The influence of diet and environment on the gut microbial community of field crickets

Microbial biomarkers as indicators of sperm viability in an insect

Our understanding of microbial variation in male reproductive tissues is poorly understood, both regarding how it varies spatially across different tissues and its ability to affect male sperm and semen quality. To redress this gap, we explored the relationship between male sperm viability and male gut and reproductive tract microbiomes in the Pacific field cricket, Teleogryllus oceanicus. We selected cohorts of males within our populations with the highest and lowest natural sperm viability and characterized the bacterial microbiota present in the gut, testes, seminal vesicle, accessory glands and the spermatophore (ejaculate) using 16S ribosomal RNA gene metabarcoding. We identified bacterial taxa corresponding to sperm viability, highlighting for the first time an association between the host's microbial communities and male competitive fertilization success. We also found significant spatial variation in bacterial community structure of reproductive tissue types. Our data demonstrate the importance of considering the microbial diversity of both the host gut and reproductive tract when investigating male fertility in wildlife and potentially human clinical settings.

Screening and Identification of Protease-Producing Microorganisms in the Gut of Gryllotalpa orientalis (Orthoptera: Gryllotalpidae)

The insect gut harbors a diverse array of functional microorganisms that warrant further exploration and utilization. However, there is currently a paucity of research reports on the discovery of protease-producing microorganisms with industrial application value in the gut. Here, we employed microbial culturing to screen and identify the protease-producing microorganisms in the gut extract of Gryllotalpa orientalis. Based on morphological, physiological, and biochemical characterization, 16S rRNA sequencing, as well as ANI and dDDH values of whole genome, the protease-producing strains isolated from the insect gut were identified as Priestia aryahattai DBM-1 and DX-4, P. megaterium DX-3, and Serratia surfactantfaciens DBM-5. According to whole-genome analysis, strain DBM-5, which exhibited the highest enzyme activity, possesses abundant membrane transport genes and carbohydrate metabolism enzymes. In contrast, strains DX-3 and DX-4 not only have the ability to hydrolyze proteins but also demonstrate the capability to hydrolyze plant materials. Furthermore, strains that are closely related tend to have similar metabolic product gene clusters in their genomes. The screening and identification of protease resources are essential for the subsequent development and utilization of gut functional microorganisms and genetic resources in insects.

Gut microbiota diversity in a dung beetle (Catharsius molossus) across geographical variations and brood ball-mediated microbial transmission

The dung beetle primarily feeds on the feces of herbivorous animals and play a crucial role in ecological processes like material cycles and soil improvement. This study aims to explore the diversity and composition of the gut microbiota of Catharsius molossus (a renowned dung beetle originating from China and introduced to multiple countries for its ecological value) and exploring whether these gut microbes are transmitted vertically across generations. Using 16S rRNA and ITS rRNA gene sequencing techniques, we described the diversity and composition of gut microbes in C. molossus from different localities and different developmental stages (Egg, young larvae and old larvae). We discovered that the diversity of gut microbiota of dung beetles varied obviously among different geographical localities and different developmental stages, and we also discussed the potential influencing factors. Interestingly, the microbial community structure within the brood balls is more similar to male dung beetle than to that of females, which is consistent with the observation that the brood ball is constructed by the male dung beetle, with the female laying egg in it at the final step. This unique breeding method facilitates offspring in inheriting microbial communities from both the mother and the father. Initially, the larvae's gut microbiota closely mirrors that of the parental gift in these brood balls. As larvae grow, significant changes occur in their gut microbiota, including an increase in symbiotic bacteria like Lactococcus and Enterococcus. Analysis of the gut bacteria of adult dung beetles across various localities and different developmental stages identified nine core genera in adults, contributing to 67.80% of the total microbial abundance, and 11 core genera in beetles at different developmental stages, accounting for 49.13% of the total. Notably, seven genera were common between these two core groups. Our results suggest that Parental gifts can play a role in the vertical transmission of microbes, and the abundance of probiotics increases with larval development, supporting the hypothesis that "larval feeding behavior occurs in two stages: larvae first feed on parental gifts to acquire necessary microbes, then enrich symbiotic microbiota through consuming their own feces."

Changes in the bacterial communities of Harmonia axyridis (Coleoptera: Coccinellidae) in response to long-term cold storage and progressive loss of egg viability in cold-stored beetles

Bacteria have a profound influence on life history and reproduction of numerous insects, while the associations between hosts and bacteria are substantially influenced by environmental pressures. Cold storage is crucial for extending the shelf life of insects used as tools for biological control, but mostly causes detrimental effects. In this study, we observed a great decrease in egg hatch rate of cold-stored Harmonia axyridis during the later oviposition periods. Furthermore, most eggs produced by their F1 offspring exhibited complete loss of hatchability. We hypothesized that long-term exposure to cold may greatly alter the bacterial community within the reproductive tracts of H. axyridis, which may be an important factor contributing to the loss of egg viability. Through sequencing of the 16S rRNA gene, we discovered considerable changes in the bacterial structure within the reproductive tracts of female cold-stored beetles (LCS_F) compared to non-stored beetles (Control_F), with a notable increase in unclassified_f_Enterobacteriaceae in LCS_F. Furthermore, in accordance with the change of egg hatchability, we observed a slight variation in the microbial community of eggs produced by cold-stored beetles in early (Egg_E) and later (Egg_L) oviposition periods as well as in eggs produced by their F1 offspring (Egg_F1). Functional predictions of the microbial communities revealed a significant decrease in the relative abundance of substance dependence pathway in LCS_F. Moreover, this pathway exhibited relatively lower abundance levels in both Egg_L and Egg_F1 compared to Egg_E. These findings validate that long-term cold storage can greatly modify the bacterial composition within H. axyridis, thereby expanding our understanding of the intricate bacteria-insect host interactions.

Distinct gut microbial communities and functional predictions in divergent ophiuroid species: host differentiation, ecological niches, and adaptation to cold-water habitats

IMPORTANCE

Gastrointestinal microorganisms are critical to the survival and adaptation of hosts, and there are few studies on the differences and functions of gastrointestinal microbes in widely distributed species. This study investigated the gut microbes of two ophiuroid species (Ophiura sarsii and its subspecies O. sarsii vadicola) in cold-water habitats of the Northern Pacific Ocean. The results showed that a combination of host and environmental factors shapes the intestinal microbiota of ophiuroids. There was a high similarity in microbial communities between the two groups living in different regions, which may be related to their similar ecological niches. These microorganisms played a vital role in the ecological success of ophiuroids as the foundation for their adaptation to cold-water environments. This study revealed the complex relationship between hosts and their gut microbes, providing insights into the role they play in the adaptation and survival of marine species.

Spatial and Sexual Divergence of Gut Bacterial Communities in Field Cricket Teleogryllus occipitalis (Orthoptera: Gryllidae)

The insect gut is colonized by microbes that confer a myriad of beneficial services to the host, including nutritional support, immune enhancement, and even influence behavior. Insect gut microbes show dynamic changes due to the gut compartments, sex, and seasonal and geographic influences. Crickets are omnivorous hemimetabolous insects that have sex-specific roles, such as males producing chirping sounds for communication and exhibiting fighting behavior. However, limited information is available on their gut bacterial communities, hampering studies on functional compartmentalization of the gut and sex-specific roles of the gut microbiota in omnivorous insects. Here, we report a metagenomic analysis of the gut bacteriome of the field cricket Teleogryllus occipitalis using 16S rRNA V3-V4 amplicon sequencing to identify sex- and compartment-dependent influences on its diversity and function. The structure of the gut microbiota is strongly influenced by their gut compartments rather than sex. The species richness and diversity analyses revealed large difference in the bacterial communities between the gut compartments while minor differences were observed between the sexes. Analysis of relative abundance and predicted functions revealed that nitrogen- and oxygen-dependent metabolism and amino acid turnover were subjected to functional compartmentalization in the gut. Comparisons between the sexes revealed differences in the gut microbiota, reflecting efficiency in energy use, including glycolytic and carbohydrate metabolism, suggesting a possible involvement in egg production in females. This study provides insights into the gut compartment dependent and sex-specific roles of host-gut symbiont interactions in crickets and the industrial production of crickets.

