Profiling the Succession of Bacterial Communities throughout the Life Stages of a Higher Termite Nasutitermes arborum (Termitidae, Nasutitermitinae) Using 16S rRNA Gene Pyrosequencing

Convergence of gut microbiota in myrmecophagous amphibians

The gut microbiome composition of terrestrial vertebrates is known to converge in response to common specialized dietary strategies, like leaf-eating (folivory) or ant- and termite-eating (myrmecophagy). To date, such convergence has been studied in mammals and birds, but has been neglected in amphibians. Here, we analysed 15 anuran species (frogs and toads) representing five Neotropical families and demonstrated the compositional convergence of the gut microbiomes of distantly related myrmecophagous species. Specifically, we found that the gut microbial communities of bufonids and microhylids, which have independently evolved myrmecophagy, were significantly more similar than expected based on their hosts' evolutionary divergence. Conversely, we found that gut microbiome composition was significantly associated with host evolutionary history in some cases. For instance, the microbiome composition of Xenohyla truncata, one of the few known amphibians that eat fruits, was not different from those of closely related tree frogs with an arthropod generalist diet. Bacterial taxa overrepresented in myrmecophagous species relative to other host families include Paludibacter, Treponema, and Rikenellaceae, suggesting diet-mediated selection and prey-to-predator transmission likely driving the observed compositional convergence. This study provides a basis for examining the roles of the gut microbiome in host tolerance and sequestration of toxic alkaloids from ants and termites.

Succession of the microbiota in the gut of reproductives of Macrotermes subhyalinus (Termitidae) at colony foundation gives insights into symbionts transmission

Termites have co-evolved with a complex gut microbiota consisting mostly of exclusive resident taxa, but key forces sustaining this exclusive partnership are still poorly understood. The potential for primary reproductives to vertically transmit their gut microbiota (mycobiome and bacteriome) to offspring was investigated using colony foundations from field-derived swarming alates of Macrotermes subhyalinus. Metabarcoding based on the fungal internal transcribed spacer (ITS) region and the bacterial 16S rRNA gene was used to characterize the reproductives mycobiome and bacteriome over the colony foundation time. The mycobiome of swarming alates differed from that of workers of Macrotermitinae and changed randomly within and between sampling time points, highlighting no close link with the gut habitat. The fungal ectosymbiont Termitomyces was lost early from the gut of reproductives, confirming the absence of vertical transmission to offspring. Unlike fungi, the bacteriome of alates mirrored that of workers of Macroterminae. Key genera and core OTUs inherited from the mother colony mostly persisted in the gut of reproductive until the emergence of workers, enabling their vertical transmission and explaining why they were found in offspring workers. These findings demonstrate that the parental transmission may greatly contribute to the maintenance of the bacteriome and its co-evolution with termite hosts at short time scales.

Changes in Bacterial Community Structure Across the Different Life Stages of Black Soldier Fly (Hermetia illucens)

The digestive capacity of organic compounds by the black soldier fly (BSF, Hermetia illucens, Diptera: Stratiomyidae, Linnaeus, 1758) is known to rely on complex larva-microbiota interactions. Although insect development is known to be a driver of changes of bacterial communities, the fluctuations along BSF life cycle in terms of composition and diversity of bacterial communities are still unknown. In this work, we used a metabarcoding approach to explore the differences in bacterial diversity along all four BSF developmental stages: eggs, larvae, pupae, and adult. We detected not only significant differences in bacterial community composition and species richness along the development of BSF, but also nine prevalent amplicon single variants (ASVs) forming the core microbiota. Out of the 2010 ASVs identified, 160 were significantly more abundant in one of the life stages. Moreover, using PICRUSt2, we inferred 27 potential metabolic pathways differentially used among the BSF life cycle. This distribution of metabolic pathways was congruent with the bacterial taxonomic distribution among life stages, demonstrating that the functional requirements of each phase of development are drivers of bacterial composition and diversity. This study provides a better understanding of the different metabolic processes occurring during BSF development and their links to changes in bacterial taxa. This information has important implications for improving bio-waste processing in such an economically important insect species.

Soil Environments Influence Gut Prokaryotic Communities in the Larvae of the Invasive Japanese Beetle Popillia japonica Newman

