The bacterial community in the gut of the Cockroach Shelfordella lateralis reflects the close evolutionary relatedness of cockroaches and termites

Synthetic diets containing a single polysaccharide disrupt gut microbial community structure and microbial interaction networks in the American cockroach

Achieving and maintaining a healthy gut microbiome has numerous benefits for the host. Host diet plays a key role in shaping the gut microbial community, and understanding how diet composition influences gut microbiome structure and stability is key to developing effective interventions to treat gut microbiome dysbiosis. We use the American cockroach (Periplaneta americana) as a model system to dissect the response of gut microbes to host diet modification. Here, we designed synthetic diets from lab-grade, purified ingredients to identify how the cockroach gut community responds to different carbohydrate components (chitin, methylcellulose, microcrystalline cellulose, pectin, starch, xylan) in otherwise balanced diets. Using 16S rRNA gene sequencing, we show that synthetic diets produce replicable shifts in the cockroach gut community diversity and phylogenetic composition, with xylan-fed insects displaying the largest alterations. Comparison with cockroaches fed whole-food diets reveal that, rather than introducing new microbes, synthetic diets alter microbiome composition by inducing blooms among taxa present basally within the cockroach gut community. Synthetic diets are also associated with less-robust, more fragmentary microbial co-occurrence networks compared to cockroaches fed whole-food diets. Our results highlight the utility of lab-grade artificial diets in microbiome research and shed light on how purified polysaccharides may exert more influence over a stable gut community to generate noticeable change than whole food-derived fibers.

Termitidicoccus mucosus gen. nov. sp. nov. a novel Verrucomicrobiota species isolated from Reticulitermes chinensis gives insights of high adaptability of symbiotic bacteria to termite gut ecosystem

Verrucomicrobiota is widely distributed in various habitats including insect guts. It was found to be prevalent in almost all investigated termite guts, whereas their physiological functions are not very clear. In this study we characterized the physiological and genomic properties of Verrucomicrobiota strain TSB47T isolated from Reticulitermes chinensis. The cells of strain TSB47T were Gram-stain-negative, non-motile, and non-spore-forming coccoid with one or more warts. 16S rRNA gene analysis showed that the closest relatives of strain TSB47T were Opitutaceae strain TAV1 and Ereboglobus luteus Ho45T (98.3% and 95.4% sequence similarity, respectively). Whole genome analysis revealed that there are a large number of glycoside hydrolase genes, amino acid metabolism genes, complete Mo-Fe nitrogenase and Fe-Fe nitrogenase gene clusters, as well as cbb3-type cytochrome oxidase gene in the genome of strain TSB47T. Strain TSB47T grows well under anaerobic and microaerophilic conditions with a strong tolerance to oxygen. Physiological and genomic characters of strain TSB47T indicated its high adaptability to termite gut ecosystem. Based on phenotypic and phylogenetic evidence, we suggest strain TSB47T as the type species of a novel genus in the family Opitutaceae, for which the name Termitidicoccus mucosus sp. nov. is proposed. The type strain is TSB47T (CCTCC AB2022447T; KCTC 102044T).

Microplastic ingestion affects hydrogen production and microbiomes in the gut of the terrestrial isopod Porcellio scaber

Microplastic (MP) is an environmental burden and enters food webs via ingestion by macrofauna, including isopods (Porcellio scaber) in terrestrial ecosystems. Isopods represent ubiquitously abundant, ecologically important detritivores. However, MP-polymer specific effects on the host and its gut microbiota are unknown. We tested the hypothesis that biodegradable (polylactic acid [PLA]) and non-biodegradable (polyethylene terephthalate [PET]; polystyrene [PS]) MPs have contrasting effects on P. scaber mediated by changes of the gut microbiota. The isopod fitness after an 8-week MP-exposure was generally unaffected, although the isopods showed avoidance behaviour to PS-food. MP-polymer specific effects on gut microbes were detected, including a stimulation of microbial activity by PLA compared with MP-free controls. PLA stimulated hydrogen emission from isopod guts, while PET and PS were inhibitory. We roughly estimated 107  kg year-1 hydrogen emitted from the isopods globally and identified their guts as anoxic, significant mobile sources of reductant for soil microbes despite the absence of classical obligate anaerobes, likely due to Enterobacteriaceae-related fermentation activities that were stimulated by lactate generated during PLA-degradation. The findings suggest negative effects of PET and PS on gut fermentation, modulation of important isopod hydrogen emissions by MP pollution and the potential of MP to affect terrestrial food webs.

Diversity and taxonomic revision of methanogens and other archaea in the intestinal tract of terrestrial arthropods

Methane emission by terrestrial invertebrates is restricted to millipedes, termites, cockroaches, and scarab beetles. The arthropod-associated archaea known to date belong to the orders Methanobacteriales, Methanomassiliicoccales, Methanomicrobiales, and Methanosarcinales, and in a few cases also to non-methanogenic Nitrososphaerales and Bathyarchaeales. However, all major host groups are severely undersampled, and the taxonomy of existing lineages is not well developed. Full-length 16S rRNA gene sequences and genomes of arthropod-associated archaea are scarce, reference databases lack resolution, and the names of many taxa are either not validly published or under-classified and require revision. Here, we investigated the diversity of archaea in a wide range of methane-emitting arthropods, combining phylogenomic analysis of isolates and metagenome-assembled genomes (MAGs) with amplicon sequencing of full-length 16S rRNA genes. Our results allowed us to describe numerous new species in hitherto undescribed taxa among the orders Methanobacteriales (Methanacia, Methanarmilla, Methanobaculum, Methanobinarius, Methanocatella, Methanoflexus, Methanorudis, and Methanovirga, all gen. nova), Methanomicrobiales (Methanofilum and Methanorbis, both gen. nova), Methanosarcinales (Methanofrustulum and Methanolapillus, both gen. nova), Methanomassiliicoccales (Methanomethylophilaceae fam. nov., Methanarcanum, Methanogranum, Methanomethylophilus, Methanomicula, Methanoplasma, Methanoprimaticola, all gen. nova), and the new family Bathycorpusculaceae (Bathycorpusculum gen. nov.). Reclassification of amplicon libraries from this and previous studies using this new taxonomic framework revealed that arthropods harbor only CO2 and methyl-reducing hydrogenotrophic methanogens. Numerous genus-level lineages appear to be present exclusively in arthropods, suggesting long evolutionary trajectories with their termite, cockroach, and millipede hosts, and a radiation into various microhabitats and ecological niches provided by their digestive tracts (e.g., hindgut compartments, gut wall, or anaerobic protists). The distribution patterns among the different host groups are often complex, indicating a mixed mode of transmission and a parallel evolution of invertebrate and vertebrate-associated lineages.

Reevaluating Symbiotic Digestion in Cockroaches: Unveiling the Hindgut's Contribution to Digestion in Wood-Feeding Panesthiinae (Blaberidae)

Cockroaches of the subfamily Panesthiinae (family Blaberidae) are among the few major groups of insects feeding on decayed wood. Despite having independently evolved the ability to thrive on this recalcitrant and nitrogen-limited resource, they are among the least studied of all wood-feeding insect groups. In the pursuit of unraveling their unique digestive strategies, we explored cellulase and xylanase activity in the crop, midgut, and hindgut lumens of Panesthia angustipennis and Salganea taiwanensis. Employing Percoll density gradient centrifugation, we further fractionated luminal fluid to elucidate how the activities in the gut lumen are further partitioned. Our findings challenge conventional wisdom, underscoring the significant contribution of the hindgut, which accounts for approximately one-fifth of cellulase and xylanase activity. Particle-associated enzymes, potentially of bacterial origin, dominate hindgut digestion, akin to symbiotic strategies observed in select termites and passalid beetles. Our study sheds new light on the digestive prowess of panesthiine cockroaches, providing invaluable insights into the evolution of wood-feeding insects and their remarkable adaptability to challenging, nutrient-poor substrates.

Exploring Gut Microbiome Variations between Popillia japonica Populations of Azores

Popillia japonica (Coleoptera: Scarabaeidae), is an emerging invasive pest in Europe and America. In the Azores, this pest was first found on Terceira Island during the sixties and soon spread to other islands. The rate of infestation differs between islands, and we hypothesized that microbiome composition could play a role. Therefore, we sampled 3rd instar larvae and soil from sites with high and low infestation rates to analyze the microbiome using next-generation sequencing. We analyzed twenty-four 16S DNA libraries, which resulted in 3278 operational taxonomic units. The alpha and beta diversity of the soil microbiome was similar between sites. In contrast, the larvae from high-density sites presented a higher bacterial gut diversity than larvae from low-density sites, with biomarkers linked to plant digestion, nutrient acquisition, and detoxification. Consequently, larvae from high-density sites displayed several enriched molecular functions associated with the families Ruminococcaceae, Clostridiaceae and Rikenellaceae. These bacteria revealed a supportive function by producing several CAZyme families and other proteins. These findings suggest that the microbiome must be one drive for the increase in P. japonica populations, thus providing a checkpoint in the establishment and spread of this pest.

