Microprofiles of oxygen, redox potential, and pH, and microbial fermentation products in the highly alkaline gut of the saprophagous larva of Penthetria holosericea (Diptera: Bibionidae)

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.

Crosstalk between the microbiota and insect postembryonic development

Insect sequential development evolves from a simple molt towards complete metamorphosis. Like any multicellular host, insects interact with a complex microbiota. In this review, factors driving the microbiota dynamics were pointed out along their development. Special focus was put on tissue renewal, shift in insect ecology, and microbial interactions. Conversely, how the microbiota modulates its host development through nutrient acquisition, hormonal control, and cellular or tissue differentiation was exemplified. Such modifications might have long-term carry-over effects on insect physiology. Finally, remarkable microbe-driven control of insect behaviors along their life cycle was highlighted. Increasing knowledge of those interactions might offer new insights on how insects respond to their environment as well as perspectives on pest- or vector-control strategies.

Destabilization of the Bacterial Interactome Identifies Nutrient Restriction-Induced Dysbiosis in Insect Guts

Stress-associated dysbiosis of microbiome can have several configurations that, under an energy landscape conceptual framework, can change from one configuration to another due to different alternating selective forces. It has been proposed-according to the Anna Karenina Principle-that in stressed individuals the microbiome are more dispersed (i.e., with a higher within-beta diversity), evidencing the grade of dispersion as indicator of microbiome dysbiosis. We hypothesize that although dysbiosis leads to different microbial communities in terms of beta diversity, these are not necessarily differently dispersed (within-beta diversity), but they form disrupted networks that make them less resilient to stress. To test our hypothesis, we select nutrient restriction (NR) stress that impairs host fitness but does not introduce overt microbiome selectors, such as toxic compounds and pathogens. We fed the polyphagous black soldier fly, Hermetia illucens, with two NR diets and a control full-nutrient (FN) diet. NR diets were dysbiotic because they strongly affected insect growth and development, inducing significant microscale changes in physiochemical conditions of the gut compartments. NR diets established new configurations of the gut microbiome compared to FN-fed guts but with similar dispersion. However, these new configurations driven by the deterministic changes induced by NR diets were reflected in rarefied, less structured, and less connected bacterial interactomes. These results suggested that while the dispersion cannot be considered a consistent indicator of the unhealthy state of dysbiotic microbiomes, the capacity of the community members to maintain network connections and stability can be an indicator of the microbial dysbiotic conditions and their incapacity to sustain the holobiont resilience and host homeostasis. IMPORTANCE Changes in diet play a role in reshaping the gut microbiome in animals, inducing dysbiotic configurations of the associated microbiome. Although studies have reported on the effects of specific nutrient contents on the diet, studies regarding the conditions altering the microbiome configurations and networking in response to diet changes are limited. Our results showed that nutrient poor diets determine dysbiotic states of the host with reduction of insect weight and size, and increase of the times for developmental stage. Moreover, the poor nutrient diets lead to changes in the compositional diversity and network interaction properties of the gut microbial communities. Our study adds a new component to the understanding of the ecological processes associated with dysbiosis, by disentangling consequences of diets on microbiome dysbiosis that is manifested with the disruption of microbiome networking properties rather than changes in microbiome dispersion and beta diversity.

Hot and sour: parasite adaptations to honeybee body temperature and pH

Host temperature and gut chemistry can shape resistance to parasite infection. Heat and acidity can limit trypanosomatid infection in warm-blooded hosts and could shape infection resistance in insects as well. The colony-level endothermy and acidic guts of social bees provide unique opportunities to study how temperature and acidity shape insect-parasite associations. We compared temperature and pH tolerance between three trypanosomatid parasites from social bees and a related trypanosomatid from poikilothermic mosquitoes, which have alkaline guts. Relative to the mosquito parasites, all three bee parasites had higher heat tolerance that reflected body temperatures of hosts. Heat tolerance of the honeybee parasite Crithidia mellificae was exceptional for its genus, implicating honeybee endothermy as a plausible filter of parasite establishment. The lesser heat tolerance of the emerging Lotmaria passim suggests possible spillover from a less endothermic host. Whereas both honeybee parasites tolerated the acidic pH found in bee intestines, mosquito parasites tolerated the alkaline conditions found in mosquito midguts, suggesting that both gut pH and temperature could structure host-parasite specificity. Elucidating how host temperature and gut pH affect infection-and corresponding parasite adaptations to these factors-could help explain trypanosomatids' distribution among insects and invasion of mammals.