Composition and diversity of gut microbiota across developmental stages of Spodoptera frugiperda and its effect on the reproduction

Introduction

Spodoptera frugiperda is a serious world-wide agricultural pest. Gut microorganisms play crucial roles in growth, development, immunity and behavior of host insects.

Methods

Here, we reported the composition of gut microbiota in a laboratory-reared strain of S. frugiperda using 16S rDNA sequencing and the effects of gut microbiota on the reproduction.

Results

Proteobacteria and Firmicutes were the predominant bacteria and the taxonomic composition varied during the life cycle. Alpha diversity indices indicated that the eggs had higher bacterial diversity than larvae, pupae and adults. Furthermore, eggs harbored a higher abundance of Ralstonia, Sediminibacterium and microbes of unclassified taxonomy. The dynamics changes in bacterial communities resulted in differences in the metabolic functions of the gut microbiota during development. Interestingly, the laid eggs in antibiotic treatment groups did not hatch much due to the gut dysbacteriosis, the results showed gut microbiota had a significant impact on the male reproduction.

Discussion

Our findings provide new perspectives to understand the intricate associations between microbiota and host, and have value for the development of S. frugiperda management strategies focusing on the pest gut microbiota.

Edible insects as emerging food products-processing and product development perspective

Edible insects (EI) are also becoming as a part of the diet due to their nutritional value and health benefits in many regions of the world. These EI are inexhaustible sources accessible by garnering from the wild with high feed conversion efficiency. Appreciating the budding of EI in justifiable food production, enlightening food security and biodiversity conversion, is promising a sufficient supply of the insect resource for future food to the world. These insects are processed to develop new products, improve organoleptic and nutritional parameters as well as the extension of shelf life. In this review, we discuss the edible insect characteristics, the potential application of EI in food industry, processing, pretreatments, drying, extraction of edible compounds like protein, lipid and chitin various food products formulation, safety regulation. Availability of broad nutritional spectrum of EI includes protein, mono and poly unsaturaturated fatty acids, amino acids, vitamins, amino aids and minerals has been used as an ingredient in development of various forms of food products such as flours in the form of whole insect powder, protein isolate, canned products, extruded products, hard candies, spreads, liquor infusion, cookies and other products.

Metabarcoding of fecal pellets in wild muskox populations reveals negative relationships between microbiome and diet alpha diversity

Microbiome diversity and diet composition concomitantly influence species health, fitness, immunity, and digestion. In environments where diet varies spatially and temporally, microbiome plasticity may promote rapid host adaptation to available resources. For northern ungulates in particular, metabarcoding of noninvasively collected fecal pellets presents unprecedented insights into their diverse ecological requirements and niches by clarifying the interrelationships of microbiomes, key to deriving nutrients, in context of altered forage availability in changing climates. Muskoxen (Ovibos moschatus) are Arctic-adapted species that experience fluctuating qualities and quantities of vegetation. Geography and seasonality have been noted to influence microbiome composition and diversity in muskoxen, yet it is unclear how their microbiomes intersect with diet. Following observations from other species, we hypothesized increasing diet diversity would result in higher microbiome diversity in muskoxen. We assessed diet composition in muskoxen using three common plant metabarcoding markers and explored correlations with microbiome data. Patterns of dietary diversity and composition were not fully concordant among the markers used, yet all reflected the primary consumption of willows and sedges. Individuals with similar diets had more similar microbiomes, yet in contrast to most literature, yielded negative relationships between microbiome and diet alpha diversity. This negative correlation may reflect the unique capacities of muskoxen to survive solely on high-fiber Arctic forage and provide insight into their resiliency to exploit changing dietary resources in a rapidly warming Arctic altering vegetation diversity.

Gut microbiota assemblages of generalist predators are driven by local- and landscape-scale factors

The gut microbiomes of arthropods have significant impact on key physiological functions such as nutrition, reproduction, behavior, and health. Spiders are diverse and numerically dominant predators in crop fields where they are potentially important regulators of pests. Harnessing spiders to control agricultural pests is likely to be supported by an understanding of their gut microbiomes, and the environmental drivers shaping microbiome assemblages. This study aimed to deciphering the gut microbiome assembly of these invertebrate predators and elucidating potential implications of key environmental constraints in this process. Here, we used high-throughput sequencing to examine for the first time how the assemblages of bacteria in the gut of spiders are shaped by environmental variables. Local drivers of microbiome composition were globally-relevant input use system (organic production vs. conventional practice), and crop identity (Chinese cabbage vs. cauliflower). Landscape-scale factors, proportion of forest and grassland, compositional diversity, and habitat edge density, also strongly affected gut microbiota. Specific bacterial taxa were enriched in gut of spiders sampled from different settings and seasons. These findings provide a comprehensive insight into composition and plasticity of spider gut microbiota. Understanding the temporal responses of specific microbiota could lead to innovative strategies development for boosting biological control services of predators.

Response of the Pardosa astrigera bacterial community to Cry1B protein

While genetically modified (GM) crops bring economic benefits to human beings, their impact on non-target organisms has become an important part of environmental safety assessments. Symbiotic bacteria play an important role in eukaryotic biological functions and can adjust host communities to adapt to new environments. Therefore, this study examined the effects of Cry1B protein on the growth and development of non-target natural enemies of Pardosa astrigera (L. Koch) from the perspective of symbiotic bacteria. Cry1B protein had no significant effect on the health indicators of P. astrigera (adults and 2nd instar spiderlings). 16S rRNA sequencing results revealed that Cry1B protein did not change the symbiotic bacteria species composition of P. astrigera, but did reduce the number of OTU and species diversity. In 2nd instar spiderlings, neither the dominant phylum (Proteobacteria) nor the dominant genus (Acinetobacter) changed, but the relative abundance of Corynebacterium-1 decreased significantly; in adult spiders, the dominant bacteria genera of females and males were different. The dominant bacterial genera were Brevibacterium in females and Corynebacterium-1 in males, but Corynebacterium-1 was the dominant bacteria in both females and males feeding on Cry1B. The relative abundance of Wolbachia also increased significantly. In addition, bacteria in other genera varied significantly by sex. KEGG results showed that Cry1B protein only altered the significant enrichment of metabolic pathways in female spiders. In conclusion, the effects of Cry1B protein on symbiotic bacteria vary by growth and development stage and sex.

Nutritional and reproductive status affect amino acid appetite in house crickets (Acheta domesticus)

We examined amino acid appetite in the omnivorous house cricket (Acheta domesticus), a common model organism for both research and teaching. Our first experiment addressed the hypothesis that house crickets can discriminate between sucrose and essential amino acids (EAA), and that preference for the latter would be affected by prior feeding experience. To test this hypothesis, we compared feeding responses of juvenile and adult crickets following pre-feeding with sucrose or an essential amino acid mixture, predicting that sucrose-only pre-feeding would enhance subsequent intake of amino acids in a two-choice preference test. Based on previous studies, we also predicted that amino acid consumption would be enhanced in females compared to males, and in mated compared to virgin females. Hence we compared responses in male and female last instar nymphs, adult males, virgin females, mated females, and mated females allowed to lay eggs. The second experiment examined how extended periods of essential amino acid deprivation (48 h to 6 days) affected appetite for these nutrients in adult male and female insects. Finally, we examined growth and survival of juvenile and adult crickets fed a holidic diet lacking all amino acids and protein. Our results demonstrated that house crickets can distinguish EAA from sucrose and that consumption of the former is enhanced following sucrose-only pre-feeding. We also found sex and developmental differences, with juvenile and virgin females showing a greater preference for EAA than juvenile or adult males. Contrary to expectation, mated females preferred sucrose over EAA both prior to and after egg laying. We also found that the crickets of both sexes increased their intake of EAA when exposed to longer periods of deprivation, indicating that they engage in compensatory feeding on these nutrients. Finally, as expected we found that growth was severely limited in juveniles fed a diet lacking all amino acids, but adults and many juveniles survived for 30 days on this diet.