Exploring Gut Microbial Dynamics and Symbiotic Interaction in Blattella germanica Using Rifampicin

Blattella germanica harbours two cohabiting symbiotic systems: an obligate endosymbiont, Blattabacterium, located inside bacteriocytes and vertically transmitted, which is key in nitrogen metabolism, and abundant and complex gut microbiota acquired horizontally (mainly by coprophagy) that must play an important role in host physiology. In this work, we use rifampicin treatment to deepen the knowledge on the relationship between the host and the two systems. First, we analysed changes in microbiota composition in response to the presence and removal of the antibiotic with and without faeces in one generation. We found that, independently of faeces supply, rifampicin-sensitive bacteria are strongly affected at four days of treatment, and most taxa recover after treatment, although some did not reach control levels. Second, we tried to generate an aposymbiotic population, but individuals that reached the second generation were severely affected and no third generation was possible. Finally, we established a mixed population with quasi-aposymbiotic and control nymphs sharing an environment in a blind experiment. The analysis of the two symbiotic systems in each individual after reaching the adult stage revealed that endosymbiont's load does not affect the composition of the hindgut microbiota, suggesting that there is no interaction between the two symbiotic systems in Blattella germanica.

Disentangling hindgut metabolism in the American cockroach through single-cell genomics and metatranscriptomics

Omnivorous cockroaches host a complex hindgut microbiota comprised of insect-specific lineages related to those found in mammalian omnivores. Many of these organisms have few cultured representatives, thereby limiting our ability to infer the functional capabilities of these microbes. Here we present a unique reference set of 96 high-quality single cell-amplified genomes (SAGs) from bacterial and archaeal cockroach gut symbionts. We additionally generated cockroach hindgut metagenomic and metatranscriptomic sequence libraries and mapped them to our SAGs. By combining these datasets, we are able to perform an in-depth phylogenetic and functional analysis to evaluate the abundance and activities of the taxa in vivo. Recovered lineages include key genera within Bacteroidota, including polysaccharide-degrading taxa from the genera Bacteroides, Dysgonomonas, and Parabacteroides, as well as a group of unclassified insect-associated Bacteroidales. We also recovered a phylogenetically diverse set of Firmicutes exhibiting a wide range of metabolic capabilities, including-but not limited to-polysaccharide and polypeptide degradation. Other functional groups exhibiting high relative activity in the metatranscriptomic dataset include multiple putative sulfate reducers belonging to families in the Desulfobacterota phylum and two groups of methanogenic archaea. Together, this work provides a valuable reference set with new insights into the functional specializations of insect gut symbionts and frames future studies of cockroach hindgut metabolism.

Insect Freeze-Tolerance Downunder: The Microbial Connection

Insects that are freeze-tolerant start freezing at high sub-zero temperatures and produce small ice crystals. They do this using ice-nucleating agents that facilitate intercellular ice growth and prevent formation of large crystals where they can damage tissues. In Aotearoa/New Zealand the majority of cold adapted invertebrates studied survive freezing at any time of year, with ice formation beginning in the rich microbiome of the gut. Some freeze-tolerant insects are known to host symbiotic bacteria and/or fungi that produce ice-nucleating agents and we speculate that gut microbes of many New Zealand insects may provide ice-nucleating active compounds that moderate freezing. We consider too the possibility that evolutionary disparate freeze-tolerant insect species share gut microbes that are a source of ice-nucleating agents and so we describe potential transmission pathways of shared gut fauna. Despite more than 30 years of research into the freeze-tolerant mechanisms of Southern Hemisphere insects, the role of exogenous ice-nucleating agents has been neglected. Key traits of three New Zealand freeze-tolerant lineages are considered in light of the supercooling point (temperature of ice crystal formation) of microbial ice-nucleating particles, the initiation site of freezing, and the implications for invertebrate parasites. We outline approaches that could be used to investigate potential sources of ice-nucleating agents in freeze-tolerant insects and the tools employed to study insect microbiomes.

Diet Influences the Gut Microbial Diversity and Olfactory Preference of the German Cockroach Blattella germanica

The gut microbiota of insects has been proven to play a role in the host's nutrition and foraging. The German cockroach, Blattella germanica, is an important vector of various pathogens and causes severe allergic reactions in humans. Food bait is an effective and frequently used method of controlling this omnivorous insect. Thus, understanding the relationships among diet, gut microbiota, and olfactory preferences could be useful for optimizing this management strategy. In this study, B. germanica was exposed to different foods, i.e., high-fat diet, high-protein diet, high-starch diet, and dog food (as control). Then their gut microbial and olfactory responses were investigated. 16S rRNA gene sequencing confirmed that the gut microbiota significantly differed across the four treatments, especially in relation to bacteria associated with the metabolism and digestion of essential components. Behavioral tests and the antenna electrophysiological responses showed that insects had a greater preference for other types of diets compared with their long-term domesticated diet. Moreover, continuously providing a single-type diet could change almost all the OR genes' expression of B. germanica, especially BgORco, which was significantly repressed compared to control. These results indicate that diet can shape the gut microbiota diversity and drive the olfactory preference of B. germanica. The association between gut microbiota profiles and diets can be utilized in managing B. germanica according to their olfactory preference.

Comparative Analysis of Brucepastera parasyntrophica gen. nov., sp. nov. and Teretinema zuelzerae gen. nov., comb. nov. (Treponemataceae) Reveals the Importance of Interspecies Hydrogen Transfer in the Energy Metabolism of Spirochetes

Most members of the family Treponemataceae (Spirochaetales) are associated with vertebrate hosts. However, a diverse clade of uncultured, putatively free-living treponemes comprising several genus-level lineages is present in other anoxic environments. The only cultivated representative to date is Treponema zuelzerae, isolated from freshwater mud. Here, we describe the isolation of strain RmG11 from the intestinal tract of cockroaches. The strain represents a novel genus-level lineage of Treponemataceae and is metabolically distinct from T. zuelzerae. While T. zuelzerae grows well on various sugars, forming acetate and H₂ as major fermentation products, strain RmG11 grew poorly on glucose, maltose, and starch, forming mainly ethanol and only small amounts of acetate and H₂. In contrast to the growth of T. zuelzerae, that of strain RmG11 was strongly inhibited at high H₂ partial pressures but improved considerably when H₂ was removed from the headspace. Cocultures of strain RmG11 with the H₂-consuming Methanospirillum hungatei produced acetate and methane but no ethanol. Comparative genomic analysis revealed that strain RmG11 possesses only a single, electron-confurcating hydrogenase that forms H₂ from NADH and reduced ferredoxin, whereas T. zuelzerae also possesses a second, ferredoxin-dependent hydrogenase that allows the thermodynamically more favorable formation of H₂ from ferredoxin via the Rnf complex. In addition, we found that T. zuelzerae utilizes xylan and possesses the genomic potential to degrade other plant polysaccharides. Based on phenotypic and phylogenomic evidence, we describe strain RmG11 as Brucepastera parasyntrophica gen. nov., sp. nov. and Treponema zuelzerae as Teretinema zuelzerae gen. nov., comb. nov. IMPORTANCE Spirochetes are widely distributed in various anoxic environments and commonly form molecular hydrogen as a major fermentation product. Here, we show that two closely related members of the family Treponemataceae differ strongly in their sensitivity to high hydrogen partial pressure, and we explain the metabolic mechanisms that cause these differences by comparative genome analysis. We demonstrate a strong boost in the growth of the hydrogen-sensitive strain and a shift in its fermentation products to acetate during cocultivation with a H₂-utilizing methanogen. Our results add a hitherto unrecognized facet to the fermentative metabolism of spirochetes and also underscore the importance of interspecies hydrogen transfer in not-obligately-syntrophic interactions among fermentative and hydrogenotrophic guilds in anoxic environments.

Genetic drift and host-adaptive features likely underlie cladogenesis of insect-associated Lachnospiraceae

Phylogenetic and functional group analysis of the genomes of anaerobic bacteria isolated from Periplaneta americana digestive tracts suggest that they represent novel Lachnospiraceae genera. PAL113 and PAL227 isolate genomes encoded short-chain fatty acid biosynthetic pathways and plant fiber and chitin catabolism and other carbohydrate utilization genes common in related Lachnospiraceae species, yet the presence of operons containing flagellar assembly pathways were among several distinguishing features. In general, PAL113 and PAL227 isolates encode an array of gene products that would enable them to thrive in the insect gut environment and potentially play a role in host diet processing. We hypothesize that cladogenesis of these isolates could be due to their oxygen sensitivity, reliance upon the host for dispersal and genetic drift and not necessarily as a result of an ongoing mutualism.