Invasive scarab beetles, like the Japanese beetle Popillia japonica Newman (JB), spend most of their lives as larvae feeding in the soil matrix. Despite the potential importance of the larval gut microbial community in driving the behavior, physiology, and nutritional ecology of this invasive insect, the role of soil biological and physicochemical characteristics in shaping this community are relatively unknown. Our objectives were to (1) characterize the degree to which larval gut microbial communities are environmentally acquired, (2) examine the combined effects of the gut region (i.e., midgut, hindgut) and local soil environments on gut microbial communities, and (3) search for soil physicochemical correlates that could be useful in future studies aimed at characterizing gut microbial community variation in soil-dwelling scarabs. Gut communities from neonates that were never in contact with the soil were different from gut communities of third instar larvae collected from the field, with neonate gut communities being significantly less rich and diverse. The influence of compartment (soil, midgut, or hindgut) on prokaryotic α- and β-diversity varied with location, suggesting that JB larval gut communities are at least partially shaped by the local environment even though the influence of compartment was more pronounced. Midgut microbiota contained transient communities that varied with the surrounding soil environment whereas hindgut microbiota was more conserved. Prokaryotic communities in the hindgut clustered separately from those of soil and midgut, which displayed greater interspersion in ordination space. Soil cation exchange capacity, organic matter, water holding capacity, and texture were moderately correlated (≥29%) with gut prokaryotic microbial composition, especially within the midgut. Findings suggest that microbial communities associated with the JB gut are partially a function of adaptation to local soil environments. However, conditions within each gut compartment appear to shape those communities in transit through the alimentary canal.

Gut microbial composition in different castes and developmental stages of the invasive hornet Vespa velutina nigrithorax

Social insects are successful animal invaders. Their survival and success, and in some cases also their impact on invaded ecosystem functioning, is often mediated by symbiosis with microorganisms. Here, we report a comprehensive comparative characterization of the gut microbial communities of different castes and developmental stages of the invasive hornet Vespa velutina nigrithorax. The species recently colonized Europe, becoming a high ecological and economic concern, as it threatens pollinator survival and competes with native hornet species. We used targeted meta-genomics to describe the yeasts and bacteria gut communities of individuals of different reproductive phenotypes (workers and future queens), life stages (larvae, newly emerged individuals and adults) and colony non-living samples (nest paper and larval faeces). Bacilli, Gammaproteobacteria, Actinobacteria, Alphaproteobacteria were the most abundant classes of bacteria, and Saccharomycetes, Dothideomycetes, Tremellomycetes and Eurotiomycetes were the most represented yeast classes. We found that the microbial compositions significantly differ across developmental stages and castes, with yeast and bacterial communities switching in frequency and abundance during ontogeny and according to reproductive phenotype. Moreover, the gut microbial communities poorly mirror those found in the nest, suggesting that hornets possess a specific microbial signature. Our results provide the first metagenomic resource of the microbiome of V. velutina in Europe and suggest the importance of considering life stages, reproductive phenotypes and nest influence in order to obtain a comprehensive picture of social insect microbial communities.

Commensal Bacteria Impact a Protozoan's Integration into the Murine Gut Microbiota in a Dietary Nutrient-Dependent Manner

Our current understanding of the host-microbiota interaction in the gut is dominated by studies focused primarily on prokaryotic bacterial communities. However, there is an underappreciated symbiotic eukaryotic protistic community that is an integral part of mammalian microbiota. How commensal protozoan bacteria might interact to form a stable microbial community remains poorly understood. Here, we describe a murine protistic commensal, phylogenetically assigned as Tritrichomonas musculis, whose colonization in the gut resulted in a reduction of gut bacterial abundance and diversity in wild-type C57BL/6 mice. Meanwhile, dietary nutrient and commensal bacteria also influenced the protozoan's intestinal colonization and stability. While mice fed a normal chow diet had abundant T. musculis organisms, switching to a Western-type high-fat diet led to the diminishment of the protozoan from the gut. Supplementation of inulin as a dietary fiber to the high-fat diet partially restored the protozoan's colonization. In addition, a cocktail of broad-spectrum antibiotics rendered permissive engraftment of T. musculis even under a high-fat, low-fiber diet. Furthermore, oral administration of Bifidobacterium spp. together with dietary supplementation of inulin in the high-fat diet impacted the protozoan's intestinal engraftment in a bifidobacterial species-dependent manner. Overall, our study described an example of dietary-nutrient-dependent murine commensal protozoan-bacterium cross talk as an important modulator of the host intestinal microbiome.IMPORTANCE Like commensal bacteria, commensal protozoa are an integral part of the vertebrate intestinal microbiome. How protozoa integrate into a commensal bacterium-enriched ecosystem remains poorly studied. Here, using the murine commensal Tritrichomonas musculis as a proof of concept, we studied potential factors involved in shaping the intestinal protozoal-bacterial community. Understanding the rules by which microbes form a multispecies community is crucial to prevent or correct microbial community dysfunctions in order to promote the host's health or to treat diseases.

