, 220–238.
Author Contributions
S.S.: Conceptualization, Investigation, Data Curation, Validation, Writing – Original Draft Preparation.
D.J.H.S: Conceptualization, Supervision, Project Administration, Suggestion, and Writing – Review
and Editing.
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