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

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

Compartmentalization of bacterial and fungal microbiomes in the gut of adult honeybees

The core gut microbiome of adult honeybee comprises a set of recurring bacterial phylotypes, accompanied by lineage-specific, variable, and less abundant environmental bacterial phylotypes. Several mutual interactions and functional services to the host, including the support provided for growth, hormonal signaling, and behavior, are attributed to the core and lineage-specific taxa. By contrast, the diversity and distribution of the minor environmental phylotypes and fungal members in the gut remain overlooked. In the present study, we hypothesized that the microbial components of forager honeybees (i.e., core bacteria, minor environmental phylotypes, and fungal members) are compartmentalized along the gut portions. The diversity and distribution of such three microbial components were investigated in the context of the physico-chemical conditions of different gut compartments. We observed that changes in the distribution and abundance of microbial components in the gut are consistently compartment-specific for all the three microbial components, indicating that the ecological and physiological interactions among the host and microbiome vary with changing physico-chemical and metabolic conditions of the gut.

Taking Different Roads: l-Tryptophan as the Origin of Psilocybe Natural Products

Psychotropic fungi of the genus Psilocybe, colloquially referred to as "magic mushrooms", are best known for their l-tryptophan-derived major natural product, psilocybin. Yet, recent research has revealed a more diverse secondary metabolism that originates from this amino acid. In this minireview, the focus is laid on l-tryptophan and the various Psilocybe natural products and their metabolic routes are highlighted. Psilocybin and its congeners, the heterogeneous blue-colored psilocyl oligomers, alongside β-carbolines and N,N-dimethyl-l-tryptophan, are presented as well as current knowledge on their biosynthesis is provided. The multidisciplinary character of natural product research is demonstrated, and pharmacological, medicinal, ecological, biochemical, and evolutionary aspects are included.

Evolutionary trends of digestion and absorption in the major insect orders

The spatial organization of digestion, which corresponds to the steps by which the ingested food is hydrolyzed in the different regions of the gut, was described in insects from the major insect orders. The pattern of digestion and absorption in the midgut shows a strong phylogenetic influence, modulated by adaptation to particular feeding habits. Based on this, basic digestive patterns were recognized and were proposed to represent the major ancestors from which the different orders evolved. The putative ancestors chosen to represent different points in the evolution from basal Neoptera to more derived orders were: Neoptera, Polyneoptera, Hemiptera, Hymenoptera-Panorpoidea (Diptera-Lepidoptera), Lepidoptera, and Cyclorrhapha. The basic plan of Neoptera was supposed to be alike that of Polyneoptera, which was hypothesized from studies performed in grasshoppers, crickets and from stick insects. For Holometabola, the basic plan was initially proposed from studies carried out in beetles, bees, nematocerous flies, common flies and also from moths. This review updates the physiological data supporting the putative midgut basic patterns by discussing available data on insects pertaining to different taxa and details the evolutionary trends of midgut function among the major insect orders. Furthermore, by using recent genomic and transcriptome data, this review discusses the few insects for which the spatial organization of midgut absorption is known.