Variations in the relative abundance of Wolbachia in the gut of Nasutitermes arborum across life stages and castes

There are multiple forms of interactions between termites and bacteria. In addition to their gut microbiota, which has been intensively studied, termites host intracellular symbionts such as Wolbachia. These distinct symbioses have been so far approached independently and mostly in adult termites. We addressed the dynamics of Wolbachia and the microbiota of the eggs and gut for various life stages and castes of the wood-feeding termite, Nasutitermes arborum, using deep-sequencing of the 16S rRNA gene. Wolbachia was dominant in eggs as expected. Unexpectedly, it persisted in the gut of nearly all stages and castes, indicating a wide somatic distribution in termites. Wolbachia-related sequences clustered into few operational taxonomic units, but these were within the same genotype, acquired maternally. Wolbachia was largely dominant in DNA extracts from the guts of larvae and pre-soldiers (59.1%-99.1% of reads) where gut-resident lineages were less represented and less diverse. The reverse was true for the adult castes. This is the first study reporting the age-dependency of the relative abundance of Wolbachia in the termite gut and its negative correlation with the diversity of the microbiota. The possible mechanisms underlying this negative interaction are discussed.

Microbial Communities of the Gut and Nest of the Humus- and Litter-Feeding Termite Procornitermes araujoi (Syntermitinae)

The evolution of the symbiotic association with microbes allowed termites to decompose ingested lignocellulose from plant-derived substrates, including herbivore dung and soil humus. Representatives of the Syntermitinae (Termitidae) range in their feeding habits from wood and litter-feeding to humus-feeding species. However, only limited information is available about their feeding ecology and associated microbial communities. Here we conducted a study of the microbial communities associated to the termite Procornitermes araujoi using Illumina sequencing of the 16S and ITS rRNA genes. This species has been previously included in different feeding guilds. However, most aspects of its feeding ecology are unknown, especially those associated to its symbiotic microbiota. Our results showed that the microbial communities of termite guts and nest substrates of P. araujoi differed significantly for bacteria and fungi. Firmicutes dominated the bacterial gut community of both workers and soldiers, whereas Actinobacteria was found in higher prevalence in the nest walls. Sordariomycetes was the most abundant fungal class in both gut and nest samples and distinguish P. araujoi from the grass/litter feeding Cornitermes cumulans. Our results also showed that diversity of gut bacteria were higher in P. araujoi and Silvestritermes euamignathus than in the grass/litter feeders (C. cumulans and Syntermes dirus), that could indicate an adaptation of the microbial community of polyphagous termites to the higher complexity of their diets.

Harnessing microfluidic streak plate technique to investigate the gut microbiome of Reticulitermes chinensis

The termite gut microbiome is a model system to investigate microbial interactions and their associations with host. For decades, extensive research with molecular tools and conventional cultivation method has been carried out to define the microbial diversity in termite gut. Yet, many bacterial groups of the termite gut microbiome have not been successfully cultivated in laboratory. In this study, we adapted the recently developed microfluidic streak plate (MSP) technique for cultivation of termite gut microbial communities at both aerobic and anaerobic conditions. We found that 99 operational taxonomic units (OTUs) were cultivable by MSP approach and 18 OTUs were documented first time for termite gut microbiota. Further analysis of the bacterial diversities derived by culture‐dependent MSP approach and culture‐independent 16S rRNA gene typing revealed that both methods have bias in recovery of gut microbiota. In total 396 strains were isolated with MSP technique, and potential new taxa at species and/or genus levels were obtained that were phylogenetically related to Burkholderia, Micrococcus, and Dysgonomonas. Results from this study indicate that MSP technique is applicable for cultivating previously unknown and new microbial groups of termite gut microbiota.

Molecular evidence that cellulolytic bacterial genus Cohnella is widespread among Neotropical Nasutitermitinae from NE Argentina

Cohnella is a highly cellulolytic bacterial genus, which can be found in a variety of habitats. The aim of this study was to assess its presence in the digestive tract of termite species collected in North-eastern Argentina: Nasutitermes aquilinus, N. corniger and Cortaritermes fulviceps. Gut homogenates were incubated with cellulosic substrate for bacterial growth. Bacterial 16S rDNA was partially amplified using new primers for Cohnella spp. and cloned. Sequences obtained showed highest similarity (97.2-99.9%) with those of Cohnella spp. previously reported from diverse environments. Phylogenetic analysis tended to group the clones according to their host species and sampling sites. These results indicate the association of Cohnella-related intestinal symbionts with three common Neotropical termites. Their potential industrial application encourages further research.

