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Science no fair!
When Logan Applebaum's mother invents a robotic cousin for him, Logan thinks this may give him an edge in the third grade science fair but the Silverspoon twins have other ideas.
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Antibiotic exposure perturbs the gut microbiota and elevates mortality in honeybees
Gut microbiomes play crucial roles in animal health, and shifts in the gut microbial community structure can have detrimental impacts on hosts. Studies with vertebrate models and human subjects suggest that antibiotic treatments greatly perturb the native gut community, thereby facilitating proliferation of pathogens. In fact, persistent infections following antibiotic treatment are a major medical issue. In apiculture, antibiotics are frequently used to prevent bacterial infections of larval bees, but the impact of antibiotic-induced dysbiosis (microbial imbalance) on bee health and susceptibility to disease has not been fully elucidated. Here, we evaluated the effects of antibiotic exposure on the size and composition of honeybee gut communities. We monitored the survivorship of bees following antibiotic treatment in order to determine if dysbiosis of the gut microbiome impacts honeybee health, and we performed experiments to determine whether antibiotic exposure increases susceptibility to infection by opportunistic pathogens. Our results show that antibiotic treatment can have persistent effects on both the size and composition of the honeybee gut microbiome. Antibiotic exposure resulted in decreased survivorship, both in the hive and in laboratory experiments in which bees were exposed to opportunistic bacterial pathogens. Together, these results suggest that dysbiosis resulting from antibiotic exposure affects bee health, in part due to increased susceptibility to ubiquitous opportunistic pathogens. Not only do our results highlight the importance of the gut microbiome in honeybee health, but they also provide insights into how antibiotic treatment affects microbial communities and host health.
Journal Article
Evolutionary and Ecological Consequences of Gut Microbial Communities
Animals are distinguished by having guts-organs that must extract nutrients from food yet also bar invasion by pathogens. Most guts are colonized by nonpathogenic microorganisms, but the functions of these microbes, or even the reasons why they occur in the gut, vary widely among animals. Sometimes these microorganisms have codiversified with hosts; sometimes they live mostly elsewhere in the environment. Either way, gut microorganisms often benefit hosts. Benefits may reflect evolutionary addiction, whereby hosts incorporate gut microorganisms into normal developmental processes. But benefits often include novel ecological capabilities; for example, many metazoan clades exist by virtue of gut communities enabling new dietary niches. Animals vary immensely in their dependence on gut microorganisms, from lacking them entirely to using them as food or to obligate dependence for development, nutrition, or protection. Many consequences of gut microorganisms for hosts can be ascribed to microbial community processes and the host's ability to shape these processes.
Journal Article
The Hologenome Concept: Helpful or Hollow?
With the increasing appreciation for the crucial roles that microbial symbionts play in the development and fitness of plant and animal hosts, there has been a recent push to interpret evolution through the lens of the \"hologenome\"--the collective genomic content of a host and its microbiome. But how symbionts evolve and, particularly, whether they undergo natural selection to benefit hosts are complex issues that are associated with several misconceptions about evolutionary processes in host-associated microbial communities. Microorganisms can have intimate, ancient, and/or mutualistic associations with hosts without having undergone natural selection to benefit hosts. Likewise, observing host-specific microbial community composition or greater community similarity among more closely related hosts does not imply that symbionts have coevolved with hosts, let alone that they have evolved for the benefit of the host. Although selection at the level of the symbiotic community, or hologenome, occurs in some cases, it should not be accepted as the null hypothesis for explaining features of host-symbiont associations.
Journal Article
Genetic innovations in animal–microbe symbioses
Animal hosts have initiated myriad symbiotic associations with microorganisms and often have maintained these symbioses for millions of years, spanning drastic changes in ecological conditions and lifestyles. The establishment and persistence of these relationships require genetic innovations on the parts of both symbionts and hosts. The nature of symbiont innovations depends on their genetic population structure, categorized here as open, closed or mixed. These categories reflect modes of inter-host transmission that result in distinct genomic features, or genomic syndromes, in symbionts. Although less studied, hosts also innovate in order to preserve and control symbiotic partnerships. New capabilities to sequence host-associated microbial communities and to experimentally manipulate both hosts and symbionts are providing unprecedented insights into how genetic innovations arise under different symbiont population structures and how these innovations function to support symbiotic relationships.The evolutionary persistence of animal symbioses depends on both host and symbiont innovations. Perreau and Moran review how genome sequencing and related experiments have clarified how these innovations arise under different symbiont population structures, categorized here as open, closed and mixed.
