Most associations between animals and their gut microbiota are dynamic, involving sustained transfer of food-associated microbial cells into the gut and shedding of microorganisms into the external environment with feces, but the interacting effects of host and microbial factors on the composition of the internal and external microbial communities are poorly understood. This study on laboratory cultures of the fruit fly Drosophila melanogaster reared in continuous contact with their food revealed timedependent changes of the microbial communities in the food that were strongly influenced by the presence and abundance of Drosophila. When germfree Drosophila eggs were aseptically added to nonsterile food, the microbiota in the food and flies converged to a composition dramatically different from that in fly-free food, showing that Drosophila has microbiota-independent effects on the food microbiota. The microbiota in both the flies that developed from unmanipulated eggs (bearing microorganisms) and the associated food was dominated by the bacteria most abundant on the eggs, demonstrating effective vertical transmission via surface contamination of eggs. Food coinoculated with a four-species defined bacterial community of Acetobacter and Lactobacillus species revealed the progressive elimination of Lactobacillus from the food bearing few or no Drosophila, indicating the presence of antagonistic interactions between Acetobacter and Lactobacillus. Drosophila at high densities ameliorated the Acetobacter/Lactobacillus antagonism, enabling Lactobacillus to persist. This study with Drosophila demonstrates how animals can have major, coordinated effects on the composition of microbial communities in the gut and immediate environment. F rom a microbiological perspective, an animal is a transient, nutrient-rich patch. The capacity of various microorganisms to exploit the animal habitat involves multiple traits, including mechanisms that evade or modulate the animal immune system (1-3) and metabolic adaptations to utilize host resources (4, 5). Animal-associated microorganisms include pathogens, whose fitness is coupled to host disease and debility, and beneficial forms that variously contribute nutrients, confer protection, and deliver effectors that promote host performance (6). Consequently, the composition of animal-associated microorganisms is an important determinant of animal fitness.Many animal-microbe associations are open systems, meaning that external microorganisms have access to the host habitat and members of the host microbiota are released back to the external environment via feces, sloughed skin, fluid secretions, etc. (7). Open symbioses can be invaded by external microorganisms that are compatible with the host and are competitive with resident microbiota. As a result, the host is potentially more exposed to parasites and cheats than in a closed system but also has an enhanced capacity to modify the composition of its microbiota adaptively to changes in environmental circumstances (8, 9). The shedding of ...

34The hepatitis B virus (HBV) is one of the most widespread human pathogens known today, 35 yet its origin and evolutionary history are still unclear and controversial. Here, we report the 36 analysis of three ancient HBV genomes recovered from human skeletons found at three 37 different archaeological sites in Germany. We reconstructed two Neolithic and one medieval 38 HBV genomes by de novo assembly from shotgun DNA sequencing data. Additionally, we 39 observed HBV-specific peptides using paleo-proteomics. Our results show that HBV 40 circulates in the European population for at least 7000 years. The Neolithic HBV genomes 41show a high genomic similarity to each other. In a phylogenetic network, they do not group 42 with any human-associated HBV genome and are most closely related to those infecting 43African non-human primates. These ancient virus forms appear to represent distinct lineages 44 that have no close relatives today and went possibly extinct. Our results reveal the great 45 potential of ancient DNA from human skeletons in order to study the long-time evolution of 46 blood borne viruses. 47 48 49

Most of the evidence that the gut microbiome of animals is functionally variable, with consequences for the health and fitness of the animal host, is based on laboratory studies, often using inbred animals under tightly controlled conditions. It is largely unknown whether these microbiome effects would be evident in outbred animal populations under natural conditions. In this study, we quantified the functional traits of the gut microbiota (metagenome) and host (gut transcriptome) and the taxonomic composition of the gut microorganisms (16S rRNA gene sequence) in natural populations of three mycophagous Drosophila species. Variation in microbiome function and composition was driven principally by the period of sample collection, while host function varied mostly with Drosophila species, indicating that variation in microbiome traits is determined largely by environmental factors, and not host taxonomy. Despite this, significant correlations between microbiome and host functional traits were obtained. In particular, microbiome functions dominated by metabolism were positively associated with host functions relating to gut epithelial turnover. Much of the functional variation in the microbiome could be attributed to variation in abundance of Bacteroidetes, rather than the two other abundant groups, the γ-Proteobacteria or Lactobacillales. We conclude that functional variation in the interactions between animals and their gut microbiome can be detectable in natural populations, and, in mycophagous Drosophila, this variation relates primarily to metabolism and homeostasis of the gut epithelium.

Despite evidence from laboratory experiments that perturbation of the gut microbiota affects many traits of the animal host, our understanding of the effect of variation in microbiota composition on animals in natural populations is very limited. The core purpose of this study on the fruit fly Drosophila melanogaster was to identify the impact of natural variation in the taxonomic composition of gut bacterial communities on host traits, with the gut transcriptome as a molecular index of microbiota-responsive host traits. Use of the gut transcriptome was validated by demonstrating significant transcriptional differences between the guts of laboratory flies colonized with bacteria and maintained under axenic conditions. Wild Drosophila from six field collections made over two years had gut bacterial communities of diverse composition, dominated to varying extents by Acetobacteraceae and Enterobacteriaceae. The gut transcriptomes also varied among collections and differed markedly from those of laboratory flies. However, no overall relationship between variation in the wild fly transcriptome and taxonomic composition of the gut microbiota was evident at all taxonomic scales of bacteria tested for both individual fly genes and functional categories in Gene Ontology. We conclude that the interaction between microbiota composition and host functional traits may be confounded by uncontrolled variation in both ecological circumstance and host traits (e.g., genotype, age physiological condition) under natural conditions, and that microbiota effects on host traits identified in the laboratory should, therefore, be extrapolated to field population with great caution.

No abstract