Lack of host phylogenetic structure in the gut bacterial communities of New Zealand cicadas and their interspecific hybrids

Host-microbe interactions are intimately linked to eukaryotic evolution, particularly in sap-sucking insects that often rely on obligate microbial symbionts for nutrient provisioning. Cicadas (Cicadidae: Auchenorrhyncha) specialize on xylem fluid and derive many essential amino acids and vitamins from intracellular bacteria or fungi (Hodgkinia, Sulcia, and Ophiocordyceps) that are propagated via transmission from mothers to offspring. Despite the beneficial role of these non-gut symbionts in nutrient provisioning, the role of beneficial microbiota within the gut remains unclear. Here, we investigate the relative abundance and impact of host phylogeny and ecology on gut microbial diversity in cicadas using 16S ribosomal RNA gene amplicon sequencing data from 197 wild-collected cicadas and new mitochondrial genomes across 38 New Zealand cicada species, including natural hybrids between one pair of two species. We find low abundance and a lack of phylogenetic structure and hybrid effects but a significant role of elevation in explaining variation in gut microbiota.

Fruit fly phylogeny imprints bacterial gut microbiota

One promising avenue for reconciling the goals of crop production and ecosystem preservation consists in the manipulation of beneficial biotic interactions, such as between insects and microbes. Insect gut microbiota can affect host fitness by contributing to development, host immunity, nutrition, or behavior. However, the determinants of gut microbiota composition and structure, including host phylogeny and host ecology, remain poorly known. Here, we used a well-studied community of eight sympatric fruit fly species to test the contributions of fly phylogeny, fly specialization, and fly sampling environment on the composition and structure of bacterial gut microbiota. Comprising both specialists and generalists, these species belong to five genera from to two tribes of the Tephritidae family. For each fly species, one field and one laboratory samples were studied. Bacterial inventories to the genus level were produced using 16S metabarcoding with the Oxford Nanopore Technology. Sample bacterial compositions were analyzed with recent network-based clustering techniques. Whereas gut microbiota were dominated by the Enterobacteriaceae family in all samples, microbial profiles varied across samples, mainly in relation to fly identity and sampling environment. Alpha diversity varied across samples and was higher in the Dacinae tribe than in the Ceratitinae tribe. Network analyses allowed grouping samples according to their microbial profiles. The resulting groups were very congruent with fly phylogeny, with a significant modulation of sampling environment, and with a very low impact of fly specialization. Such a strong imprint of host phylogeny in sympatric fly species, some of which share much of their host plants, suggests important control of fruit flies on their gut microbiota through vertical transmission and/or intense filtering of environmental bacteria.

Natural diversity of the honey bee (Apis mellifera) gut bacteriome in various climatic and seasonal states

As pollinators and producers of numerous human-consumed products, honey bees have great ecological, economic and health importance. The composition of their bacteriota, for which the available knowledge is limited, is essential for their body's functioning. Based on our survey, we performed a metagenomic analysis of samples collected by repeated sampling. We used geolocations that represent the climatic types of the study area over two nutritionally extreme periods (March and May) of the collection season. Regarding bacteriome composition, a significant difference was found between the samples from March and May. The samples' bacteriome from March showed a significant composition difference between cooler and warmer regions. However, there were no significant bacteriome composition differences among the climatic classes of samples taken in May. Based on our results, one may conclude that the composition of healthy core bacteriomes in honey bees varies depending on the climatic and seasonal conditions. This is likely due to climatic factors and vegetation states determining the availability and nutrient content of flowering plants. The results of our study prove that in order to gain a thorough understanding of a microbiome's natural diversity, we need to obtain the necessary information from extreme ranges within the host's healthy state.

Effect of genetically modified maize expressing the Cry1Ab and EPSPS proteins on growth, development, and gut bacterial diversity of the non-target arthropod Locusta migratoria

The widespread cultivation of genetically modified (GM) crops has raised concerns for their safety. Here, we evaluated the effects of a GM maize variety expressing the Cry1Ab (14.76 ± 0.87 μg/g FW) and EPSPS proteins (191.55 ± 15.69 μg/g FW) on the life-history traits and gut bacterial community of a non-target arthropod, Locusta migratoria, in the laboratory. We found that GM maize had no significant effect on the survival or body weight of different development stages of L. migratoria. The midgut and hindgut bacterial diversities and compositions were determined using high-throughput sequencing targeting the V3-V4 regions of the 16S rRNA. No significant changes were found in the species diversity or abundance between insects in the GM-fed treatment and the non-GM control. Furthermore, the concentration of Cry1Ab and EPSPS in the gut was determined after digestion of GM maize. Results showed that the contents of Cry1Ab/EPSPS rapidly decreased and were hard to detect after 72 h. Based on the parameters assessed, we can conclude that the GM maize variety examined has no significant adverse effect on L. migratoria.

The Role of Feeding Characteristics in Shaping Gut Microbiota Composition and Function of Ensifera (Orthoptera)

Feeding habits were the primary factor affecting the gut bacterial communities in Ensifera. However, the interaction mechanism between the gut microbiota and feeding characteristics is not precisely understood. Here, the gut microbiota of Ensifera with diverse feeding habits was analyzed by shotgun metagenomic sequencing to further clarify the composition and function of the gut microbiota and its relationship with feeding characteristics. Our results indicate that under the influence of feeding habits, the gut microbial communities of Ensifera showed specific characteristics. Firstly, the gut microbial communities of the Ensifera with different feeding habits differed significantly, among which the gut microbial diversity of the herbivorous Mecopoda niponensis was the highest. Secondly, the functional genes related to feeding habits were in high abundance. Thirdly, the specific function of the gut microbial species in the omnivorous Gryllotalpa orientalis showed that the more diverse the feeding behavior of Ensifera, the worse the functional specificity related to the feeding characteristics of its gut microbiota. However, feeding habits were not the only factors affecting the gut microbiota of Ensifera. Some microorganisms' genes, whose functions were unrelated to feeding characteristics but were relevant to energy acquisition and nutrient absorption, were detected in high abundance. Our results were the first to report on the composition and function of the gut microbiota of Ensifera based on shotgun metagenomic sequencing and to explore the potential mechanism of the gut microbiota's association with diverse feeding habits.

Characterization of Microbial Communities from the Alimentary Canal of Typhaea stercorea (L.) (Coleoptera: Mycetophagidae)

Simple Summary

Hairy fungus beetle, Typhaea stercorea, is a secondary post-harvest pest of stored grains that thrives by feeding on mytoxigenic fungi. Bacterial communities residing in the alimentary canal of most insects contribute to their host’s development. While there are many examples, little is known about the role of bacterial communities in the alimentary canal of T. stercorea. The objectives of this study were to (1) characterize the microbial communities residing in T. stercorea and (2) compare the microbial compositions of field-collected and laboratory-reared populations. In this study, we were able to identify bacterial communities that possess mycolytic properties and track mark changes in the microbiota profiles associated with development. The genus Pseudomonas was enriched in T. stercorea larvae compared to adults. Furthermore, field-collected T. sterocrea adults had a lower species richness than both larva and adult laboratory-reared T. sterocrea. Moreover, the gut microbial compositions of field-collected and laboratory-reared populations were vastly different. Overall, our results suggest that the environment and physiology can shift the microbial composition in the alimentary canal of T. stercorea.

