Niche-directed evolution modulates genome architecture in freshwater Planctomycetes
Large numbers of bacteria live in freshwater lakes and reservoirs. The microbial universe of these ecosystems is largely unexplored due to our current inability to grow these tiny lifeforms under laboratory conditions. A joint research team from the Department of Aquatic Microbial Ecology (Institute of Hydrobiology, BC, CAS) recently discovered new groups of bacteria thriving in aquatic freshwater habitats.
Using samples collected from different location within Europe (Římov Reservoir - Czech Republic; Amadorio Reservoir – Spain; Lake Zurich - Switzerland) and DNA-based methods, they studied the ecology and evolutionary history of new bacterial taxa which received names inspired by Slavic and Germanic folklore. Thus, the study of bacteria from the proposed families of Nemodlikiaceae (named after Nemodliki, tutelary deities of water in Bohemian and Moravian mythology), Vodnikaceae (named after Vodník, mythical Slavic water spirit) and Nixeaceae (named after Nixe, aquatic being in Germanic folklore) revealed cues about microbial specialization, habitat transition and genome evolution in freshwater environments. The work was published in The ISME Journal.
Figure: Spatiotemporal profiles of Planctomycetes relative abundance (horizontal bars), temperature (red line), chlorophyll a (green line) and oxygen (blue line) in Lake Zurich (a) and Rimov Reservoir (b) during 2015. The vertical axis shows the depth (m), within the water column, from which the samples were collected (9 for Lake Zurich and 6 for Rimov Reservoir). The upper X-axis shows the percent of Phycisphaerae (red bars) and Planctomycetacia (dark cyan) within the prokaryotic communities (estimated as the total sum of DAPI-positive cells), while the lower one displays the values for temperature, chlorophyll a and oxygen. The sampling date is shown above the lower X-axis. The panels c, d and e display superimposed images of CARD-FISH-stained Planctomycetes (class Phycisphaerae, family Nemodlikiaceae) and DAPI-stained prokaryotes. The red arrows point towards free-living and particle-associated Planctomycetes, while the yellow ones designate unhybridized prokaryotic cells. The scale bar is 5 µm.
Figure: (a–d) Phylogenomic subtrees for Freshwater Planctomycetes. The black colored branches designate aquatic groups(Vodnikaceae, Nixeaceae, Nemodlikiaceae), while the grey ones their closest relatives (found in soil/sediments). The circular symbols, situated at the tips of the branches, are proportional with genome size and depict gene densities (within genomes). The number of genomes present in the collapsed groups is specified in parenthesis. (e) Putative model of niche-directed genome evolution in freshwater Planctomycetes
For more detailed information, check the publication in the ISME Journal
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Andrei, A.S., Salcher, M. M., Mehrshad, M., Rychtecký, P., Znachor, P. & Ghai, R. 2019. Niche-directed evolution modulates genome architecture in freshwater Planctomycetes. The ISME Journal.