Journal Article
Glyphosate perturbs the gut microbiota of honey bees
Glyphosate, the primary herbicide used globally for weed control, targets the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) enzyme in the shikimate pathway found in plants and some microorganisms. Thus, glyphosate may affect bacterial symbionts of animals living near agricultural sites, including pollinators such as bees. The honey bee gut microbiota is dominated by eight bacterial species that promote weight gain and reduce pathogen susceptibility. The gene encoding EPSPS is present in almost all sequenced genomes of bee gut bacteria, indicating that they are potentially susceptible to glyphosate. We demonstrated that the relative and absolute abundances of dominant gut microbiota species are decreased in bees exposed to glyphosate at concentrations documented in the environment. Glyphosate exposure of young workers increased mortality of bees subsequently exposed to the opportunistic pathogen Serratia marcescens. Members of the bee gut microbiota varied in susceptibility to glyphosate, largely corresponding to whether they possessed an EPSPS of class I (sensitive to glyphosate) or class II (insensitive to glyphosate). This basis for differences in sensitivity was confirmed using in vitro experiments in which the EPSPS gene from bee gut bacteria was cloned into Escherichia coli. All strains of the core bee gut species, Snodgrassella alvi, encode a sensitive class I EPSPS, and reduction in S. alvi levels was a consistent experimental result. However, some S. alvi strains appear to possess an alternative mechanism of glyphosate resistance. Thus, exposure of bees to glyphosate can perturb their beneficial gut microbiota, potentially affecting bee health and their effectiveness as pollinators.
Journal Article
Heritable symbiosis: The advantages and perils of an evolutionary rabbit hole
Many eukaryotes have obligate associations with microorganisms that are transmitted directly between generations. A model for heritable symbiosis is the association of aphids, a clade of sap-feeding insects, and Buchnera aphidicola , a gammaproteobacterium that colonized an aphid ancestor 150 million years ago and persists in almost all 5,000 aphid species. Symbiont acquisition enables evolutionary and ecological expansion; aphids are one of many insect groups that would not exist without heritable symbiosis. Receiving less attention are potential negative ramifications of symbiotic alliances. In the short run, symbionts impose metabolic costs. Over evolutionary time, hosts evolve dependence beyond the original benefits of the symbiosis. Symbiotic partners enter into an evolutionary spiral that leads to irreversible codependence and associated risks. Host adaptations to symbiosis (e.g., immune-system modification) may impose vulnerabilities. Symbiont genomes also continuously accumulate deleterious mutations, limiting their beneficial contributions and environmental tolerance. Finally, the fitness interests of obligate heritable symbionts are distinct from those of their hosts, leading to selfish tendencies. Thus, genes underlying the hostâsymbiont interface are predicted to follow a coevolutionary arms race, as observed for genes governing hostâpathogen interactions. On the macroevolutionary scale, the rapid evolution of interacting symbiont and host genes is predicted to accelerate host speciation rates by generating genetic incompatibilities. However, degeneration of symbiont genomes may ultimately limit the ecological range of host species, potentially increasing extinction risk. Recent results for the aphidâ Buchnera symbiosis and related systems illustrate that, whereas heritable symbiosis can expand ecological range and spur diversification, it also presents potential perils.
Journal Article
Gut microbial communities of social bees
Key Points
A distinctive microbial community of approximately nine bacterial species clusters inhabits the bee gut.
These bacteria are host-adapted, and each species cluster occupies particular niches and spatial locations in the bee.
The gut microbial community of the bee is transmitted through social contact, similar to the mode of transmission in mammals.
The characteristic microbial community of the bee gut can be perturbed and invaded by opportunistic microorganisms, which resembles disease states in humans.
