Abstract:
Metagenomic sequencing has been developed in recent years as a tool to study biological communities that reside in specific environments by sequencing the genetic content of all community members together. A deep sampling of the genomic space enables the extraction of further information on genetic heterogeneity within the community members that can be used for an evolutionary reconstruction. We show how high-resolution metagenomic data sets can be used for testing evolutionary hypotheses on the impact of selection, genetic drift and geographic structure.
First, an analysis of a microbial symbiont community inhabiting Bathymodiolus mussels is presented. We characterize the symbiont genetic variation across multiple individual mussels.The mode of symbiont transmission may be inferred from the pattern of genetic variation among symbiotic populations, especially from the degree of population differentiation and the presence or absence of host-specific SNPs. Metagenomic data sets from multiple mussels were cross-assembled and binned into bacterial species. We find one highly abundant and one less abundant symbiont. Single-nucleotide polymorphisms (SNPs) are analysed to quantify the genetic variation and population structure of the abundant species. We find that host-specific SNPs are rather rare but population structure is present among the samples. We hypothesize that the observed pattern is caused either by geographic isolation or by selection during symbiont uptake into the host and symbiont maintenance over time.
In a second analysis we aim to quantify the impact of selection and drift on microevolution in phages. Therefore a time-series metagenomics data set is utilized to estimate SNP frequencies over time. The directed change of SNP frequencies with time is used as an estimate for positive selection. This pattern is only present in one of the two highly abundant phages analysed. In this phage, the impact of selection is varying between genes indicating the presence of strong genetic linkage in the selected region and weaker linkage in other regions.
Anne Kupczok - Institute of General Microbiology, Kiel University, Germany
Ort: INB Seminarraum
