Ecogenomics of genome-streamlined freshwater microbes
Presenta: Michaela M. Salcher
Limnological Station, University of Zurich, Switzerland
Freshwater microbes are centrally involved in chemical turnover processes, yet individual microbial populations greatly differ in their metabolic and ecological features. The most abundant microbes in the plankton of lakes are of conspicuously small size (cell volumes <0.1 μm3) and have reduced genomes (<1.5 Mb). Streamlining theory predicts that gene loss is caused by evolutionary selection driven by environmental factors, making these organisms superior competitors for limiting resources under oligotrophic conditions. Although such streamlined microbes numerically dominate in lakes, they are still poorly studied, mainly because of problems establishing axenic cultures. A newly developed isolation strategy allowed us to bring some of these oligotrophs in culture, e.g., members of the most abundant freshwater microbes, the acI Actinobacteria ('Ca. Nanopelagicales') and 'Ca. Methylopumilus planktonicus' (Betaproteobacteria). Whole genome sequencing and comparative population-genomics in combination with high-resolution monitoring identified a high degree of microdiversification in closely related genotypes. This ecotype diversification reflects a possible niche-specific adaptation and might be the reason for the observed high total population numbers in lakes.
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