Cultivation-independent characterization of 'Candidatus Magnetobacterium bavaricum' via ultrastructural, geochemical, ecological and metagenomic methods.

'Candidatus Magnetobacterium bavaricum' is unusual among magnetotactic bacteria (MTB) in terms of cell size (8-10 µm long, 1.5-2 µm in diameter), cell architecture, magnetotactic behaviour and its distinct phylogenetic position in the deep-branching Nitrospira phylum. In the present study, improved magnetic enrichment techniques permitted high-resolution scanning electron microscopy and energy dispersive X-ray analysis, which revealed the intracellular organization of the magnetosome chains. Sulfur globule accumulation in the cytoplasm point towards a sulfur-oxidizing metabolism of 'Candidatus M. bavaricum'. Detailed analysis of 'Candidatus M. bavaricum' microhabitats revealed more complex distribution patterns than previously reported, with cells predominantly found in low oxygen concentration. No correlation to other geochemical parameters could be observed. In addition, the analysis of a metagenomic fosmid library revealed a 34 kb genomic fragment, which contains 33 genes, among them the complete rRNA gene operon of 'Candidatus M. bavaricum' as well as a gene encoding a putative type IV RubisCO large subunit.