Potential use of synthetic and natural aromatic mixtures in prevention from Shelfordella lateralis сockroaches

Attractive and repellent properties of many household chemicals may be used to combat synantrophic insects, such as cockroaches. In the natural environment, Shelfordella lateralis (Walker, 1868) (Blattodea, Blattidae) lives in the area spanning Central Asia to North Africa. Furthermore, in many tropical and subtropical countries, it is common in human accomodations. In the laboratory conditions, we determined reaction of cockroaches to aromatic mixtures and medicinal plants often used in households. Attractiveness coefficient was the lowest for cosmetic mixtrures Tutti-fruti and Verbena and Bamboo; other cosmetic aromatizers did not repell this insect (Lilac, Mango) or repelled it poorly (Grapefruit, Amaretto, Pine). Food additives that significantly repelled Sh. lateralis are Apricot, Barberry and Kiwi and lower effects were produced by Biscuit, whereas Vanilla flavouring had no repellent effect. Mixtures for vaping Strawberry pie, Pear, Frozen forest, Irish Cream and Blue Magic exerted strong repellent effects on cockroaches. Low repellent effect on Sh. lateralis were exerted by vaping mixtures Pancakes with Honey, Turkish Tobacco and Grapefruit. No significant effects on the number of cockroaches were exerted by vaping mixtures Vanilla, Club Ice Cream, Blueberry Smoke, Mojito, Chocolate, Apple, Mint and Walnut. Out of the fishing lures, the strongest repellent effects on Sh. lateralis were taken by Blood Worm, Onion and Honey, and weaker effects were exerted by Corn and Vanilla. Imagoes of Sh. lateralis were most significantly repelled by essential oils from jojoba, eucalyptus, daisy, tee tree, Cao Sao Vang balsam, and also fir essential oil. Neither luring nor repellent effects on imagoes of Sh. lateralis were displayed by essential oils from lemon, aloe, peppermint and mandarin. Dry medicinal plants repelled imagoes of Sh. lateralis: inflorescences of Calendula officinalis, leaves of Artemisia absinthium, flowers of Jasminum officinale, leaves of Origanum vulgare, inflorescences of Matricaria chamomilla, inflorescences of Crataegus monogyna, leaves of Mentha x piperita, inflorescences of Achillea millefolium, leaves of Hypericum perforatum, leaves of Aristolochia clematitis and inflorescences of Tanacetum vulgare. No repellent effects on Sh. lateralis were exerted by Chelidonium majus, inflorescences of Tilia cordata and inflorescences of Helichrysum arenarium. Thus, most (40 of 58, or 69.0%) of the tested aromatic substances and medicinal plants repelled synantrophic Turkestan cockroach, while a much smaller share (31.0%) neither significantly lured nor repelled them. No aromatic mixtures attracted Sh. lateralis in our experiment.

Carriage of Brachyspira hyodysenteriae on common insect vectors

The interactions of likely insect and murine vectors of the causative agent of swine dysentery, Brachyspira hyodysenteriae, were investigated. Insects were collected and analysed from 3 pig farms positive for B hyodysenteriae. Within these farms, several Musca domestica and Orphyra adult fly, Blatta sp. cockroach digestive tracts and hover fly (Eristalis sp) pupal form contents were positive in a standard PCR assay for B hyodysenteriae, whereas all other insect samples on these and case control farms were negative. In challenge exposure studies, B hyodysenteriae DNA was detected in the digestive tract of cockroaches and M domestica flies from day 1 post-inoculation with cultured B hyodysenteriae, for up to 5 days or 10 days respectively, while control non-inoculated insects remained negative. Isolates consistent with B hyodysenteriae were only cultured from frass samples of these inoculated cockroach and flies on days 1-3 post-inoculation. Isolates consistent with B hyodysenteriae were detected by analysis of agar plates exposed to live B hyodysenteriae-inoculated adult flies wandering and feeding on these plates for 20 min per day. In generational challenge inoculation studies, B hyodysenteriae was detected in the adult emergent flies, and internal components of fly pupae on days 1-7 of the pupation period, after being inoculated with B hyodysenteriae as larvae. Five-week-old conventional mice (C3H) that consumed 2 meals of B hyodysenteriae-infected flies remained negative for B hyodysenteriae throughout the next 10 days. The results indicated that pathogenic Brachyspira sp have a limited ability to internally colonise likely insect vectors and do not readily transmit infection to mice. However, the insect vectors analysed were demonstrably capable of mechanical carriage and likely on-farm involvement in consequence.

Gut Lignocellulose Activity and Microbiota in Asian Longhorned Beetle and Their Predicted Contribution to Larval Nutrition

Anoplophora glabripennis (Asian longhorned beetle) is a wood-boring pest that can inhabit a wide range of healthy deciduous host trees in native and invaded areas. The gut microbiota plays important roles in the acquisition of nutrients for the growth and development of A. glabripennis larvae. Herein, we investigated the larval gut structure and studied the lignocellulose activity and microbial communities of the larval gut following feeding on different host trees. The larval gut was divided into foregut, midgut, and hindgut, of which the midgut is the longest, forming a single loop under itself. Microbial community composition and lignocellulose activity in larval gut extracts were correlated with host tree species. A. glabripennis larvae fed on the preferred host (Populus gansuensis) had higher lignocellulose activity and microbial diversity than larvae reared on either a secondary host (Salix babylonica) or a resistant host (Populus alba var. pyramidalis). Wolbachia was the most dominant bacteria in the gut of larvae fed on S. babylonica and P. alba var. pyramidalis, while Enterococcus and Gibbsiella were the most dominant in larvae fed on P. gansuensis, followed by Wolbachia. The lignocellulose-degrading fungus Fusarium solani was dominant in the larval gut fed on different host trees. Functional predictions of microbial communities in the larval gut fed on different resistant host trees suggested that they all play a role in degrading lignocellulose, detoxification, and fixing nitrogen, which likely contribute to the ability of these larvae to thrive in a broad range of host tree species.

Bacterial Communities in the Feces of Laboratory Reared Gampsocleis gratiosa (Orthoptera: Tettigoniidae) across Different Developmental Stages and Sexes

Simple Summary

Many insects host a diverse gut microbial community, ranging from pathogenic to obligate mutualistic organisms. Little is known about the bacteria associated with katydids. Gampsocleis gratiosa (Orthoptera, Tettigoniidae) is an economically important singing pet in China. In the present study, the bacterial communities of the laboratory-reared G. gratiosa feces were characterized using Illumina sequencing of the 16S rDNA V3-V4 region.

Abstract

We used Illumina sequencing of the 16S rDNA V3-V4 region to identify the bacterial community in laboratory-reared G. gratiosa feces across different developmental stages (1st–7th instar nymph day 0, and 0-, 7-, 14-, and 21-day adult) and sexes. In total, 14,480,559 high-quality reads were clustered into 2982 species-level operational taxonomic units (OTUs), with an average of 481.197 (±137.366) OTUs per sample. These OTUs were assigned into 25 phyla, 42 classes, 60 orders, 116 families, 241 genera, and some unclassified groups. Only 21 core OTUs were shared by all samples. The most representative phylum was Proteobacteria, followed by Firmicutes, Bacteroidetes, and Acidobacteria. At the genus level, Kluyvera (387 OTUs), Obesumbacterium (339 OTUs), Buttiauxella (296 OTUs), Lactobacillus (286 OTUs), and Hafnia (152 OTUs) were dominant bacteria. The early-instar nymphs harbored a similar bacterial community with other developmental stages, which contain higher species diversity. Both principal coordinate analysis (PCoA) and non-metric multidimensional scaling analysis (NMDS) failed to provide a clear clustering based on the developmental stages and sexes. Overall, we assume that G. gratiosa transmits bacteria vertically by eating contaminated eggshells, and both developmental stages and sexes had no significant effect on the fecal bacterial community.

The Bacterial Microbiota of Edible Insects Acheta domesticus and Gryllus assimilis Revealed by High Content Analysis

In the concept of novel food, insects reared under controlled conditions are considered mini livestock. Mass-reared edible insect production is an economically and ecologically beneficial alternative to conventional meat gain. Regarding food safety, insect origin ingredients must comply with food microbial requirements. House crickets (Acheta domesticus) and Jamaican field crickets (Gryllus assimilis) are preferred insect species that are used commercially as food. In this study, we examined cricket-associated bacterial communities using amplicon-based sequencing of the 16S ribosomal RNA gene region (V3–V4). The high taxonomic richness of the bacterial populations inhabiting both tested cricket species was revealed. According to the analysis of alpha and beta diversity, house crickets and Jamaican field crickets displayed significantly different bacterial communities. Investigation of bacterial amplicon sequence variants (ASVs) diversity revealed cricket species as well as surface and entire body-associated bacterial assemblages. The efficiency of crickets processing and microbial safety were evaluated based on viable bacterial counts and identified bacterial species. Among the microorganisms inhabiting both tested cricket species, the potentially pathogenic bacteria are documented. Some bacteria representing identified genera are inhabitants of the gastrointestinal tract of animals and humans, forming a normal intestinal microflora and performing beneficial probiotic functions. The novel information on the edible insect-associated microbiota will contribute to developing strategies for cricket processing to avoid bacteria-caused risks and reap the benefits.

Enrichment of Anaerobic Microbial Communities from Midgut and Hindgut of Sun Beetle Larvae (Pachnoda marginata) on Wheat Straw: Effect of Inoculum Preparation

The Pachnoda marginata larva have complex gut microbiota capable of the effective conversion of lignocellulosic biomass. Biotechnological utilization of these microorganisms in an engineered system can be achieved by establishing enrichment cultures using a lignocellulosic substrate. We established enrichment cultures from contents of the midgut and hindgut of the beetle larva using wheat straw in an alkaline medium at mesophilic conditions. Two different inoculation preparations were used: procedure 1 (P1) was performed in a sterile bench under oxic conditions using 0.4% inoculum and small gauge needles. Procedure 2 (P2) was carried out under anoxic conditions using more inoculum (4%) and bigger gauge needles. Higher methane production was achieved with P2, while the highest acetic acid concentrations were observed with P1. In the enrichment cultures, the most abundant bacterial families were Dysgonomonadaceae, Heliobacteriaceae, Ruminococcaceae, and Marinilabiliaceae. Further, the most abundant methanogenic genera were Methanobrevibacter, Methanoculleus, and Methanosarcina. Our observations suggest that in samples processed with P1, the volatile fatty acids were not completely converted to methane. This is supported by the finding that enrichment cultures obtained with P2 included acetoclastic methanogens, which might have prevented the accumulation of acetic acid. We conclude that differences in the inoculum preparation may have a major influence on the outcome of enrichment cultures from the P. marginata larvae gut.

