Culture-independent characterization of a novel, uncultivated magnetotactic member of the Nitrospirae phylum

A magnetotactic bacterium, designated strain LO-1, of the Nitrospirae phylum was detected and concentrated from a number of freshwater and slightly brackish aquatic environments in southern Nevada. The closest phylogenetic relative to LO-1 is Candidatus Magnetobacterium bavaricum based on a 91.2% identity in their 16S rRNA gene sequence. Chemical and cell profiles of a microcosm containing water and sediment show that cells of strain LO-1 are confined to the oxic-anoxic interface and the upper regions of the anaerobic zone which in this case, occurred in the sediment. This microorganism is relatively large, ovoid in morphology and usually biomineralizes three braid-like bundles of multiple chains of bullet-shaped magnetosomes that appeared to be enclosed in a magnetosome membrane. Cells of LO-1 had an unusual three-layered unit membrane cell wall and contained several types of inclusions, some of which are sulfur-rich. Strain LO-1 is motile by means of a single bundle of sheathed flagella and exhibits the typical 'wobbling' motility and helical swimming ('flight') path of the magnetotactic cocci. This study and reports from others suggest that LO-1-like organisms are widespread in sediments of freshwater to brackish natural aquatic environments.