Abstract

The gut microbiomes of symbiotic insects typically mediate essential functions lacking in their hosts. Here, we describe the composition of microbes residing in the alimentary canal of the hairy fungus beetle, Typhaea stercorea (L.), at various life stages. This beetle is a post-harvest pest of stored grains that feeds on fungi and serves as a vector of mycotoxigenic fungi. It has been reported that the bacterial communities found in most insects’ alimentary canals contribute to nutrition, immune defenses, and protection from pathogens. Hence, bacterial symbionts may play a key role in the digestive system of T. stercorea. Using 16S rRNA amplicon sequencing, we examined the microbiota of T. stercorea. We found no difference in bacterial species richness between larvae and adults, but there were compositional differences across life stages (PERMANOVA:pseudo-F_(8,2) = 8.22; p = 0.026). The three most abundant bacteria found in the alimentary canal of the larvae and adults included Pseudomonas (47.67% and 0.21%, respectively), an unspecified genus of the Enterobacteriaceae family (46.60 % and 90.97%, respectively), and Enterobacter (3.89% and 5.75%, respectively). Furthermore, Pseudomonas spp. are the predominant bacteria in the larval stage. Our data indicated that field-collected T. stercorea tended to have lower species richness than laboratory-reared beetles (Shannon: H = 5.72; p = 0.057). Furthermore, the microbial communities of laboratory-reared insects resembled one another, whereas field-collected adults exhibited variability (PERMANOVA:pseudo-F_(10,3) = 4.41; p = 0.006). We provide evidence that the environment and physiology can shift the microbial composition in the alimentary canal of T. stercorea.

Exploring the gut microbiota composition of Indian major carp, rohu (Labeo rohita), under diverse culture conditions

Gut microbiota of freshwater carps are often investigated for their roles in nutrient absorption, enzyme activities and probiotic properties. However, little is known about core microbiota, assembly pattern and the environmental influence on the gut microbiota of the Indian major carp, rohu. The gut microbial composition of rohu reared in different culture conditions was analysed by 16S rRNA amplicon sequencing. There was variation on gut microbial diversity and composition. A significant negative correlation between dissolved oxygen content (DO) and alpha diversity was observed, thus signifying DO content as one of the key environmental factors that regulated the diversity of rohu gut microbial community. A significant positive correlation was observed between phosphate concentration and abundance of Actinobacteria in different culture conditions. Two phyla, Proteobacteria and Actinobacteria along with OTU750868 (Streptomyces) showed significant (p < 0.05) differences in their abundance among all culture conditions. The Non-metric multidimensional scaling ordination (NMDS) analysis using Bray-Curtis distances, showed the presence of unique gut microbiota in rohu compared to other herbivorous fish. Based on niche breadth, 3 OTUs were identified as core generalists, persistent across all the culture conditions whereas the specialists dominated in the rohu gut microbiota assembly. Co-occurrence network analysis revealed positive interaction within core members while mutual exclusion between core and non-core members. Predicted microbiota function revealed that different culture conditions affected the metabolic capacity of gut microbiota of rohu. The results overall indicated the significant effect of different rearing environments on gut microbiota structure, assembly and inferred community function of rohu which might be useful for effective manipulation of gut microbial communities of rohu to promote better health and growth under different husbandry settings.

Divergence in gut bacterial community between females and males in the wolf spider Pardosa astrigera

Sex is one of the important factors affecting gut microbiota. As key predators in agroforestry ecosystem, many spider species show dramatically different activity habits and nutritional requirements between females and males. However, how sex affects gut microbiota of spiders remains unclear. Here, we compared the composition and diversity of gut bacteria between female and male Pardosa astrigera based on bacterial 16S rRNA gene sequencing. Results showed that the richness of bacterial microbiota in female spiders was significantly lower than in male spiders (p < .05). Besides, β‐diversity showed a significant difference between female and male spiders (p = .0270). The relative abundance of Actinobacteriota and Rhodococcus (belongs to Actinobacteriota) was significantly higher in female than in male spiders (p < .05), whereas the relative abundance of Firmicutes and Acinetobacter (belongs to Proteobacteria) and Ruminococcus and Fusicatenibacter (all belong to Firmicutes) was significantly higher in male than in female spiders (p < .05). The results also showed that amino acid and lipid metabolisms were significantly higher in female than in male spiders (p < .05), whereas glycan biosynthesis and metabolism were significantly higher in male than in female spiders (p < .05). Our results imply that sexual variation is a crucial factor in shaping gut bacterial community in P. astrigera spiders, while the distinct differences of bacterial composition are mainly due to their different nutritional and energy requirements.

Review: Trait plasticity during plant-insect interactions: From molecular mechanisms to impact on community dynamics

Phenotypic plasticity, prevalent in all domains of life, enables organisms to cope with unpredictable or novel changes in their growing environment. Plants represent an interesting example of phenotypic plasticity which also directly represents and affects the dynamics of biological interactions occurring in a community. Insects, which interact with plants, manifest phenotypic plasticity in their developmental, physiological, morphological or behavioral traits in response to the various host plant defenses induced upon herbivory. However, plant-insect interactions are generally more complex and multidimensional because of their dynamic association with their respective microbiomes and macrobiomes. Moreover, these associations can alter plant and insect responses towards each other by modulating the degree of phenotypic plasticity in their various traits and studying them will provide insights into how plants and insects reciprocally affect each other's evolutionary trajectory. Further, we explore the consequences of phenotypic plasticity on relationships and interactions between plants and insects and its impact on their development, evolution, speciation and ecological organization. This overview, obtained after exploring and comparing data obtained from several inter-disciplinary studies, reveals how genetic and molecular mechanisms, underlying plasticity in traits, impact species interactions at the community level and also identifies mechanisms that could be exploited in breeding programs.

Dietary Effects on Biological Parameters and Gut Microbiota of Harmonia axyridis

The multicolored Asian lady beetle (Harmonia axyridis, H. axyridis, Coleoptera, and Coccinellidae) is an effective biocontrol agent against agricultural pests. Previous studies have suggested that amount, type, and the quality of food can directly affect the biological aspects of H. axyridis. In this study, we investigated the influence of the food sources (Acyrthosiphon pisum Harris, Diaphorina citri Kuwayama, and artificial diets) on the gut microbiota diversity and the biology, reproductive variables, and population growth indicators of H. axyridis. Three kinds of diets were considered in this study: (1) HY: the adult of A. pisum Harris (HY group); (2) HM: the adult of D. citri Kuwayama (HM group); (3) HR: artificial diets prepared by blending a portion of fresh homogenized pork liver (15 g), honey (3 g), distilled water (35 ml) (HR group). We found that gut microbiota composition and diversity and the biological parameters differed when H. axyridis was fed with different diets. The abundance of Enterobacteriaceae was the highest in the HM group, followed by HY group, and was the lowest in the HR group. The abundance of Staphylococcaceae was highest in the HR group. Among the gut fungi, Davidiellaceae and Wallemiaceae were the highest and lowest in the HY group; Incertae_sedis were the major gut fungi in the HR group. Meanwhile, the changes of biological parameters may be correlated with the changes of Streptococcaceae abundance, Micrococcaceae abundance, Staphylococcaceae abundance, and Enterobacteriaceae abundance in responds to diet changes. To sum up, these data suggest that different diets can influence the changes in adult H. axyridis gut microbiota, consequently affecting the biological parameters.

