Genta FA, Dillon RJ, Terra WR, Ferreira C.. Potential role for gut microbiota in cell wall digestion and glucoside detoxification in Tenebrio molitor larvae. J Insect Physiol 52: 593-601

Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, C.P. 26077, São Paulo, SP 05513-970, Brazil.
Journal of Insect Physiology (Impact Factor: 2.47). 07/2006; 52(6):593-601. DOI: 10.1016/j.jinsphys.2006.02.007
Source: PubMed


Tenebrio molitor larvae were successfully reared free of cultivatable gut lumen bacteria, yeasts and fungi using two approaches; aseptic rearing from surface sterilized eggs and by feeding larvae with antibiotic-containing food. Insects were reared on a rich-nutrient complete diet or a nutrient-poor refractory diet. A comparison of digestive enzyme activities in germ free and conventional insects containing a gut microbiota did not reveal gross differences in enzymes that degrade cell walls from bacteria (lysozyme), fungi (chitinase and laminarinase) and plants (cellulase and licheninase). This suggested that microbial-derived enzymes are not an essential component of the digestive process in this insect. However, more detailed analysis of T. molitor midgut proteins using an electrophoretic separation approach showed that some digestive enzymes were absent and others were newly expressed in microbiota-free larvae. Larvae reared in antibiotic-containing refractory wheat bran diet performed poorly in comparison with controls. The addition of saligenin, the aglycone of the plant glucoside salicin, has more deleterious effects on microbiota-free larvae than on the conventionally reared larvae, suggesting a detoxifying role of midgut microbiota. Analysis of the volatile organic compounds released from the faecal pellets of the larvae shows key differences in the profiles from conventionally reared and aseptically reared larvae. Pentadecene is a semiochemical commonly found in other beetle species. Here we demonstrate the absence of pentadecene from aseptically reared larvae in contrast to its presence in conventionally reared larvae. The results are discussed in the light of the hypothesis that microbial products play subtle roles in the life of the insect, they are involved in the digestion of refractory food, detoxification of secondary plant compounds and modify the volatile profiles of the insect host.

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    • "Microorganisms play a limited role in digestion, but they may enable phytophagous insects to overcome biochemical barriers to herbivory – for example, detoxifying fl avonoid alkaloids and the phenolic aglycones of plant glycosides. Th ey may also provide complex-B vitamins for blood-feeders and essential amino acids for phloem feeders, produce pheromone components, or withstand the colonization of the gut by non-indigenous species (including pathogens) ( Dillon and Dillon, 2004; Genta et al. , 2006a ). "
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    ABSTRACT: α-Mannosidases are enzymes which remove non-reducing terminal residues from glycoconjugates. Data on both GH47 and GH38 (Golgi and lysosomal) enzymes are available. Data on insect midgut α-mannosidases acting in digestion are preliminary and do not include enzyme sequences. T. molitor midgut α-mannosidases were separated by chromatography into two activity peaks: a major (Man1) and a minor (Man2). An antibody generated against a synthetic peptide corresponding to a sequence of α-mannosidase fragment recognizes Man2 but not Man1. That fragment was later found to correspond to TmMan2 (GenBank access KP892646), showing that the cDNA coding for Man2 is actually TmMan2. TmMan2 codes for a mature α-mannosidase with 107.5 kDa. Purified Man2 originates after SDS-PAGE one band of about 72 kDa and another of 51 kDa, which sums 123 kDa, in agreement with gel filtration (123 kDa) data. These results suggest that Man2 is processed into peptides that remain noncovalently linked within the functional enzyme. The physical and kinectical properties of purified Man1 and Man2 are similar. They have a molecular mass of 123 kDa (gel filtration), pH optimum (5.6) and response to inhibitors like swainsonine (Man1 Ki, 68 nM; Man2 Ki, 63 nM) and deoxymannojirimycin (Man1 Ki, 0.12 mM; Man2 Ki, 0.15 mM). Their substrate specificities are a little different as Man2 hydrolyzes α-1,3 and α-1,6 bonds better than α-1,2, whereas the contrary is true for Man1. Thus, they pertain to Class II (GH38 α-mannosidases), that are catabolic α-mannosidases similar to lysosomal α-mannosidase. However, Man2, in contrast to true lysosomal α-mannosidase, is secreted (immunocytolocalization data) into the midgut contents. There, Man2 may participate in digestion of fungal cell walls, known to have α-mannosides in their outermost layer. The amount of family 38 α-mannosidase sequences found in the transcriptome (454 pyrosequencing) of the midgut of 9 insects pertaining to 5 orders is perhaps related to the diet of these organisms, as suggested by a large number of lysosomal α-mannosidase in the T. molitor midgut. Copyright © 2015. Published by Elsevier Ltd.
    Insect biochemistry and molecular biology 07/2015; DOI:10.1016/j.ibmb.2015.07.012 · 3.45 Impact Factor
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    • "Usually high activity of laminarinase in insects feeding on fungi is observed. Microorganisms which possess licheninase and laminarinase, occurring in the midgut, serve rather in the detoxification processes of plant toxic aglycones than in food digestion (Scrivener et al. 1997, Azevedo et al 2003, Terra and Ferreira 2005, Genta et al. 2006). The glycosidases in the midgut of D. virgifera imago hydrolyzing a-and b-glucosidic, a-and b-galactosidic bonds showed maximum activities in acidic pH. "
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    • "These compounds often accumulate in the heartwood of the plant [109]. While many insects endogenously produce impressive arrays of detoxification enzymes or have mechanisms to sequester plant toxins, many beetle species directly benefit from detoxification enzymes produced by microbes [110,111]. For example, microbial communities associated with bark beetles feeding in phloem tissue, which serves as a conduit for toxic defensive chemicals, are highly enriched for detoxification genes [112]. "
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