Of Cockroaches and Symbionts: Recent Advances in the Characterization of the Relationship between Blattella germanica and Its Dual Symbiotic System

Mutualistic stable symbioses are widespread in all groups of eukaryotes, especially in insects, where symbionts have played an essential role in their evolution. Many insects live in obligate relationship with different ecto- and endosymbiotic bacteria, which are needed to maintain their hosts’ fitness in their natural environment, to the point of even relying on them for survival. The case of cockroaches (Blattodea) is paradigmatic, as both symbiotic systems coexist in the same organism in two separated compartments: an intracellular endosymbiont (Blattabacterium) inside bacteriocytes located in the fat body, and a rich and complex microbiota in the hindgut. The German cockroach Blattella germanica is a good model for the study of symbiotic interactions, as it can be maintained in the laboratory in controlled populations, allowing the perturbations of the two symbiotic systems in order to study the communication and integration of the tripartite organization of the host–endosymbiont–microbiota, and to evaluate the role of symbiotic antimicrobial peptides (AMPs) in host control over their symbionts. The importance of cockroaches as reservoirs and transmission vectors of antibiotic resistance sequences, and their putative interest to search for AMPs to deal with the problem, is also discussed.

Microbial colonization promotes model cockroach gut tissue growth and development

BACKGROUND

Digestive tissues are essential for diet processing and nutrient accessibility, especially in omnivores, and these functions occur despite and in collaboration with dynamic microbial communities that reside within and upon these tissues. Prolonged host development and reduced digestive tissue sizes have been observed in germ-free animals, and normal host phenotypes were recovered following the re-introduction of typical gut microbiomes via coprophagy.

RESULTS

High-resolution histological analyses of Periplaneta americana cockroach digestive tissues revealed that total prevention of microbial colonization of the gut had severe impacts on the growth and development of gut tissues, especially the posterior midgut and anterior hindgut subcompartments that are expected to be colonized and inhabited by the greatest number of bacteria. Juveniles that were briefly exposed to normal gut microbiota exhibited a partial gut morphological recovery, suggesting that a single inoculation was insufficient. These data highlight gut microbiota as integral to normal growth and development of tissues they are in direct contact with and, more broadly, the organism in which they reside.

CONCLUSIONS

We draw on these data, host life history traits (i.e. multigenerational cohousing, molting, and filial coprophagy and exuvia feeding), and previous studies to suggest a host developmental model in which gut tissues reflect a conflict-collaboration dynamic where 1) nutrient-absorptive anterior midgut tissues are in competition with transient and resident bacteria for easily assimilable dietary nutrients and whose growth is least-affected by the presence of gut bacteria and 2) posterior midgut, anterior hindgut, and to a lesser degree, posterior hindgut tissues are significantly impacted by gut bacterial presence because they are occupied by the greatest number of bacteria and the host is relying upon, and thus collaborating with, them to assist with complex polysaccharide catabolism processing and nutrient provisioning (i.e. short-chain fatty acids).

Culture-Independent and Culture-Dependent Characterization of the Black Soldier Fly Gut Microbiome Reveals a Large Proportion of Culturable Bacteria with Potential for Industrial Applications

Black soldier fly larvae (BSFL) are fast-growing, resilient insects that can break down a variety of organic substrates and convert them into valuable proteins and lipids for applications in the feed industry. Decomposition is mediated by an abundant and versatile gut microbiome, which has been studied for more than a decade. However, little is known about the phylogeny, properties and functions of bacterial isolates from the BSFL gut. We therefore characterized the BSFL gut microbiome in detail, evaluating bacterial diversity by culture-dependent methods and amplicon sequencing of the 16S rRNA gene. Redundant strains were identified by genomic fingerprinting and 105 non-redundant isolates were then tested for their ability to inhibit pathogens. We cultivated representatives of 26 genera, covering 47% of the families and 33% of the genera detected by amplicon sequencing. Among these isolates, we found several representatives of the most abundant genera: Morganella, Enterococcus, Proteus and Providencia. We also isolated diverse members of the less-abundant phylum Actinobacteria, and a novel genus of the order Clostridiales. We found that 15 of the isolates inhibited at least one of the tested pathogens, suggesting a role in helping to prevent colonization by pathogens in the gut. The resulting culture collection of unique BSFL gut bacteria provides a promising resource for multiple industrial applications.

Differences in Gut Microbiome Composition Between Sympatric Wild and Allopatric Laboratory Populations of Omnivorous Cockroaches

Gut microbiome composition is determined by a complex interplay of host genetics, founder’s effects, and host environment. We are using omnivorous cockroaches as a model to disentangle the relative contribution of these factors. Cockroaches are a useful model for host–gut microbiome interactions due to their rich hindgut microbial community, omnivorous diet, and gregarious lifestyle. In this study, we used 16S rRNA sequencing to compare the gut microbial community of allopatric laboratory populations of Periplaneta americana as well as sympatric, wild-caught populations of P. americana and Periplaneta fuliginosa, before and after a 14 day period of acclimatization to a common laboratory environment. Our results showed that the gut microbiome of cockroaches differed by both species and rearing environment. The gut microbiome from the sympatric population of wild-captured cockroaches showed strong separation based on host species. Laboratory-reared and wild-captured cockroaches from the same species also exhibited distinct gut microbiome profiles. Each group of cockroaches had a unique signature of differentially abundant uncharacterized taxa still present after laboratory cultivation. Transition to the laboratory environment resulted in decreased microbiome diversity for both species of wild-caught insects. Interestingly, although laboratory cultivation resulted in similar losses of microbial diversity for both species, it did not cause the gut microbiome of those species to become substantially more similar. These results demonstrate how competing factors impact the gut microbiome and highlight the need for a greater understanding of host–microbiome interactions.

Methanogenesis in the Digestive Tracts of the Tropical Millipedes Archispirostreptus gigas (Diplopoda, Spirostreptidae) and Epibolus pulchripes (Diplopoda, Pachybolidae)

Methanogens represent the final decomposition step in anaerobic degradation of organic matter, occurring in the digestive tracts of various invertebrates. However, factors determining their community structure and activity in distinct gut sections are still debated. In this study, we focused on the tropical millipede species Archispirostreptus gigas (Diplopoda, Spirostreptidae) and Epibolus pulchripes (Diplopoda, Pachybolidae), which release considerable amounts of methane. We aimed to characterize relationships between physicochemical parameters, methane production rates, and methanogen community structure in the two major gut sections, midgut and hindgut. Microsensor measurements revealed that both sections were strictly anoxic, with reducing conditions prevailing in both millipedes. Hydrogen concentration peaked in the anterior hindgut of E. pulchripes. In both species, the intestinal pH was significantly higher in the hindgut than in the midgut. An accumulation of acetate and formate in the gut indicated bacterial fermentation activities in the digestive tracts of both species. Phylogenetic analysis of 16S rRNA genes showed a prevalence of Methanobrevibacter spp. (Methanobacteriales), accompanied by a small fraction of so-far-unclassified "Methanomethylophilaceae" (Methanomassiliicoccales), in both species, which suggests that methanogenesis is mostly hydrogenotrophic. We conclude that anoxic conditions, negative redox potential, and bacterial production of hydrogen and formate promote gut colonization by methanogens. The higher activities of methanogens in the hindgut are explained by the higher pH of this compartment and their association with ciliates, which are restricted to this compartment and present an additional source of methanogenic substrates. IMPORTANCE Methane (CH₄) is the second most important atmospheric greenhouse gas after CO₂ and is believed to account for 17% of global warming. Methanogens are a diverse group of archaea and can be found in various anoxic habitats, including digestive tracts of plant-feeding animals. Termites, cockroaches, the larvae of scarab beetles, and millipedes are the only arthropods known to host methanogens and emit large amounts of methane. Millipedes are ranked as the third most important detritivores after termites and earthworms, and they are considered keystone species in many terrestrial ecosystems. Both methane-producing and non-methane-emitting species of millipedes have been observed, but what limits their methanogenic potential is not known. In the present study, we show that physicochemical gut conditions and the distribution of symbiotic ciliates are important factors determining CH₄ emission in millipedes. We also found close similarities to other methane-emitting arthropods, which might be associated with their similar plant-feeding habits.