Novel Linkages Between Bacterial Composition of Hindgut and Host Metabolic Responses to SARA Induced by High-Paddy Diet in Young Goats

At present, feeding a high-corn diet to goats is used to provide enough protein and energy supply to meet their higher dietary requirements. In fact, because corn grain is commonly scarce in the traditional rice cropping region of southern Asia, paddy is thereby used as an alternative feed applied in goat diets. However, the effects of the high paddy proportion on the microbiota and metabolites of the intestine are unclear. Here, we investigate the effects of high paddy proportion on bacterial community, potential function, and metabolic reaction in the cecum of goats. Sixteen Liuyang black goats were divided into two groups fed either a normal-paddy (NP) diet (55% concentrate) or a high-paddy (HP) diet (90% concentrate) for 5 weeks. Total short-chain fatty acid (SCFA) concentration was higher in the hindgut chyme of the HP-fed goats than in that of the NP-fed goats (p = 0.001). The acetic proportion was significantly decreased and the propionic proportion was increased in the HP group (p &lt; 0.05). The HP diet decreased the value of pH, lactic acid concentration, and lactate dehydrogenase activity but increased the activity of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and amylase, together with lipopolysaccharide concentration in the hindgut chyme of goats (p &lt; 0.05). The abundance rates of the Eubacterium_coprostanoligenes_group was increased (p = 0.050), whereas the abundance of Prevotellaceae_UCG_004, dgA-11_gut_group, Christensenellaceae_R-7_group, Ruminococcaceae_UCG-010, and Desulfovibrio were significantly decreased with the HP diet (p &lt; 0.05). These results suggested that the HP diet altered the microbiota and metabolites, which negatively modified intestinal epithelial health in goats.

Microbial influence on reproduction, conversion, and growth of mass produced insects

One important feature of insect rearing is its apparent, and sometimes non-apparent, reliance on the bacterial ecosystem. Indeed, microbes contribute to insect nutrition, protection against natural enemies, and detoxification of dietary compounds, antibiotics, and insecticides. Further, microbes have been implicated as the source of signals and cues important to insect communication. But the incidence and general significance of these functions is only just being explored in the context of mass production of insects. Knowledge of the diversity and functional distribution of these microorganisms in mass-rearing systems is key to understanding microbial dynamics and to enhance system performance. Therefore, this brief review is a synthesis of literature surrounding insect rearing systems for the primary insects reared as food and feed (i.e. black soldier fly, Hermetia illucens (Diptera: Stratiomyidae), mealworms (Coleoptera: Tenebrionidae), and cricket (Orthoptera: Grylloidea) with a focus on recent advances pertaining to microbial contribution to reproduction, growth, and waste conversion.

Evaluation of Sample Preservation Approaches for Better Insect Microbiome Research According to Next-Generation and Third-Generation Sequencing

The microbial communities associated with insects play critical roles in many physiological functions such as digestion, nutrition, and defense. Meanwhile, with the development of sequencing technology, more and more studies begin to focus on broader biodiversity of insects and the corresponding mechanisms of insect microbial symbiosis, which need longer time collecting in the field. However, few studies have evaluated the effect of insect microbiome sample preservation approaches especially in different time durations or have assessed whether these approaches are appropriate for both next-generation sequencing (NGS) and third-generation sequencing (TGS) technologies. Here, we used Tessaratoma papillosa (Hemiptera: Tessaratomidae), an important litchi pest, as the model insect and adopted two sequencing technologies to evaluate the effect of four different preservation approaches (cetyltrimethylammonium bromide (CTAB), ethanol, air dried, and RNAlater). We found the samples treated by air dried method, which entomologists adopted for morphological observation and classical taxonomy, would get worse soon. RNAlater as the most expensive approaches for insect microbiome sample preservation did not suit for field works longer than 1 month. We recommended CTAB and ethanol as better preservatives in longer time field work for their effectiveness and low cost. Comparing with the full-length 16S rRNA gene sequenced by TGS, the V4 region of 16S rRNA gene sequenced by NGS has a lower resolution trait and may misestimate the composition of microbial communities. Our results provided recommendations for suitable preservation approaches applied to insect microbiome studies based on two sequencing technologies, which can help researchers properly preserve samples in field works.

The structure of the cereal leaf beetle (Oulema melanopus) microbiome depends on the insect's developmental stage, host plant, and origin

Cereal leaf beetle (CLB, Oulema melanopus, Coleoptera, Chrysomelidae) is a serious agricultural pest that causes considerable damages to agricultural production. The aim of this study was to characterize the bacterial communities associated with larvae and imagoes of CLB collected from various cereal host species and locations. The bacterial profile was characterized by 16S rRNA gene sequencing at the V3-V4 hypervariable region. Using taxonomy-based analysis, the bacterial community of CLB containing 16 phyla, 26 classes, 49 orders, 78 families, 94 genera, and 63 species of bacteria was identified. The abundance of Wolbachia, Rickettsia, and Lactococcus genus was significantly higher in CLB imagoes than in larvae. Statistical analysis confirmed that the bacterial community of the larvae is more diverse in comparison to imagoes and that insects collected from spring barley and wheat are characterized by a much higher biodiversity level of bacterial genera and species than insects collected from other cereals. Obtained results indicated that the developmental stage, the host plant, and the insect's sampling location affected the CLB's microbiome. Additionally, the CLB core microbiome was determined. It consists of 2 genera (Wolbachia and Rickettsia) shared by at least 90% tested CLB insects, regardless of the variables analysed.

Microbiome-Metabolites Analysis Reveals Unhealthy Alterations in the Gut Microbiota but Improved Meat Quality with a High-Rice Diet Challenge in a Small Ruminant Model

Simple Summary

Effects of a high-rice dietary proportion on the meat quality, gut microbiota and metabolites in small ruminants are rarely reported. Thus, the objective of this study was to evaluate the slaughtering characteristic and meat quality, acute phase reaction proteins (APRPs) in plasma and colonic microbiota and metabolites of goats subjected to a high-rice diet. After a 35-day period, sixteen goats received a high-rice diet (HR, 90% concentrate) or a control diet (55% concentrate). In summary, the results showed that the slaughter performance and meat quality were improved in the growing goats after being fed the HR diet. However, the HR diet induced an acute phase reaction and disturbed the gut microbiota to some extent, which increases the health risk to growing goats.

Abstract

Effects of a high-rice dietary proportion on the meat quality, acute phase reaction proteins (APRPs) and colonic microbiota and metabolites in goats are rarely reported. This study was designed to investigate the meat quality and metabolism in goats. Sixteen goats were equally divided into two groups and fed a control diet (Con, 55% concentrate) or a high-rice diet (HR, 90% concentrate) for five weeks. We found that the HR diet improved the slaughtering characteristic and meat quality but induced an acute phase reaction and decreased bacterial richness and diversity when compared to the control group. Furthermore, the levels of acetate, propionate and total VFA concentrations were higher in the colonic contents of the HR-fed goats than in those of the control group (p < 0.05). Meanwhile, the HR diet decreased the pH value, lactic acid concentration and increased the activity of amylase and lipopolysaccharide concentration in the colonic contents of goats (p < 0.05). The proportion of Oscillibacter increased while Phocaeicola and Christensenellaceae_R-7_group significantly decreased with the HR diet (p < 0.05). Collectively, the HR diet induced an acute phase reaction and altered the colonic bacterial community, which increases the health risk to growing goats.

