Dominating Role of an Unusual Magnetotactic Bacterium in the Microaerobic Zone of a Freshwater Sediment

Abstract

A combination of polymerase chain reaction-assisted rRNA sequence retrieval and fluorescent oligonucleotide probing was used to identify in situ a hitherto unculturable, big, magnetotactic, rod-shaped organism in freshwater sediment samples collected from Lake Chiemsee. Tentatively named "Magnetobacterium bavaricum," this bacterium is evolutionarily distant from all other phylogenetically characterized magnetotactic bacteria and contains unusually high numbers of magnetosomes (up to 1,000 magnetosomes per cell). The spatial distribution in the sediment was studied, and up to 7 x 10' active cells per cm3 were found in the microaerobic zone. Considering its average volume (25.8 + 4.1 ,um3) and relative abundance (0.64 + 0.17%), "M. bavaricum" may account for approximately 30% of the microbial biovolume and may therefore be a dominant fraction of the microbial community in this layer. Its microhabitat and its high content of sulfur globules and magnetosomes suggest that this organism has an iron-dependent way of energy conservation which depends on balanced gradients of oxygen and sulfide.

Cultivation‐independent characterization of ‘Candidatus Magnetobacterium bavaricum’ via ultrastructural, geochemical, ecological and metagenomic methods

“…Since cultivation attempts failed so far, we applied culture-independent characterization techniques, such as microsensor measurements, metagenomic analysis and MTB mass collection to further characterize 'Candidatus M. bavaricum'. In addition, refined structural analyses of magnetosome organization and sulfur globule content verified the previously hypothesized arrangement of magnetosome chains adjacent to the cell envelope and provides further evidence for a sulfur oxidizing metabolism of 'Candidatus M. bavaricum' (Spring et al, 1993;Hanzlik et al, 1996).…”

Identification of acetate‐utilizing Bacteria and Archaea in methanogenic profundal sediments of Lake Kinneret (Israel) by stable isotope probing of rRNA

“…After 18 days of incubation, the 13 C-labelled bacterial community consisted mainly of members of the Nitrospira phylum, and to a minor extent of members of the Firmicutes and the candidate division 'Endomicrobia'. The Nitrospira phylum contains among others the iron reducer candidatus 'Magnetobacterium bavaricum' (Spring et al, 1993) and the sulfur reducers Thermodesulfovibrio yellowstonii and T. islandicus (Henry et al, 1994;Sonne-Hansen and Ahring, 1999), which, however, showed only about 87-88% sequence similarity to sequences retrieved in this study (Fig. 5).…”

Comparative analysis of magnetosome gene clusters in magnetotactic bacteria provides further evidence for horizontal gene transfer

“…Thus MTB do not form a coherent phylogenetic group. While most of the freshwater MTB like the magnetospirilla and the marine strains MC-1 and MV-1 belong to the Alphaproteobacteria (Williams et al, 2006), magnetotactic representatives are also scattered within the Deltaproteobacteria and the Nitrospira phyla (DeLong et al, 1993;Spring et al, 1993;Sakaguchi et al, 2002), and there are some indications for the presence of greigite-producing MTB within the Gammaproteobacteria (Simmons et al, 2004). Because of this phylogenetic diversity, the origin of magnetotaxis was initially thought to be the result of independent evolutionary processes in distinct phyla (DeLong et al, 1993); however, recent findings suggest this diversity and the wide distribution of the magnetotactic phenotype is a result of horizontal gene transfer (HGT) (Schübbe et al, 2003;Ullrich et al, 2005).…”