Characterization and phylogenomic analysis of Breznakiella homolactica gen. nov. sp. nov. indicate that termite gut treponemes evolved from non-acetogenic spirochetes in cockroaches

Spirochetes of the genus Treponema are surprisingly abundant in termite guts, where they play an important role in reductive acetogenesis. Although they occur in all termites investigated, their evolutionary origin is obscure. Here, we isolated the first representative of 'termite gut treponemes' from cockroaches, the closest relatives of termites. Phylogenomic analysis revealed that Breznakiella homolactica gen. nov. sp. nov. represents the most basal lineage of the highly diverse 'termite cluster I', a deep-branching sister group of Treponemataceae (fam. 'Termitinemataceae') that was present already in the cockroach ancestor of termites and subsequently coevolved with its host. Breznakiella homolactica is obligately anaerobic and catalyses the homolactic fermentation of both hexoses and pentoses. Resting cells produced acetate in the presence of oxygen. Genome analysis revealed the presence of pyruvate oxidase and catalase, and a cryptic potential for the formation of acetate, ethanol, formate, CO₂ and H₂ - the fermentation products of termite gut isolates. Genes encoding key enzymes of reductive acetogenesis, however, are absent, confirming the hypothesis that the ancestral metabolism of the cluster was fermentative, and that the capacity for acetogenesis from H₂ plus CO₂ - the most intriguing property among termite gut treponemes - was acquired by lateral gene transfer.

Localization of bacterial communities within gut compartments across Cephalotes turtle ants

Microbial communities within the animal digestive tract often provide important functions for their hosts. The composition of eukaryotes' gut bacteria can be shaped by host diet, vertical bacterial transmission, and physiological variation within the digestive tract. In several ant taxa, recent findings have demonstrated that nitrogen provisioning by symbiotic bacteria makes up for deficiencies in herbivorous diets. Using 16S rRNA amplicon sequencing and qPCR, this study examined bacterial communities at a fine scale across one such animal group, the turtle ant genus Cephalotes We analyzed the composition and colonization density across four portions of the digestive tract to understand how bacterial diversity is structured across gut compartments, potentially allowing for specific metabolic functions of benefit to the host. In addition, we aimed to understand if caste differentiation or host relatedness influences the gut bacterial communities of Cephalotes ants. Microbial communities were found to vary strongly across Cephalotes gut compartments in ways that transcend both caste and host phylogeny. Despite this, caste and host phylogeny still have detectable effects. We demonstrated microbial community divergence across gut compartments, possibly due to the varying function of each gut compartment for digestion.IMPORTANCE Gut compartments play an important role in structuring the microbial community within individual ants. The gut chambers of the turtle ant digestive tract differ remarkably in symbiont abundance and diversity. Furthermore, caste type explains some variation in the microbiome composition. Finally, the evolutionary history of the Cephalotes species structures the microbiome in our study, which elucidates a trend in which related ants maintain related microbiomes, conceivably owing to co-speciation. Amazingly, gut compartment-specific signatures of microbial diversity, relative abundance, composition, and abundance have been conserved over Cephalotes evolutionary history, signifying that this symbiosis has been largely stable for over 50 million years.

Hindgut microbiota reflects different digestive strategies in dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae)

Gut microbes play an important role in the biology and evolution of insects. Australian native dung beetles (Scarabaeinae) present an opportunity to study gut microbiota in an evolutionary context as they come from two distinct phylogenetic lineages and some species in each lineage have secondarily adapted to alternative or broader diets. In this study, we characterised the hindgut bacterial communities found in 21 species of dung beetles across two lineages using 16S rRNA sequencing. We found that gut microbial diversity was more dependent on host phylogeny and gut morphology than specific dietary preferences or environment. In particular, gut microbial diversity was highest in the endemic, flightless genus Cephalodesmius that feeds on a broad range of composted organic matter. The hindgut of Cephalodesmius harbours a highly conserved core set of bacteria suggesting that the bacteria are symbiotic. Symbiosis is supported by the persistence of the core microbiota across isolated beetle populations and between species in the genus. A co-evolutionary relationship is supported by the expansion of the hindgut to form a fermentation chamber and the fermentative nature of the core microbes. In contrast, Australian species of the widespread dung beetle genus Onthophagus, specialise on a single food resource such as dung or fungus, exhibit minimal food processing behaviour, have a short, narrow hindgut and a variable gut microbiota with relatively few core bacterial taxa. A conserved, complex gut microbiota is hypothesised to be unnecessary for this highly mobile genus.IMPORTANCE Dung beetles are a very important part of an ecosystem because of their role in the removal and decomposition of vertebrate dung. It has been suspected that symbiotic gut bacteria facilitate this role, a hypothesis that we have explored with high throughput barcoding. We found that differences in hindgut morphology had the greatest effect on the bacterial community composition. Species with a hindgut fermentation chamber harboured a distinctly different hindgut community compared to those species with a narrow, undifferentiated hindgut. Diet and phylogeny were also associated with differences in gut community. Further understanding of the relationships between dung beetles and their gut microbes will provide insights into the evolution of their behaviours and how gut communities contribute to their fitness.

Disentangling the Relative Roles of Vertical Transmission, Subsequent Colonizations, and Diet on Cockroach Microbiome Assembly

A multitude of factors affect the assemblies of complex microbial communities associated with animal hosts, with implications for community flexibility, resilience, and long-term stability; however, their relative effects have rarely been deduced. Here, we use a tractable lab model to quantify the relative and combined effects of parental transmission (egg case microbiome present/reduced), gut inocula (cockroach versus termite gut provisioned), and varying diets (matched or unmatched with gut inoculum source) on gut microbiota structure of hatchlings of the omnivorous cockroach Shelfordella lateralis using 16S rRNA gene (rDNA) amplicon sequencing. We show that the presence of a preexisting bacterial community via vertical transmission of microbes on egg cases reduces subsequent microbial invasion, suggesting priority effects that allow initial colonizers to take a strong hold and which stabilize the microbiome. However, subsequent inoculation sources more strongly affect ultimate community composition and their ecological networks, with distinct host-taxon-of-origin effects on which bacteria establish. While this is so, communities respond flexibly to specific diets in ways that consequently impact predicted community functions. In conclusion, our findings suggest that inoculations drive communities toward different stable states depending on colonization and extinction events, through ecological host-microbe relations and interactions with other gut bacteria, while diet in parallel shapes the functional capabilities of these microbiomes. These effects may lead to consistent microbial communities that maximize the extended phenotype that the microbiota provides the host, particularly if microbes spend most of their lives in host-associated environments.IMPORTANCE When host fitness is dependent on gut microbiota, microbial community flexibility and reproducibility enhance host fitness by allowing fine-tuned environmental tracking and sufficient stability for host traits to evolve. Our findings lend support to the importance of vertically transmitted early-life microbiota as stabilizers, through interactions with potential colonizers, which may contribute to ensuring that the microbiota aligns within host fitness-enhancing parameters. Subsequent colonizations are driven by microbial composition of the sources available, and we confirm that host-taxon-of-origin affects stable subsequent communities, while communities at the same time retain sufficient flexibility to shift in response to available diets. Microbiome structure is thus the result of the relative impact and combined effects of inocula and fluctuations driven by environment-specific microbial sources and digestive needs. These affect short-term community structure on an ecological time scale but could ultimately shape host species specificities in microbiomes across evolutionary time, if environmental conditions prevail.

Development and application of aerobic, chemically defined media for Dysgonomonas

Members of Dysgonomonas are Gram-stain-negative, non-motile, facultatively anaerobic coccobacilli originally described in relation to their isolation from stool and wounds of human patients (CDC group DF-3). More recently, Dysgonomonas have been found to be widely distributed in terrestrial environments and are particularly enriched in insect systems. Their prevalence in xylophagous insects such as termites and wood-feeding cockroaches, as well as in soil-fed microbial fuel cells, elicit interest in lignocellulose degradation and biofuel production, respectively. Their occurrence in mosquito and fruit fly have implications relating to symbiosis, host immunology and developmental biology. Additionally, their presence in termite, mosquito and nematode present novel opportunities for pest and vector control. Currently, the absolute growth requirements of Dysgonomonas are unknown, and they are commonly cultured under anaerobic conditions on complex media containing blood, peptones, tryptones, and yeast, plant or meat extracts. Restrictive and undefined culturing conditions preclude physiological and genetic studies, and thus further understanding of their metabolic potential. Here we describe the requirements for growth of termite-derived Dysgonomonas isolates and create parallel complex, defined and minimal media that permit vigorous and reliable aerobic growth. Furthermore, we show that these media can be used to easily enrich for Dysgonomonas isolates from densely-colonized and microbially-diverse environmental samples.

Bacteria associated with cockroaches: health risk or biotechnological opportunity?

Abstract

Cockroaches have existed for 300 million years and more than 4600 extant species have been described. Throughout their evolution, cockroaches have been associated with bacteria, and today Blattabacterium species flourish within specialized bacteriocytes, recycling nitrogen from host waste products. Cockroaches can disseminate potentially pathogenic bacteria via feces and other deposits, particularly members of the family Enterobacteriaceae, but also Staphylococcus and Mycobacterium species, and thus, they should be cleared from sites where hygiene is essential, such as hospitals and kitchens. On the other hand, cockroaches also carry bacteria that may produce metabolites or proteins with potential industrial applications. For example, an antibiotic-producing Streptomyces strain was isolated from the gut of the American cockroach Periplaneta americana. Other cockroach-associated bacteria, including but not limited to Bacillus, Enterococcus, and Pseudomonas species, can also produce bioactive metabolites that may be suitable for development as pharmaceuticals or plant protection products. Enzymes that degrade industrially relevant substrates, or that convert biomasses into useful chemical precursors, are also expressed in cockroach-derived bacteria and could be deployed for use in the food/feed, paper, oil, or cosmetics industries. The analysis of cockroach gut microbiomes has revealed a number of lesser-studied bacteria that may form the basis of novel taxonomic groups. Bacteria associated with cockroaches can therefore be dangerous or useful, and this review explores the bacterial clades that may provide opportunities for biotechnological exploitation.

