Biodiversity of Magnetotactic Bacteria in the Freshwater Lake Beloe Bordukovskoe, Russia

According to 16S rRNA gene- or genome-based phylogeny, magnetotactic bacteria (MTB) belong to diverse taxonomic groups. Here we analyzed the diversity of MTB in a sample taken from the freshwater Lake Beloe Bordukovskoe near Moscow, Russia, by using molecular identification based on sequencing of the 16S rRNA gene and mamK , a specific marker gene for these bacteria. A protein encoded by the mamK gene is involved in magnetosome chain arrangement inside the cell. As a result, six operational taxonomic units (OTUs) of MTB were identified. Among them, OTUs affiliated with the phylum Nitrospirae were predominant. ‘ Ca . Etaproteobacteria’ and Alphaproteobacteria represented the minor groups of MTB. We also identified a novel MTB belonging to the family Syntrophaceae of the Deltaproteobacteria class. Using a combination of fluorescence and transmission electron microscopy, the bacteria belonging to these new MTB groups were visualized. Electron microscopy revealed that Syntrophaceae MTB were rod-shaped and synthesized elongated magnetosomes, arranged as a disorganized cluster. Among the Nitrospirae group, two groups with vibrioid cell shape and one group of ovoid-shaped bacteria were identified, all of which had elongated magnetosome crystals consisting of magnetite.