Developmental stages and gut microenvironments influence gut microbiota dynamics in the invasive beetle Popillia japonica Newman (Coleoptera: Scarabaeidae)

Popillia japonica Newman (Coleoptera: Scarabaeidae) is a highly polyphagous invasive beetle originating from Japan. This insect is highly resilient and able to rapidly adapt to new vegetation. Insect-associated microorganisms can play important roles in insect physiology, helping their hosts to adapt to changing conditions and potentially contributing to an insect's invasive potential. Such symbiotic bacteria can be part of a core microbiota that is stably transmitted throughout the host's life cycle or selectively recruited from the environment at each developmental stage. The aim of this study was to investigate the origin, stability and turnover of the bacterial communities associated with an invasive population of P. japonica from Italy. Our results demonstrate that soil microbes represent an important source of gut bacteria for P. japonica larvae, but as the insect develops, its gut microbiota richness and diversity decreased substantially, paralleled by changes in community composition. Notably, only 16.75% of the soil bacteria present in larvae are maintained until the adult stage. We further identified the micro-environments of different gut sections as an important factor shaping microbiota composition in this species, likely due to differences in pH, oxygen availability and redox potential. In addition, P. japonica also harboured a stable bacterial community across all developmental stages, consisting of taxa well known for the degradation of plant material, namely the families Ruminococcacae, Christensenellaceae and Lachnospiraceae. Interestingly, the family Christensenallaceae had so far been observed exclusively in humans. However, the Christensenellaceae operational taxonomic units found in P. japonica belong to different taxonomic clades within this family.

Symbiosis in Sustainable Agriculture: Can Olive Fruit Fly Bacterial Microbiome Be Useful in Pest Management?

The applied importance of symbiosis has been gaining recognition. The relevance of symbiosis has been increasing in agriculture, in developing sustainable practices, including pest management. Insect symbiotic microorganisms' taxonomical and functional diversity is high, and so is the potential of manipulation of these microbial partners in suppressing pest populations. These strategies, which rely on functional organisms inhabiting the insect, are intrinsically less susceptible to external environmental variations and hence likely to overcome some of the challenges posed by climate change. Rates of climate change in the Mediterranean Basin are expected to exceed global trends for most variables, and this warming will also affect olive production and impact the interactions of olives and their main pest, the obligate olive fruit fly (Bactrocera oleae). This work summarizes the current knowledge on olive fly symbiotic bacteria towards the potential development of symbiosis-based strategies for olive fruit fly control. Particular emphasis is given to Candidatus Erwinia dacicola, an obligate, vertically transmitted endosymbiont that allows the insect to cope with the olive-plant produced defensive compound oleuropein, as a most promising target for a symbiosis disruption approach.

Not all animals need a microbiome

It is often taken for granted that all animals host and depend upon a microbiome, yet this has only been shown for a small proportion of species. We propose that animals span a continuum of reliance on microbial symbionts. At one end are the famously symbiont-dependent species such as aphids, humans, corals and cows, in which microbes are abundant and important to host fitness. In the middle are species that may tolerate some microbial colonization but are only minimally or facultatively dependent. At the other end are species that lack beneficial symbionts altogether. While their existence may seem improbable, animals are capable of limiting microbial growth in and on their bodies, and a microbially independent lifestyle may be favored by selection under some circumstances. There is already evidence for several ‘microbiome-free’ lineages that represent distantly related branches in the animal phylogeny. We discuss why these animals have received such little attention, highlighting the potential for contaminants, transients, and parasites to masquerade as beneficial symbionts. We also suggest ways to explore microbiomes that address the limitations of DNA sequencing. We call for further research on microbiome-free taxa to provide a more complete understanding of the ecology and evolution of macrobe-microbe interactions.

No evidence that gut microbiota impose a net cost on their butterfly host

Gut microbes are believed to play a critical role in most animal life, yet fitness effects and cost–benefit trade‐offs incurred by the host are poorly understood. Unlike most hosts studied to date, butterflies largely acquire their nutrients from larval feeding, leaving relatively little opportunity for nutritive contributions by the adult's microbiota. This provides an opportunity to measure whether hosting gut microbiota comes at a net nutritional price. Because host and bacteria may compete for sugars, we hypothesized that gut flora would be nutritionally neutral to adult butterflies with plentiful food, but detrimental to semistarved hosts, especially when at high density. We held field‐caught adult Speyeria mormonia under abundant or restricted food conditions. Because antibiotic treatments did not generate consistent variation in their gut microbiota, we used interindividual variability in bacterial loads and operational taxonomic unit abundances to examine correlations between host fitness and the abdominal microbiota present upon natural death. We detected strikingly few relationships between microbial flora and host fitness. Neither total bacterial load nor the abundances of dominant bacterial taxa were related to butterfly fecundity, egg mass or egg chemical content. Increased abundance of a Commensalibacter species did correlate with longer host life span, while increased abundance of a Rhodococcus species correlated with shorter life span. Contrary to our expectations, these relationships were unchanged by food availability to the host and were unrelated to reproductive output. Our results suggest the butterfly microbiota comprises parasitic, commensal and beneficial taxa that together do not impose a net reproductive cost, even under caloric stress.

