Common structuring principles of the Drosophila melanogaster microbiome on a continental scale and between host and substrate

Summary The relative importance of host control, environmental effects and stochasticity in the assemblage of host-associated microbiomes is being debated. We analysed the microbiome among fly populations that were sampled across Europe by the European Drosophila Population Genomics Consortium (DrosEU). In order to better understand the structuring principles of the natural D. melanogaster microbiome, we combined environmental data on climate and food-substrate with dense genomic data on host populations and microbiome profiling. Food-substrate, temperature, and host population structure correlated with microbiome structure. Microbes, whose abundance was co-structured with host populations, also differed in abundance between flies and their substrate in an independent survey. This finding suggests common, host-related structuring principles of the microbiome on different spatial scales

Differential ecological specificity of protist and bacterial microbiomes across a set of termite species

The gut microbiome of lower termites comprises protists and bacteria that help these insects to digest cellulose and to thrive on wood. The composition of the termite gut microbiome correlates with phylogenetic distance of the animal host and host ecology (diet) in termites collected from their natural environment. However, carryover of transient microbes from host collection sites are an experimental concern and might contribute to the ecological imprints on the termite gut microbiome. Here, we set out to test whether an ecological imprint on the termite gut microbiome remains, when focusing on the persistent microbiome. Therefore, we kept five termite species under strictly controlled dietary conditions and subsequently profiled their protist and bacterial gut microbial communities using 18S and 16S rRNA gene amplicon sequencing. The species differed in their ecology; while three of the investigated species were wood-dwellers that feed on the piece of wood they live in and never leave except for the mating flight, the other two species were foragers that regularly leave their nests to forage for food. Despite these prominent ecological differences, protist microbiome structure aligned with phylogenetic relatedness of termite host species. Conversely, bacterial communities seemed more flexible, suggesting that microbiome structure aligned more strongly with the foraging and wood-dwelling ecologies. Interestingly, protist and bacterial community alpha-diversity correlated, suggesting either putative interactions between protists and bacteria, or that both types of microbes in the termite gut follow shared structuring principles. Taken together, our results add to the notion that bacterial communities are more variable over evolutionary time than protist communities and might react more flexibly to changes in host ecology. © 2017 Waidele, Korb, Voolstra, Künzel, Dedeine and Staubach

The eukaryome: Diversity and role of microeukaryotic organisms associated with animal hosts

Awareness of the roles that host-associated microbes play in host biology has escalated in recent years. However, microbiome studies have focused essentially on bacteria, and overall, we know little about the role of host-associated eukaryotes outside the field of parasitology. Despite that, eukaryotes and microeukaryotes in particular are known to be common inhabitants of animals. In many cases, and/or for long periods of time, these associations are not associated with clinical signs of disease. Unlike the study of bacterial microbiomes, the study of the microeukaryotes associated with animals has largely been restricted to visual identification or molecular targeting of particular groups. So far, since the publication of the influential Human Microbiome Project Consortium paper in 2012, few studies have been published dealing with the microeukaryotes using a high-throughput barcoding 'microbiome-like' approach in animals. Nonetheless, microeukaryotes have an impact on the host physiology and lifestyle and also on the diversity and composition of the wider symbiotic community of bacteria and viruses. Beyond being parasites, microeukaryotes have many different roles in animals. For example, they directly interact with the host immune system in mammals; they have a key role on cellulose degradation, lignocellulose in xylophage termites and cockroaches; and they have an essential role in providing photosynthates to reef-building corals. Certain microeukaryotic lineages have diversified within hosts more than others. These cases of co-evolution led to different forms of symbiosis: from mutualism (like Symbiodinium in corals or parabasalians in termites), to commensalism (Blastocystis in humans) or to strict parasitism (apicomplexans or microsporidians in a broad range of hosts). We will review the ecological context and the evolutionary mechanisms that ended up in these different symbiotic scenarios, across the taxonomic range of both symbionts and their metazoan hosts. Host-associated microeukaryotes have impacts at many levels, from individual animal health to ecosystems and to agroeconomy. Therefore, it is crucial to have a better understanding of their diversity and roles. Novel methodologies are being developed to access the eukaryotic fraction of the microbiome using high-throughput methods. From -omics, to imaging and barcoding approaches biased against metazoans, these novel methodologies and strategies are helping us to increase and improve our knowledge of microeukaryotes in animal-associated environments. A free Plain Language Summary can be found within the Supporting Information of this article