The Gut Microbiota of Naturally Occurring and Laboratory Aquaculture Lytechinus variegatus Revealed Differences in the Community Composition, Taxonomic Co-Occurrence, and Predicted Functional Attributes

Sea urchins, in many instances, are collected from the wild, maintained in the laboratory aquaculture environment, and used as model animals for various scientific investigations. It has been increasingly evident that diet-driven dysbiosis of the gut microbiome could affect animal health and physiology, thereby impacting the outcome of the scientific studies. In this study, we compared the gut microbiome between naturally occurring (ENV) and formulated diet-fed laboratory aquaculture (LAB) sea urchin Lytechinus variegatus by amplicon sequencing of the V4 region of the 16S rRNA gene and bioinformatics tools. Overall, the ENV gut digesta had higher taxa richness with an abundance of Propionigenium, Photobacterium, Roseimarinus, and Flavobacteriales. In contrast, the LAB group revealed fewer taxa richness, but noticeable abundances of Arcobacter, Agarivorans, and Shewanella. However, Campylobacteraceae, primarily represented by Arcobacter spp., was commonly associated with the gut tissues of both ENV and LAB groups whereas the gut digesta had taxa from Gammaproteobacteria, particularly Vibrio spp. Similarly, the co-occurrence network displayed taxonomic organizations interconnected by Arcobacter and Vibrio as being the key taxa in gut tissues and gut digesta, respectively. Predicted functional analysis of the gut tissues microbiota of both ENV and LAB groups showed a higher trend in energy-related metabolisms, whereas amino acids, carbohydrate, and lipid metabolisms heightened in the gut digesta. This study provides an outlook of the laboratory-formulated diet-fed aquaculture L. variegatus gut microbiome and predicted metabolic profile as compared to the naturally occurring animals, which should be taken into consideration for consistency, reproducibility, and translatability of scientific studies.

Interkingdom Gut Microbiome and Resistome of the Cockroach Blattella germanica

Cockroaches are intriguing animals with two coexisting symbiotic systems, an endosymbiont in the fat body, involved in nitrogen metabolism, and a gut microbiome whose diversity, complexity, role, and developmental dynamics have not been fully elucidated. In this work, we present a metagenomic approach to study Blattella germanica populations not treated, treated with kanamycin, and recovered after treatment, both naturally and by adding feces to the diet, with the aim of better understanding the structure and function of its gut microbiome along the development as well as the characterization of its resistome.IMPORTANCE For the first time, we analyze the interkingdom hindgut microbiome of this species, including bacteria, fungi, archaea, and viruses. Network analysis reveals putative cooperation between core bacteria that could be key for ecosystem equilibrium. We also show how antibiotic treatments alter microbiota diversity and function, while both features are restored after one untreated generation. Combining data from B. germanica treated with three antibiotics, we have characterized this species' resistome. It includes genes involved in resistance to several broad-spectrum antibiotics frequently used in the clinic. The presence of genetic elements involved in DNA mobilization indicates that they can be transferred among microbiota partners. Therefore, cockroaches can be considered reservoirs of antibiotic resistance genes (ARGs) and potential transmission vectors.

Gut bacterial communities across 12 Ensifera (Orthoptera) at different feeding habits and its prediction for the insect with contrasting feeding habits

Insect microbial symbioses play a critical role in insect lifecycle, and insect gut microbiome could be influenced by many factors. Studies have shown that host diet and taxonomy have a strong influence on insect gut microbial community. In this study, we performed sequencing of V3-V4 region of 16S rRNA gene to compare the composition and diversity of 12 Ensifera from 6 provinces of China. Moreover, the influences of feeding habits and taxonomic status of insects on their gut bacterial community were evaluated, which might provide reference for further application research. The results showed that Proteobacteria (45.66%), Firmicutes (34.25%) and Cyanobacteria (7.7%) were the predominant bacterial phyla in Ensifera. Moreover, the gut bacterial community composition of samples with different feeding habits was significantly different, which was irrespective of their taxa. The highest diversity of gut bacteria was found in the omnivorous Ensifera. Furthermore, common and unique bacteria with biomarkers were found based on the dietary characteristics of the samples. However, the bacterial community structure of the Ensifera samples was significantly different from that of Caelifera. Therefore, we concluded that feeding habits and taxonomic status jointly affect the gut bacterial community composition of the samples from Orthoptera. However, the influence of feeding habit dominates when taxonomy category below the suborder level. In addition, the dominant, common and unique bacterial community structure could be used to predict the contrastic feeding habits of insects belonging to Ensifera.

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.

Divergence in Gut Bacterial Community Structure between Male and Female Stag Beetles Odontolabis fallaciosa (Coleoptera, Lucanidae)

Simple Summary

Intestinal microbiota play crucial roles for their hosts. Odontolabis fallaciosa shows striking sexual dimorphism and male trimorphism, which represents an interesting system to study their gut microbiota. We have compared the intestinal bacterial community structure between the two sexes and among three male morphs of O. fallaciosa. The gut bacterial community structure was significantly different between males and females. The females were associated with higher bacterial alpha-diversity relative to males. Large males had a higher relative abundance of Firmicutes and Firmicutes/Bacteroides (F/B) ratio, which contributed to nutritional efficiency. The results increased our understanding of beetle–bacterial interactions of O. fallaciosa between the two sexes, and among three male morphs, which might reveal the relationship among the gut microbiota, nutrition level, and phenotypic evolution of the stag beetle.

Abstract

Odontolabis fallaciosa (Coleoptera: Lucanidae) is a giant and popular stag beetle with striking sexual dimorphism and male trimorphism. However, little is known about their intestinal microbiota, which might play an indispensable role in shaping the health of their hosts. The aim of this study was to investigate the intestinal bacterial community structure between the two sexes and among three male morphs of O. fallaciosa from China using high-throughput sequencing (Illumina MiSeq). The gut bacterial community structure was significantly different between males and females, suggesting that sex appeared to be the crucial factor shaping the intestinal bacterial community. Females had higher bacterial alpha-diversity than males. There was little difference in gut bacterial community structure among the three male morphs. However, compared to medium and small males, large individuals were associated with the higher relative abundance of Firmicutes and Firmicutes/Bacteroides (F/B) ratio, which might contribute to nutritional efficiency. Overall, these results might help to further our understanding of beetle–bacterial interactions of O. fallaciosa between the two sexes, and among the three male morphs.

Diversity and Composition of the Gut Microbiota in the Developmental Stages of the Dung Beetle Copris incertus Say (Coleoptera, Scarabaeidae)

Dung beetles are holometabolous insects that feed on herbivorous mammal dung and provide services to the ecosystem including nutrient cycling and soil fertilization. It has been suggested that organisms developing on incomplete diets such as dungs require the association with microorganisms for the synthesis and utilization of nutrients. We describe the diversity and composition of the gut-microbiota during the life cycle of the dung beetle Copris incertus using 16S rRNA gene sequencing. We found that C. incertus gut contained a broad diversity of bacterial groups (1,699 OTUs and 302 genera). The taxonomic composition varied during the beetle life cycle, with the predominance of some bacterial genera in a specific developmental stage (Mothers: Enterobacter and Serratia; Eggs: Nocardioides and Hydrogenophaga; Larval and pupal stages: Dysgonomonas and Parabacteroides; offspring: Ochrobactrum). The beta diversity evidenced similarities among developmental stages, clustering (i) the adult stages (mother, male and female offsprings), (ii) intermediate developmental (larvae and pupa), and (iii) initial stage (egg). Microbiota differences could be attributed to dietary specialization or/and morpho-physiological factors involved in the transition from a developmental stage to the next. The predicted functional profile (PICRUSt2 analysis) for the development bacterial core of the level 3 categories, indicated grouping by developmental stage. Only 36 categories were significant in the SIMPER analysis, including the metabolic categories of amino acids and antibiotic synthesis, which were enriched in the larval and pupal stages; both categories are involved in the metamorphosis process. At the gene level, we found significant differences only in the KOs encoding functions related to nitrogen fixation, uric acid metabolism, and plant cell wall degradation for all developmental stages. Nitrogen fixation and plant cell wall degradation were enriched in the intermediate stages and uric acid metabolism was enriched in mothers. The data reported here suggested the influence of the maternal microbiota in the composition and diversity of the gut microbiota of the offspring.