Key points

• Members of the Enterobacteriaceae are the most frequently cultivated bacteria from cockroaches.

• Cultivation-independent studies have revealed a diverse community, led by the phyla Bacteroidetes and Firmicutes.

• Although cockroaches may carry pathogenic bacteria, most strains are innocuous and may be useful for biotechnological applications.

Role of the gut microbiome in mediating standard metabolic rate after dietary shifts in the viviparous cockroach, Diploptera punctata

Diet may be a significant determinant of insect gut microbiome composition. However, the extent to which dietary shifts shape both the composition and relevant functions of insect gut microbiomes, and ultimately impact host energy balance (i.e. metabolic phenotype), is not well understood. We investigated the impacts of diet switching on Diploptera punctata females maintained on a dog food (DF) diet relative to those fed a comparatively sub-optimal cellulose-amended dog food (CADF) diet for 4 weeks. After this period, dietary shift resulted in a significantly higher average mass-specific standard metabolic rate (SMR) in CADF-fed females compared with DF-fed females. We also uncovered significant 13C-enrichment in DF-fed insect samples relative to CADF-fed insect samples and lowered bacterial essential amino acid (EAA) provisioning in CADF-fed samples. Differences in SMR and EAA provisioning were not accompanied by significant differences in overall microbiome composition between the two groups. However, cellulolytic and nitrogen-fixing bacterial families dominant in wild omnivorous cockroaches and wood-feeding termites were significantly enriched in CADF-fed females than in DF-fed females, at the end of the study. We propose that these changes in microbiome composition after dietary shifts are associated with changes in EAA provisioning and possibly SMR. Further studies are needed to comprehensively understand the relative importance of gut microbial functions among the complexity of factors known to underscore SMR responses in insects under varying dietary conditions.

Nutritional symbiosis and ecology of host-gut microbe systems in the Blattodea

Cockroaches and termites (Order: Blattodea) have been the subject of substantial research attention for over a century due, in part, to a subset of them having a strong propensity to cohabitate with humans and their structures. Recent research has led to numerous insights into their behavior, physiology, and ecology, as well as their ability to harbor taxonomically diverse microbial communities within their digestive systems, which include taxa that contribute to host growth and development. Further, recent investigations into the physiological and behavioral adaptations that enable recalcitrant polysaccharide digestion and the maintenance of microbial symbionts in cockroaches and termites suggests that symbionts contribute significantly to nutrient provisioning and processing.

Cultivable, Host-Specific Bacteroidetes Symbionts Exhibit Diverse Polysaccharolytic Strategies

Beneficial gut microbes can facilitate insect growth on diverse diets. The omnivorous American cockroach, Periplaneta americana (Insecta: Blattodea), thrives on a diet rich in plant polysaccharides and harbors a species-rich gut microbiota responsive to host diet. Bacteroidetes are among the most abundant taxa in P. americana and other cockroaches, based on cultivation-independent gut community profiling, and these potentially polysaccharolytic bacteria may contribute to host diet processing. Eleven Bacteroidetes isolates were cultivated from P. americana digestive tracts, and phylogenomic analyses suggest that they were new Bacteroides, Dysgonomonas, Paludibacter, and Parabacteroides species distinct from those previously isolated from other insects, humans, and environmental sources. In addition, complete genomes were generated for each isolate, and polysaccharide utilization loci (PULs) and several non-PUL-associated carbohydrate-active enzyme (CAZyme)-coding genes that putatively target starch, pectin, and/or cellulose were annotated in each of the isolate genomes. Type IX secretion system (T9SS)- and CAZyme-coding genes tagged with the corresponding T9SS recognition and export C-terminal domain were observed in some isolates, suggesting that these CAZymes were deployed via non-PUL outer membrane translocons. Additionally, single-substrate growth and enzymatic assays confirmed genomic predictions that a subset of the Bacteroides and Dysgonomonas isolates could degrade starch, pectin, and/or cellulose and grow in the presence of these substrates as a single sugar source. Plant polysaccharides enrich P. americana diets, and many of these gut isolates are well equipped to exploit host dietary inputs and potentially contribute to gut community and host nutrient accessibility.IMPORTANCE Gut microbes are increasingly being recognized as critical contributors to nutrient accessibility in animals. The globally distributed omnivorous American cockroach (Periplaneta americana) harbors many bacterial phyla (e.g., Bacteroidetes) that are abundant in vertebrates. P. americana thrives on a highly diverse plant-enriched diet, making this insect a rich potential source of uncharacterized polysaccharolytic bacteria. We have cultivated, completely sequenced, and functionally characterized several novel Bacteroidetes species that are endemic to the P. americana gut, and many of these isolates can degrade simple and complex polysaccharides. Cultivation and genomic characterization of these Bacteroidetes isolates further enable deeper insight into how these taxa participate in polysaccharide metabolism and, more broadly, how they affect animal health and development.

Unraveling Assemblage, Functions and Stability of the Gut Microbiota of Blattella germanica by Antibiotic Treatment

Symbiosis between prokaryotes and eukaryotes is a widespread phenomenon that has contributed to the evolution of eukaryotes. In cockroaches, two types of symbionts coexist: an endosymbiont in the fat body (Blattabacterium), and a rich gut microbiota. The transmission mode of Blattabacterium is vertical, while the gut microbiota of a new generation is mainly formed by bacterial species present in feces. We have carried out a metagenomic analysis of Blattella germanica populations, treated and non-treated with two antibiotics (vancomycin and ampicillin) over two generations to (1) determine the core of bacterial communities and potential functions of the gut microbiota and (2) to gain insights into the mechanisms of resistance and resilience of the gut microbiota. Our results indicate that the composition and functions of the bacteria were affected by treatment, more severely in the case of vancomycin. Further results demonstrated that in an untreated second-generation population that comes from antibiotic-treated first-generation, the microbiota is not yet stabilized at nymphal stages but can fully recover in adults when feces of a control population were added to the diet. This signifies the existence of a stable core in either composition and functions in lab-reared populations. The high microbiota diversity as well as the observed functional redundancy point toward the microbiota of cockroach hindguts as a robust ecosystem that can recover from perturbations, with recovery being faster when feces are added to the diet.

Phylosymbiosis across Deeply Diverging Lineages of Omnivorous Cockroaches (Order Blattodea)

The gut microbiome is shaped by both host diet and host phylogeny. However, separating the relative influence of these two factors over long periods of evolutionary time is often difficult. We conducted a 16S rRNA gene amplicon-based survey of the gut microbiome from 237 individuals and 19 species of omnivorous cockroaches from the order Blattodea. The order Blattodea represents an ancient lineage of insects that emerged over 300 million years ago, have a diverse gut microbiota, and have a typically gregarious lifestyle. All cockroaches shared a broadly similar gut microbiota, with 66 microbial families present across all species and 13 present in every individual examined. Although our network analysis of the cockroach gut microbiome showed a large amount of connectivity, we demonstrated that gut microbiota cluster strongly by host species. We conducted follow-up tests to determine if cockroaches exhibit phylosymbiosis, or the tendency of host-associated microbial communities to parallel the phylogeny of related host species. Across the full data set, gut microbial community similarity was not found to correlate with host phylogenetic distance. However, a weak but significant phylosymbiotic signature was observed using the matching cluster metric, which allows for localized changes within a phylogenetic tree that are more likely to occur over long evolutionary distances. This finding suggests that host phylogeny plays a large role in structuring the cockroach gut microbiome over shorter evolutionary distances and a weak but significant role in shaping the gut microbiome over extended periods of evolutionary time.IMPORTANCE The gut microbiome plays a key role in host health. Therefore, it is important to understand the evolution of the gut microbiota and how it impacts, and is impacted by, host evolution. In this study, we explore the relationship between host phylogeny and gut microbiome composition in omnivorous, gregarious cockroaches within the Blattodea order, an ancient lineage that spans 300 million years of evolutionary divergence. We demonstrate a strong relationship between host species identity and gut microbiome composition and found a weaker but significant role for host phylogeny in determining microbiome similarity over extended periods of evolutionary time. This study advances our understanding of the role of host phylogeny in shaping the gut microbiome over different evolutionary distances.