Caterpillars lack a resident gut microbiome

Many animals are inhabited by microbial symbionts that influence their hosts' development, physiology, ecological interactions, and evolutionary diversification. However, firm evidence for the existence and functional importance of resident microbiomes in larval Lepidoptera (caterpillars) is lacking, despite the fact that these insects are enormously diverse, major agricultural pests, and dominant herbivores in many ecosystems. Using 16S rRNA gene sequencing and quantitative PCR, we characterized the gut microbiomes of wild leaf-feeding caterpillars in the United States and Costa Rica, representing 124 species from 15 families. Compared with other insects and vertebrates assayed using the same methods, the microbes that we detected in caterpillar guts were unusually low-density and variable among individuals. Furthermore, the abundance and composition of leaf-associated microbes were reflected in the feces of caterpillars consuming the same plants. Thus, microbes ingested with food are present (although possibly dead or dormant) in the caterpillar gut, but host-specific, resident symbionts are largely absent. To test whether transient microbes might still contribute to feeding and development, we conducted an experiment on field-collected caterpillars of the model species Manduca sexta Antibiotic suppression of gut bacterial activity did not significantly affect caterpillar weight gain, development, or survival. The high pH, simple gut structure, and fast transit times that typify caterpillar digestive physiology may prevent microbial colonization. Moreover, host-encoded digestive and detoxification mechanisms likely render microbes unnecessary for caterpillar herbivory. Caterpillars illustrate the potential ecological and evolutionary benefits of independence from symbionts, a lifestyle that may be widespread among animals.

Approaches to studying and manipulating the enteric microbiome to improve autism symptoms

There is a growing body of scientific evidence that the health of the microbiome (the trillions of microbes that inhabit the human host) plays an important role in maintaining the health of the host and that disruptions in the microbiome may play a role in certain disease processes. An increasing number of research studies have provided evidence that the composition of the gut (enteric) microbiome (GM) in at least a subset of individuals with autism spectrum disorder (ASD) deviates from what is usually observed in typically developing individuals. There are several lines of research that suggest that specific changes in the GM could be causative or highly associated with driving core and associated ASD symptoms, pathology, and comorbidities which include gastrointestinal symptoms, although it is also a possibility that these changes, in whole or in part, could be a consequence of underlying pathophysiological features associated with ASD. However, if the GM truly plays a causative role in ASD, then the manipulation of the GM could potentially be leveraged as a therapeutic approach to improve ASD symptoms and/or comorbidities, including gastrointestinal symptoms. One approach to investigating this possibility in greater detail includes a highly controlled clinical trial in which the GM is systematically manipulated to determine its significance in individuals with ASD. To outline the important issues that would be required to design such a study, a group of clinicians, research scientists, and parents of children with ASD participated in an interdisciplinary daylong workshop as an extension of the 1st International Symposium on the Microbiome in Health and Disease with a Special Focus on Autism (www.microbiome-autism.com). The group considered several aspects of designing clinical studies, including clinical trial design, treatments that could potentially be used in a clinical trial, appropriate ASD participants for the clinical trial, behavioral and cognitive assessments, important biomarkers, safety concerns, and ethical considerations. Overall, the group not only felt that this was a promising area of research for the ASD population and a promising avenue for potential treatment but also felt that further basic and translational research was needed to clarify the clinical utility of such treatments and to elucidate possible mechanisms responsible for a clinical response, so that new treatments and approaches may be discovered and/or fostered in the future.