Captivity affects diversity, abundance, and functional pathways of gut microbiota in the northern grass lizard Takydromus septentrionalis

Animals in captivity undergo a range of environmental changes from wild animals. An increasing number of studies show that captivity significantly affects the abundance and community structure of gut microbiota. The northern grass lizard (Takydromus septentrionalis) is an extensively studied lacertid lizard and has a distributional range covering the central and southeastern parts of China. Nonetheless, little is known about the gut microbiota of this species, which may play a certain role in nutrient and energy metabolism as well as immune homeostasis. Here, we examined the differences in the gut microbiota between two groups (wild and captive) of lizards through 16S rRNA sequencing using the Illumina HiSeq platform. The results demonstrated that the dominant microbial components in both groups consisted of Proteobacteria, Firmicutes, and Tenericutes. The two groups did not differ in the abundance of these three phyla. Citrobacter was the most dominant genus in wild lizards, while Morganella was the most dominant genus in captive lizards. Moreover, gene function predictions showed that genes at the KEGG pathway levels2 were more abundant in wild lizards than in captive lizards but, at the KEGG pathway levels1, the differences in gene abundances between wild and captive lizards were not significant. In summary, captivity exerted a significant impact on the gut microbial community structure and diversity in T. septentrionalis, and future work could usefully investigate the causes of these changes using a comparative approach.

Dynamics of Insect-Microbiome Interaction Influence Host and Microbial Symbiont

Insects share an intimate relationship with their gut microflora and this symbiotic association has developed into an essential evolutionary outcome intended for their survival through extreme environmental conditions. While it has been clearly established that insects, with very few exceptions, associate with several microbes during their life cycle, information regarding several aspects of these associations is yet to be fully unraveled. Acquisition of bacteria by insects marks the onset of microbial symbiosis, which is followed by the adaptation of these bacterial species to the gut environment for prolonged sustenance and successful transmission across generations. Although several insect-microbiome associations have been reported and each with their distinctive features, diversifications and specializations, it is still unclear as to what led to these diversifications. Recent studies have indicated the involvement of various evolutionary processes operating within an insect body that govern the transition of a free-living microbe to an obligate or facultative symbiont and eventually leading to the establishment and diversification of these symbiotic relationships. Data from various studies, summarized in this review, indicate that the symbiotic partners, i.e., the bacteria and the insect undergo several genetic, biochemical and physiological changes that have profound influence on their life cycle and biology. An interesting outcome of the insect-microbe interaction is the compliance of the microbial partner to its eventual genome reduction. Endosymbionts possess a smaller genome as compared to their free-living forms, and thus raising the question what is leading to reductive evolution in the microbial partner. This review attempts to highlight the fate of microbes within an insect body and its implications for both the bacteria and its insect host. While discussion on each specific association would be too voluminous and outside the scope of this review, we present an overview of some recent studies that contribute to a better understanding of the evolutionary trajectory and dynamics of the insect-microbe association and speculate that, in the future, a better understanding of the nature of this interaction could pave the path to a sustainable and environmentally safe way for controlling economically important pests of crop plants.

Development of fly tolerance to consuming a high-protein diet requires physiological, metabolic and transcriptional changes

Mortality in insects consuming high-protein-and-low-carbohydrate diets resembles a type III lifespan curve with increased mortality at an early age and few survivors that live a relatively long lifespan. We selected for a Drosophila line able to live for a long time on an imbalanced high-protein-low-carbohydrate diet by carrying out five rounds of breeding to select for the most long-lived survivors. Adaptation to this diet in the selected line was studied at the biochemical, physiological and transcriptomic levels. The selected line of flies consumed less of the imbalanced food but also accumulated more storage metabolites: glycogen, triacylglycerides, and trehalose. Selected flies also had a higher activity of alanine transaminase and a higher urea content. Adaptation of the selected line on the transcriptomic level was characterized by down-regulation of genes encoding serine endopeptidases (Jon25i, Jon25ii, betaTry, and others) but up-regulation of genes encoding proteins related to the immune system, such as antimicrobial peptides, Turandot-family humoral factors, hexamerin isoforms, and vitellogenin. These sets of down- and up-regulated genes were similar to those observed in fruit flies with suppressed juvenile hormone signaling. Our data show that the physiological adaptation of fruit flies to a high-protein-low-carbohydrate diet occurs via intuitive pathways, namely a decrease in food consumption, conversion of amino acids into ketoacids to compensate for the lack of carbohydrate, and accumulation of storage metabolites to eliminate the negative effects of excess amino acids. Nevertheless, transcriptomic adaptation occurs in a counter-intuitive way likely via an influence of gut microbiota on food digestion.

Structure and membership of gut microbial communities in multiple fish cryptic species under potential migratory effects

The animal gut microbiota evolves quickly towards a complex community and plays crucial roles in its host’s health and development. Factors such as host genetics and environmental changes are regarded as important for controlling the dynamics of animal gut microbiota. Migratory animals are an important group for studying how these factors influence gut microbiota because they experience strong environmental perturbations during migration. The commercially important grey mullet, Mugil cephalus, is a cosmopolitan species complex that display reproductive migration behaviour. There are three cryptic species of M. cephalus fish distributed across the Northwest Pacific, and their spawning sites overlap in the Taiwan Strait. This extraordinary natural occurrence makes the grey mullet an ideal model organism for exploring the nature of wild animal-gut microbiota relationships and interactions. This study investigates the diversity and structure of the gut microbial community in three cryptic M. cephalus species using 16S rRNA amplicon sequencing. Gut microbial compositions from adult and juvenile fish samples were analysed. Our results indicate that gut microbial communities within the grey mullet share a core microbiome dominated by Proteobacteria, Firmicutes and Actinobacteria. However, the structures of gut microbial communities were more distinct between adult mullet groups than they were between juvenile ones. Intriguingly, we found that adult fish that migrate to different geographical tracts harbour gut microbiota similar to historical records of seawater microflora, along their respective migration routes. This observation provides new insights into the interaction between aquatic animal gut microbial communities and the environments along their hosts’ migratory routes, and thus warrants future study.

New Insights Into Culturable and Unculturable Bacteria Across the Life History of Medicinal Maggots Lucilia sericata (Meigen) (Diptera: Calliphoridae)

Because of the nutritional ecology of dung- and carrion-feeding, bacteria are the integral part of Lucilia sericata life cycle. Nevertheless, the disinfected larvae of the blowfly are applied to treat human chronic wounds in a biosurgery named maggot debridement therapy (MDT). To realize the effects of location/diet on the gut bacteria, to infer the role of bacteria in the blowfly ecology plus in the MDT process, and to disclose bacteria circulating horizontally in and vertically between generations, bacterial communities associated with L. sericata specimens from various sources were investigated using culture-based and culture-independent methods. In total, 265 bacteria, including 20 families, 28 genera, and 40 species, were identified in many sources of the L. sericata. Culture-dependent method identified a number of 144 bacterial isolates, including 21 species, in flies reared in an insectary; specimens were collected from the field, and third-instar larvae retrieved from chronic wounds of patients. Metagenetic approach exposed the occurrences of 121 operational taxonomic units comprising of 32 bacterial species from immature and adult stages of L. sericata. Gammaproteobacteria was distinguished as the dominant class of bacteria by both methods. Bacteria came into the life cycle of L. sericata over the foods and transovarially infected eggs. Enterococcus faecalis, Myroides phaeus, Proteus species, Providencia vermicola, and Serratia marcescens were exchanged among individuals via transstadial transmission. Factors, including diets, feeding status, identification tool, gut compartment, and life stage, governed the bacteria species. Herein, we reemphasized that L. sericata is thoroughly connected to the bacteria both in numerous gut compartments and in different life stages. Among all, transstadially transmitted bacteria are underlined, indicating the lack of antagonistic effect of the larval excretions/secretions on these resident bacteria. While the culture-dependent method generated useful data on the viable aerobic gut bacteria, metagenomic method enabled us to identify bacteria directly from the tissues without any need for cultivation and to facilitate the identification of anaerobic and unculturable bacteria. These findings are planned to pave the way for further research to determine the role of each bacterial species/strain in the insect ecology, as well as in antimicrobial, antibiofilm, anti-inflammatory, and wound healing activities.