There is substantial strain-level diversity in the bee gut microbiota, with individual strains harbouring unique sets of genes with distinct functional capabilities. How this diversity arises and is maintained is not well understood.
Metabolically, most members of the microbial community in the bee gut are fermentative, breaking down the carbohydrate-rich diet of bees into products, such as lactic acid and acetate. Although not yet well-established, these fermentative microorganisms may have a role in contributing to the nutrition of hosts.
The normal bee gut microbiota has been associated with lower levels of infection with pathogens, which may indicate a beneficial role of the microbiota for the host bee.
The bee gut microbiota can be cultured
in vitro
, and gnotobiotic bees can be easily produced, which makes bees a tractable model for the study of the symbiosis of gut microorganisms.
The gut of honey bees is inhabited by a small group of highly host-adapted bacteria. In this Review, Kwong and Moran detail the composition and functions of the microbiota of honey bees and highlight similarities and differences to the human microbiota.
The gut microbiota can have profound effects on hosts, but the study of these relationships in humans is challenging. The specialized gut microbial community of honey bees is similar to the mammalian microbiota, as both are mostly composed of host-adapted, facultatively anaerobic and microaerophilic bacteria. However, the microbial community of the bee gut is far simpler than the mammalian microbiota, being dominated by only nine bacterial species clusters that are specific to bees and that are transmitted through social interactions between individuals. Recent developments, which include the discovery of extensive strain-level variation, evidence of protective and nutritional functions, and reports of eco-physiological or disease-associated perturbations to the microbial community, have drawn attention to the role of the microbiota in bee health and its potential as a model for studying the ecology and evolution of gut symbionts.
Journal Article
Links between metamorphosis and symbiosis in holometabolous insects
Many animals depend on microbial symbionts to provide nutrition, defence or other services. Holometabolous insects, as well as other animals that undergo metamorphosis, face unique constraints on symbiont maintenance. Microbes present in larvae encounter a radical transformation of their habitat and may also need to withstand chemical and immunological challenges. Metamorphosis also provides an opportunity, in that symbiotic associations can be decoupled over development. For example, some holometabolous insects maintain the same symbiont as larvae and adults, but house it in different tissues; in other species, larvae and adults may harbour entirely different types or numbers of microbes, in accordance with shifts in host diet or habitat. Such flexibility may provide an advantage over hemimetabolous insects, in which selection on adult-stage microbial associations may be constrained by its negative effects on immature stages, and vice versa. Additionally, metamorphosis itself can be directly influenced by symbionts. Across disparate insect taxa, microbes protect hosts from pathogen infection, supply nutrients essential for rebuilding the adult body and provide cues regulating pupation. However, microbial associations remain completely unstudied for many families and even orders of Holometabola, and future research will undoubtedly reveal more links between metamorphosis and microbiota, two widespread features of animal life.
This article is part of the theme issue ‘The evolution of complete metamorphosis’.
Journal Article
Hidden Diversity in Honey Bee Gut Symbionts Detected by Single-Cell Genomics
Microbial communities in animal guts are composed of diverse, specialized bacterial species, but little is known about how gut bacteria diversify to produce genetically and ecologically distinct entities. The gut microbiota of the honey bee, Apis mellifera, presents a useful model, because it consists of a small number of characteristic bacterial species, each showing signs of diversification. Here, we used single-cell genomics to study the variation within two species of the bee gut microbiota: Gilliamella apicola and Snodgrassella alvi. For both species, our analyses revealed extensive variation in intraspecific divergence of protein-coding genes but uniformly high levels of 16S rRNA similarity. In both species, the divergence of 16S rRNA loci appears to have been curtailed by frequent recombination within populations, while other genomic regions have continuously diverged. Furthermore, gene repertoires differ markedly among strains in both species, implying distinct metabolic capabilities. Our results show that, despite minimal divergence at 16S rRNA genes, in situ diversification occurs within gut communities and generates bacterial lineages with distinct ecological niches. Therefore, important dimensions of microbial diversity are not evident from analyses of 16S rRNA, and single cell genomics has potential to elucidate processes of bacterial diversification.
Journal Article