Ectosymbiotic bacterial microbiota densely colonize the surface of thelastomatid nematodes in the gut of the wood-feeding cockroach Panesthia angustipennis

Cockroaches generally harbor thelastomatid nematodes (pinworms) in their gut. In this study, we discovered that the surfaces of two undescribed thelastomatid species in the hindgut of the wood-feeding cockroach Panesthia angustipennis were consistently and densely colonized by bacteria. Epifluorescence microscopy using 4',6-diamidino-2-phenylindole and transmission electron microscopy revealed that several distinct morphotypes of bacteria covered almost the entire body surface of the nematodes in single or multiple layers. Sequencing analysis of 16S rRNA amplicons of either entire nematodes or sections of nematode body surfaces indicated that the associated bacterial microbiota consisted of several dominant phylotypes belonging to either Dysgonomonadaceae (Bacteroidales termite cluster V), Rikennellaceae or Ruminococcaceae. These phylotypes formed clades with sequences previously obtained from cockroach and/or termite guts. Comparisons of the bacterial community structure of the entire cockroach hindgut microbiota vs the nematode-associated microbiota suggested that these dominant bacterial phylotypes preferentially colonized the nematode surface. The two nematode species shared most of the dominant bacterial phylotypes, but the bacterial community structures differed significantly. Colonization by five predominant phylotypes was confirmed by fluorescence in situ hybridization analysis using phylotype-specific probes. Our study provides fundamental information on this previously unknown ectosymbiosis between gut bacteria and thelastomatid pinworms.

Diet is not the primary driver of bacterial community structure in the gut of litter-feeding cockroaches

BACKGROUND

Diet is a major determinant of bacterial community structure in termite guts, but evidence of its importance in the closely related cockroaches is conflicting. Here, we investigated the ecological drivers of the bacterial gut microbiota in cockroaches that feed on lignocellulosic leaf litter.

RESULTS

The physicochemical conditions determined with microsensors in the guts of Ergaula capucina, Pycnoscelus surinamensis, and Byrsotria rothi were similar to those reported for both wood-feeding and omnivorous cockroaches. All gut compartments were anoxic at the center and showed a slightly acidic to neutral pH and variable but slightly reducing conditions. Hydrogen accumulated only in the crop of B. rothi. High-throughput amplicon sequencing of bacterial 16S rRNA genes documented that community structure in individual gut compartments correlated strongly with the respective microenvironmental conditions. A comparison of the hindgut microbiota of cockroaches and termites from different feeding groups revealed that the vast majority of the core taxa in cockroaches with a lignocellulosic diet were present also in omnivorous cockroaches but absent in wood-feeding higher termites.

CONCLUSION

Our results indicate that diet is not the primary driver of bacterial community structure in the gut of wood- and litter-feeding cockroaches. The high similarity to the gut microbiota of omnivorous cockroaches suggests that the dietary components that are actually digested do not differ fundamentally between feeding groups.

First Report of Segmented Filamentous Bacteria Associated with Rhigonema Sp. (Nematoda: Rhigonematidae) Dwelling in Hindgut of Riukiaria Sp. (Diplopoda: Xystodesmidae)

We morphologically and molecularly characterized segmented filamentous bacteria (SFB) associated with Rhigonema sp. nematodes in millipede hindguts. Seventy-three Riukiaria sp. millipedes were collected from a broad-leaf forest in Japan, and nematodes were excised from the millipede’s hindguts. The occurrence rate of SFB associated with nematodes was 24 % (10/41) for males, 47 % (14/30) for females, and 100 % (2/2) for juveniles. Genomic DNA was extracted from four SFB-rich nematode heads, and we obtained 40 bacterial clones via analysis of nearly full-length 16S rDNA gene sequences. At the phylum level, Firmicutes, Proteobacteria, and Verrucomicrobia accounted for 55 %, 40 %, and 5 % of SFB, respectively. In Firmicutes, Clostridiaceae (28 %) and Lachnospiraceae (15 %) were the dominant groups. Our sequences were divided into seven and three subclades between Firmicutes and Proteobacteria in the phylogenetic tree. In the Firmicutes clade, eight sequences were classified as Lachnospiraceae with a bootstrap value >83 %. A phylogenetic tree involving known uncultured Lachnospiraceae sequences characterized the phylogenetic position of SFB associated with nematodes. Our results suggest that the association of SFB with nematode bodies was probably incidental and that SFB are not always present in millipede hindguts. Our bacterial groups corresponded to those of arthropod hindgut, and SFB associated with nematodes were inferred to belong to Lachnospiraceae. Because the Lachnospiraceae sequences obtained in this study showed specific lineages that differed from all the known deposited sequence data, these groups may be unique to Riukiaria sp.

Biosynthetic capacity, metabolic variety and unusual biology in the CPR and DPANN radiations

Candidate phyla radiation (CPR) bacteria and DPANN (an acronym of the names of the first included phyla) archaea are massive radiations of organisms that are widely distributed across Earth's environments, yet we know little about them. Initial indications are that they are consistently distinct from essentially all other bacteria and archaea owing to their small cell and genome sizes, limited metabolic capacities and often episymbiotic associations with other bacteria and archaea. In this Analysis, we investigate their biology and variations in metabolic capacities by analysis of approximately 1,000 genomes reconstructed from several metagenomics-based studies. We find that they are not monolithic in terms of metabolism but rather harbour a diversity of capacities consistent with a range of lifestyles and degrees of dependence on other organisms. Notably, however, certain CPR and DPANN groups seem to have exceedingly minimal biosynthetic capacities, whereas others could potentially be free living. Understanding of these microorganisms is important from the perspective of evolutionary studies and because their interactions with other organisms are likely to shape natural microbiome function.

Life history and functional capacity of the microbiome are altered in beta-cypermethrin-resistant cockroaches

Cockroaches are widely perceived to evolve resistance to insecticides. Over-expression of a resistance-conferring gene can be costly and may require energy and resource reallocation for metabolic and developmental processes. To evaluate whether changes in the composition of gut microbiota in Blattella germanica affected its resistance evolution to beta-cypermethrin and to determine the role of gut microbiota in host growth and development, we studied the relationship between insecticide resistance and the diversity and genetic content of gut microbiota in cockroaches. Results suggest beta-cypermethrin-resistant cockroaches (R strain) exhibited a delayed development period and reduced adult longevity compared with susceptible cockroaches (S strain). Based on 16S rRNA gene sequencing and community metagenomics, we found that the relative abundance of Lactobacillus and Acetobacteraceae were significantly lower in the R strain compared with the S strain in the foregut and midgut of both strains. Functional annotation of Kyoto Encyclopedia of Genes and Genomes (KEGG) modules of midgut genes in the two strains revealed that 10.6% were involved in metabolism, while the relative abundance in the R strain was 7.4%. Unigenes were also translated into amino acid sequences and assigned to protein families based on hits to the Carbohydrate-Active enzymes (CAZy) database. This process identified the glycoside hydrolases, glycosyl transferases and carbohydrate-binding modules of the S strain as all being significantly higher in diversity than those in the R strain. Overall, we conclude that fitness-related costs increased in the resistant strain of cockroaches compared with the susceptible strain, and the variation in insect gut microbiota, especially those related to growth and development, was an important influencing factor.

Conspecific coprophagy stimulates normal development in a germ-free model invertebrate

Microbial assemblages residing within and on animal gastric tissues contribute to various host beneficial processes that include diet accessibility and nutrient provisioning, and we sought to examine the degree to which intergenerational and community-acquired gut bacteria impact development in a tractable germ-free (GF) invertebrate model system. Coprophagy is a common behavior in cockroaches and termites that provides access to both nutrients and the primary means by which juveniles are inoculated with beneficial gut bacteria. This hypothesis was tested in the American cockroach (Periplaneta americana) by interfering with this means of acquiring gut bacteria, which resulted in GF insects that exhibited prolonged growth rates and gut tissue dysmorphias relative to wild-type (WT) P. americana. Conventionalization of GF P. americana via consumption of frass (feces) from conspecifics and siblings reared under non-sterile conditions resulted in colonization of P. americana gut tissues by a diverse microbial community and a significant (p < 0.05) recovery of WT level growth and hindgut tissue development phenotypes. These data suggest that coprophagy is essential for normal gut tissue and organismal development by introducing beneficial gut bacteria to P. americana, and that the GF P. americana model system is a useful system for examining how gut bacteria impact host outcomes.

The hindgut microbiota of praying mantids is highly variable and includes both prey-associated and host-specific microbes

Praying mantids are predators that consume a wide variety of insects. While the gut microbiome of carnivorous mammals is distinct from that of omnivores and herbivores, the role of the gut microbiome among predatory insects is relatively understudied. Praying mantids are the closest known relatives to termites and cockroaches, which are known for their diverse gut microbiota. However, little is known about the mantid gut microbiota or their importance to host health. In this work, we report the results of a 16S rRNA gene-based study of gut microbiome composition in adults and late-instar larvae of three mantid species. We found that the praying mantis gut microbiome exhibits substantial variation in bacterial diversity and community composition. The hindgut of praying mantids were often dominated by microbes that are present in low abundance or not found in the guts of their insect prey. Future studies will explore the role of these microbes in the digestion of the dietary substrates and/or the degradation of toxins produced by their insect prey.