Probiotic effects of mixture of Groenewaldozyma salmanticensis and Gluconacetobacter liquefaciens on growth and immune responses in Paralichthys olivaceus

This study was performed to evaluate the effects of dietary probiotics on growth, non-specific immune responses and disease resistance in olive flounder, Paralichthys olivaceus. During 8 weeks, the fish were fed the five experimental diets such as a basal commercial diet (CON), oxytetracycline (OTC) and three basal diets containing Bacillus subtilis (BS), a commercial microbial product (CES) and a mixture of yeast and bacterium (PI), respectively. Fish fed all the probiotics diets and OTC showed a significantly higher growth than fish-fed CON (P < 0·05). Fish-fed PI had a significantly higher nitroblue tetrazolium activity, whereas fish-fed CES showed a higher lysozyme level (P < 0·05). A 7-day challenge test also showed that fish-fed PI had a cumulative survival rate equivalent to that of fish-fed OTC (P < 0·05). Moreover, the diet (PI) appeared to increase the diversity of microbial community in the fish. All these results suggest that the probiotics diet could function as a potential antibiotic replacer in the olive flounder. SIGNIFICANCE AND IMPACT OF THE STUDY: This study is unique in revealing that a diet mixture of yeast, Groenewaldozyma salmanticensis and bacterium Gluconacetobacter liquefaciens can enhance growth, innate immunity and diversity of microbial community including dominant species in the olive flounder. All these indicate that the diet mixture could function as a potential antibiotic replacer in one of the most commercially important fisheries in South Korea.

Are you what you eat? A highly transient and prey-influenced gut microbiome in the grey house spider Badumna longinqua

Stable core microbial communities have been described in numerous animal species and are commonly associated with fitness benefits for their hosts. Recent research, however, highlights examples of species whose microbiota are transient and environmentally derived. Here, we test the effect of diet on gut microbial community assembly in the spider Badumna longinqua. Using 16S rRNA gene amplicon sequencing combined with quantitative PCR, we analyzed diversity and abundance of the spider's gut microbes, and simultaneously characterized its prey communities using nuclear rRNA markers. We found a clear correlation between community similarity of the spider's insect prey and gut microbial DNA, suggesting that microbiome assembly is primarily diet-driven. This assumption is supported by a feeding experiment, in which two types of prey-crickets and fruit flies-both substantially altered microbial diversity and community similarity between spiders, but did so in different ways. After cricket consumption, numerous cricket-derived microbes appeared in the spider's gut, resulting in a rapid homogenization of microbial communities among spiders. In contrast, few prey-associated bacteria were detected after consumption of fruit flies; instead, the microbial community was remodelled by environmentally sourced microbes, or abundance shifts of rare taxa in the spider's gut. The reshaping of the microbiota by both prey taxa mimicked a stable core microbiome in the spiders for several weeks post feeding. Our results suggest that the spider's gut microbiome undergoes pronounced temporal fluctuations, that its assembly is dictated by the consumed prey, and that different prey taxa may remodel the microbiota in drastically different ways.

Response of the bacterial community of Propylea japonica (Thunberg) to Cry2Ab protein

Propylea japonica is a very important predator in agricultural ecosystems, which could be exposed to Bt protein. In this study, the bacterial community of P. japonica fed with normal food and food containing Cry2Ab protein was characterized for the first time using qPCR and high-throughput sequencing approaches. Results showed no effect of Cry2Ab on P. japonica development and reproduction. The most abundant bacterial phylum was Firmicutes, and the most abundant genus was Staphylococcus. The total bacteria copy number was not significantly different across four larval stages. Bacteria species composition was gathered more closely in feed on sucrose solution (sucrose-fed) than in larvae only fed on pea aphid (aphid-fed), the diversity indices of some operational taxonomic unit (OTU) were significantly different between sucrose-fed and aphid-fed samples. Different instar larval stages of P. japonica fed with sucrose solution containing Cry2Ab Bt protein and found no effect on microbial community composition and total bacteria copy numbers. However, effects on relative abundance of microbes, copy numbers of Corynebacterium 1 and Glutamicibacter arilaitensis were observed significantly lower in Bt-fed first and fourth larval stages. Low and high concentrations of Cry2Ab protein altered the microbial abundance relative to sucrose-fed P. japonica and copy numbers of G. arilaitensis and Staphylococcus xylosus were significantly lower in Bt-fed samples than control sucrose-fed. Our results are the first report showing that feeding on Cry2Ab protein does not alter microbial species composition in P. japonica, but effects gene copy number of some dominant bacteria. Further investigations are needed to assess the effect of copy number change on P. japonica.

Entomophagy: Nutritional, ecological, safety and legislation aspects

Globally, there is a need to seek alternative sources of protein in addition to meat. This has led to considerable interest in edible insects. Such insects form part of cultures and diets in many Asian and African countries, and are an excellent source of essential nutrients, minerals, vitamins and proteins. Furthermore, they have been reported to be sustainable. The ecological importance of insects is related to their short life cycles when reared and farmed. This makes them ideal in mitigating greenhouse gas emissions, cutting land uses and polluted water, and reducing environmental contamination. However, the use of edible insects as food in Europe is minimal. To ensure safety of insects when eaten as food, considerations should be made on: microbiological contamination; toxicological hazards, e.g. chemical hazards and antinutrients; allergenicity issues that are related to different exposures, including injection, ingestion, inhalation and skin contact. In this review, we summarize the nutritional and sustainable values of edible insects, look at safety and legislative measures and we finally discuss future issues.

Protein and carbohydrate intakes alter gut microbial community structure in crickets: a Geometric Framework approach

Proteins and carbohydrates have profound impacts on the ecology of gut microbiota, but disentangling the single and interactive effects of different dietary constituents is challenging. Here, we used a multidimensional approach, the Geometric Framework, to study the interactions between nutrition and bacterial abundances with respect to protein and carbohydrate intakes in field cricket, Teleogryllus oceanicus. Our study revealed that species richness decreased as crickets consumed more macronutrients, and species evenness peaked at high intake of protein-rich diets. Sex and protein:carbohydrate (P:C) ratios in diets were the primary factors influencing the gut bacterial community, but most of the microbial operational taxonomic units (OTUs) that were significantly different between males and females were present in low abundance. In contrast, protein intake had a greater influence than carbohydrate consumption on the relative abundances of the core bacterial taxa, as an increase in dietary protein availability could remove the growth constraint imposed by limited nitrogen. Taken together, the use of the Geometric Framework provides a deeper insight into how nutritional intakes influence the relative abundances of gut microbes, and could be a useful tool to integrate the study of gut microbiome and fitness traits in a host.

Bilberry anthocyanin extract promotes intestinal barrier function and inhibits digestive enzyme activity by regulating the gut microbiota in aging rats

This study was aimed at understanding potential mechanisms regarding bilberry anthocyanin extract consumption and healthy aging and the effects on intestinal barrier function and digestive enzyme activity, through regulating the gut microbiota in aging rats. Medium-dose bilberry anthocyanin extract consumption (20 mg per kg bw per day) was the optimum amount to regulate the intestinal function of aging rats. After consumption, bacteria beneficial to the intestine (Aspergillus oryzae, Lactobacillus, Bacteroides, Clostridiaceae-1, the Bacteroidales-S24-7-group and the Lachnospiraceae_NK4A136_group) were induced to grow, and harmful bacteria (Verrucomicrobia and Euryarchaeota) were inhibited. However, high-dose bilberry anthocyanin extract consumption altered some intestinally beneficial bacteria in an adverse way. There was a correlation between changes in bacterial composition and changes in short-chain fatty acids and the intestinal mucosal barrier. Bilberry anthocyanin extract consumption also decreased the activity of digestive enzymes. Our results suggest that bilberry anthocyanin extract consumption is a potential approach for assisting healthy aging.