Characterization of a novel yeast species Metschnikowia persimmonesis KCTC 12991BP (KIOM G15050 type strain) isolated from a medicinal plant, Korean persimmon calyx (Diospyros kaki Thumb)

The yeast strain Metschnikowia persimmonesis Kang and Choi et al., sp. nov. [type strain KIOM_G15050 = Korean Collection for Type Cultures (KCTC) 12991BP] was isolated from the stalk of native persimmon cultivars (Diospyros kaki Thumb) obtained from different regions of South Korea and was characterized phenotypically, genetically, and physiologically. The isolate grew between 4 and 40 °C (optimum temperature: 24–28 °C), pH 3–8 (pH optimum = 6.0), and in 0–4% NaCl solution (with optimal growth in absence of NaCl). It also exhibited strong antibiotic and antimicrobial activities. Morphologically, cells were characterized by the presence of long, needle-shaped ascospores. Based on 18S ribosomal DNA gene sequence analysis, the new species was found to belong to the genus Metschnikowia as a sister clade of Metschnikowia fructicola. We therefore conclude that this yeast isolate from D. kaki is a new member of the genus Metschnikowia and propose the name M. persimmonesis sp. nov. This strain has been deposited in the KCTC for future reference. This discovery provides a basis for future research on M. persimmonesis sp. nov., including its possible contribution to the medicinal properties of the host persimmon plant.

The Value of a Comparative Approach to Understand the Complex Interplay between Microbiota and Host Immunity

The eukaryote immune system evolved and continues to evolve within a microbial world, and as such is critically shaped by-and in some cases even reliant upon-the presence of host-associated microbial species. There are clear examples of adaptations that allow the host to simultaneously tolerate and/or promote growth of symbiotic microbiota while protecting itself against pathogens, but the relationship between immunity and the microbiome reaches far beyond simple recognition and includes complex cross talk between host and microbe as well as direct microbiome-mediated protection against pathogens. Here, we present a broad but brief overview of how the microbiome is controlled by and interacts with diverse immune systems, with the goal of identifying questions that can be better addressed by taking a comparative approach across plants and animals and different types of immunity. As two key examples of such an approach, we focus on data examining the importance of early exposure on microbiome tolerance and immune system development and function, and the importance of transmission among hosts in shaping the potential coevolution between, and long-term stability of, host-microbiome associations. Then, by comparing existing evidence across short-lived plants, mouse model systems and humans, and insects, we highlight areas of microbiome research that are strong in some systems and absent in others with the hope of guiding future research that will allow for broad-scale comparisons moving forward. We argue that such an approach will not only help with identification of generalities in host-microbiome-immune interactions but also improve our understanding of the role of the microbiome in host health.

The Gut Microbiomes of Two Pachysoma MacLeay Desert Dung Beetle Species (Coleoptera: Scarabaeidae: Scarabaeinae) Feeding on Different Diets

Micro-organisms inhabiting animal guts benefit from a protected and nutrient-rich environment while assisting the host with digestion and nutrition. In this study we compare, for the first time, the bacterial and fungal gut communities of two species of the small desert dung beetle genus Pachysoma feeding on different diets: the detritivorous P. endroedyi and the dry-dung-feeding P. striatum. Whole-gut microbial communities from 5 individuals of each species were assessed using 454 pyrosequencing of the bacterial 16S rRNA gene and fungal ITS gene regions. The two bacterial communities were significantly different, with only 3.7% of operational taxonomic units shared, and displayed intra-specific variation. The number of bacterial phyla present within the guts of P. endroedyi and P. striatum individuals ranged from 6-11 and 4-7, respectively. Fungal phylotypes could only be detected within the gut of P. striatum. Although the role of host phylogeny in Pachysoma microbiome assembly remains unknown, evidence presented in this study suggests that host diet may be a deterministic factor.

Gut Bacterial Community of the Xylophagous Cockroaches Cryptocercus punctulatus and Parasphaeria boleiriana

Cryptocercus punctulatus and Parasphaeria boleiriana are two distantly related xylophagous and subsocial cockroaches. Cryptocercus is related to termites. Xylophagous cockroaches and termites are excellent model organisms for studying the symbiotic relationship between the insect and their microbiota. In this study, high-throughput 454 pyrosequencing of 16S rRNA was used to investigate the diversity of metagenomic gut communities of C. punctulatus and P. boleiriana, and thereby to identify possible shifts in symbiont allegiances during cockroaches evolution. Our results revealed that the hindgut prokaryotic communities of both xylophagous cockroaches are dominated by members of four Bacteria phyla: Bacteroidetes, Firmicutes, Proteobacteria, and Actinobacteria. Other identified phyla were Spirochaetes, Planctomycetes, candidatus Saccharibacteria (formerly TM7), and Acidobacteria, each of which represented 1–2% of the total population detected. Community similarity based on phylogenetic relatedness by unweighted UniFrac analyses indicated that the composition of the bacterial community in the two species was significantly different (P < 0.05). Phylogenetic analysis based on the characterized clusters of Bacteroidetes, Spirochaetes, and Deltaproteobacteria showed that many OTUs present in both cockroach species clustered with sequences previously described in termites and other cockroaches, but not with those from other animals or environments. These results suggest that, during their evolution, those cockroaches conserved several bacterial communities from the microbiota of a common ancestor. The ecological stability of those microbial communities may imply the important functional role for the survival of the host of providing nutrients in appropriate quantities and balance.