Biotic and abiotic factors shape the microbiota of wild-caught populations of the arbovirus vector Culicoides imicola

Biting midges of the genus Culicoides are known vectors of arboviruses affecting human and animal health. However, little is known about Culicoides imicola microbiota and its influence on this insect's biology. In this study, the impact of biotic and abiotic factors on C. imicola microbiota was characterized using shotgun-metagenomic sequencing of whole-body DNA samples. Wild-caught C. imicola adult nulliparous females were sampled in two locations from Sicily, Italy. The climatic variables of temperature and soil moisture from both localities were recorded together with potential host bloodmeal sources. Shared core microbiome among C. imicola populations included Pseudomonas, Escherichia, Halomonas, Candidatus Zinderia, Propionibacterium, and Schizosaccharomyces. Specific and unique taxa were also found in C. imicola from each location, highlighting similarities and differences in microbiome composition between the two populations. DNA and protein identification showed differences in host preferences between the two populations, with Homo sapiens and Canis lupus familiaris L. being the preferred bloodmeal source in both locations. A principal component analysis showed that the combined effect of host preferences (H. sapiens) and local soil moisture factors shape the microbiome composition of wild-caught populations of C. imicola. These results contribute to characterizing the role of the microbiome in insect adaptation and its utility in predicting geographic expansion of Culicoides species with potential implications for the control of vector-borne diseases.

Bacterial Associates of a Gregarious Riparian Beetle With Explosive Defensive Chemistry

Bombardier beetles (Carabidae: Brachininae) are well known for their unique explosive defensive chemistry. These beetles are found in riparian corridors throughout the American Southwest, where they commonly form large diurnal multispecies aggregations in moist areas under rocks, in crevices, and in leaf litter. Using high throughput 16S amplicon sequencing, we provide the first microbiome survey of a bombardier beetle, Brachinus elongatulus, collected from two sites in Arizona. Two bacterial taxa were present in all individuals sampled: Enterococcus and Dysgonomonas. Enterococcus has been implicated in the production of fecal aggregation pheromone components, which have been shown to regulate aggregation in the German cockroach; it is possible that Enterococcus plays a similar role in Brachinus. Dysgonomonas was found in all the secretory cells of the defensive system and gut samples. Additional studies are needed to determine if these microbes play a role in these beetles' unique chemical defense. Results also show that the majority of B. elongatulus individuals collected from both sites were infected with Spiroplasma. Many Spiroplasma are intracellular, vertically transmitted insect symbionts that may manipulate host reproduction (e.g., cause male-killing) or provide resistance to nematodes and/or parasitoid wasps. Defensive protection could be especially beneficial to B. elongatulus, which are frequently parasitized by horsehair worms (Nematomorpha). In sum, findings suggest several testable hypotheses on the effects bacteria may have on bombardier beetle behavior and physiology.

Overlapping Community Compositions of Gut and Fecal Microbiomes in Lab-Reared and Field-Collected German Cockroaches

German cockroaches, Blattella germanica (Blattodea: Ectobiidae), are human commensals that move freely between food and waste, disseminating bacteria, including potential pathogens, through their feces. However, the relationship between the microbial communities of the cockroach gut and feces is poorly understood. We analyzed the V4 region of the 16S rRNA gene and the V9 region of the 18S rRNA gene by next-generation sequencing (NGS) to compare the bacterial and protist diversities in guts versus feces and males versus females, as well as assess variation across cockroach populations. Cockroaches harbored a diverse array of bacteria, and 80 to 90% of the operational taxonomic units (OTUs) were shared between the feces and gut. Lab-reared and field-collected cockroaches had distinct microbiota, and whereas lab-reared cockroaches had relatively conserved communities, considerable variation was observed in the microbial community composition of cockroaches collected in different apartments. Nonetheless, cockroaches from all locations shared some core bacterial taxa. The eukaryotic community in the feces of field-collected cockroaches was found to be more diverse than that in lab-reared cockroaches. These results demonstrate that cockroaches disseminate their gut microbiome in their feces, and they underscore the important contribution of the cockroach fecal microbiome to the microbial diversity of cockroach-infested homes.IMPORTANCE The German cockroach infests diverse human-built structures, including homes and hospitals. It produces potent allergens that trigger asthma and disseminates opportunistic pathogens in its feces. A comprehensive understanding of gut and fecal microbial communities of cockroaches is essential not only to understand their contribution to the biology of the cockroach, but also for exploring their clinical relevance. In this study, we compare the diversity of bacteria and eukaryotes in the cockroach gut and feces and assess the variation in the gut microbiota across cockroach populations.

Stable isotope informed genome-resolved metagenomics reveals that Saccharibacteria utilize microbially-processed plant-derived carbon

BACKGROUND

The transformation of plant photosynthate into soil organic carbon and its recycling to CO₂ by soil microorganisms is one of the central components of the terrestrial carbon cycle. There are currently large knowledge gaps related to which soil-associated microorganisms take up plant carbon in the rhizosphere and the fate of that carbon.

RESULTS

We conducted an experiment in which common wild oats (Avena fatua) were grown in a ¹³CO₂ atmosphere and the rhizosphere and non-rhizosphere soil was sampled for genomic analyses. Density gradient centrifugation of DNA extracted from soil samples enabled distinction of microbes that did and did not incorporate the ¹³C into their DNA. A 1.45-Mbp genome of a Saccharibacteria (TM7) was identified and, despite the microbial complexity of rhizosphere soil, curated to completion. The genome lacks many biosynthetic pathways, including genes required to synthesize DNA de novo. Rather, it requires externally derived nucleotides for DNA and RNA synthesis. Given this, we conclude that rhizosphere-associated Saccharibacteria recycle DNA from bacteria that live off plant exudates and/or phage that acquired ¹³C because they preyed upon these bacteria and/or directly from the labeled plant DNA. Isotopic labeling indicates that the population was replicating during the 6-week period of plant growth. Interestingly, the genome is ~ 30% larger than other complete Saccharibacteria genomes from non-soil environments, largely due to more genes for complex carbon utilization and amino acid metabolism. Given the ability to degrade cellulose, hemicellulose, pectin, starch, and 1,3-β-glucan, we predict that this Saccharibacteria generates energy by fermentation of soil necromass and plant root exudates to acetate and lactate. The genome also encodes a linear electron transport chain featuring a terminal oxidase, suggesting that this Saccharibacteria may respire aerobically. The genome encodes a hydrolase that could breakdown salicylic acid, a plant defense signaling molecule, and genes to interconvert a variety of isoprenoids, including the plant hormone zeatin.

CONCLUSIONS

Rhizosphere Saccharibacteria likely depend on other bacteria for basic cellular building blocks. We propose that isotopically labeled CO₂ is incorporated into plant-derived carbon and then into the DNA of rhizosphere organisms capable of nucleotide synthesis, and the nucleotides are recycled into Saccharibacterial genomes.

Experimental Epidemiology of Antibiotic Resistance: Looking for an Appropriate Animal Model System

Antibiotic resistance is recognized as one of the major challenges in public health. The global spread of antibiotic resistance is the consequence of a constant flow of information across multi-hierarchical interactions, involving cellular (clones), subcellular (resistance genes located in plasmids, transposons, and integrons), and supracellular (clonal complexes, genetic exchange communities, and microbiotic ensembles) levels. In order to study such multilevel complexity, we propose to establish an experimental epidemiology model for the transmission of antibiotic resistance with the cockroach Blatella germanica. This paper reports the results of five types of preliminary experiments with B. germanica populations that allow us to conclude that this animal is an appropriate model for experimental epidemiology: (i) the composition, transmission, and acquisition of gut microbiota and endosymbionts; (ii) the effect of different diets on gut microbiota; (iii) the effect of antibiotics on host fitness; (iv) the evaluation of the presence of antibiotic resistance genes in natural- and lab-reared populations; and (v) the preparation of plasmids harboring specific antibiotic resistance genes. The basic idea is to have populations with higher and lower antibiotic exposure, simulating the hospital and the community, respectively, and with a certain migration rate of insects between populations. In parallel, we present a computational model based on P-membrane computing that will mimic the experimental system of antibiotic resistance transmission. The proposal serves as a proof of concept for the development of more-complex population dynamics of antibiotic resistance transmission that are of interest in public health, which can help us evaluate procedures and design appropriate interventions in epidemiology.

Differential Ecological Specificity of Protist and Bacterial Microbiomes across a Set of Termite Species

The gut microbiome of lower termites comprises protists and bacteria that help these insects to digest cellulose and to thrive on wood. The composition of the termite gut microbiome correlates with phylogenetic distance of the animal host and host ecology (diet) in termites collected from their natural environment. However, carryover of transient microbes from host collection sites are an experimental concern and might contribute to the ecological imprints on the termite gut microbiome. Here, we set out to test whether an ecological imprint on the termite gut microbiome remains, when focusing on the persistent microbiome. Therefore, we kept five termite species under strictly controlled dietary conditions and subsequently profiled their protist and bacterial gut microbial communities using 18S and 16S rRNA gene amplicon sequencing. The species differed in their ecology; while three of the investigated species were wood-dwellers that feed on the piece of wood they live in and never leave except for the mating flight, the other two species were foragers that regularly leave their nests to forage for food. Despite these prominent ecological differences, protist microbiome structure aligned with phylogenetic relatedness of termite host species. Conversely, bacterial communities seemed more flexible, suggesting that microbiome structure aligned more strongly with the foraging and wood-dwelling ecologies. Interestingly, protist and bacterial community alpha-diversity correlated, suggesting either putative interactions between protists and bacteria, or that both types of microbes in the termite gut follow shared structuring principles. Taken together, our results add to the notion that bacterial communities are more variable over evolutionary time than protist communities and might react more flexibly to changes in host ecology.