Diversity and Taxonomy of Magnetotactic Bacteria

Abstract

Studies of the diversity of magnetotactic bacteria (MTB) benefit from the unique advantage that MTB can be readily separated from sediment particles and other bacteria based on their magnetotaxis. This is the reason why current knowledge on MTB diversity relies to a lesser extent on the isolation and characterization of pure cultures, the classical tool of microbiology, than in other groups of microorganisms. Microscopy of magnetotactic enrichments retrieved from various environmental samples has consistently revealed significant morphological and ultrastructural diversity of MTB. However, of the many morphotypes detected, including spirilla, cocci, vibrios, ovoid, rod-shaped and even multicellular bacteria, only few bacteria could so far be brought into pure culture. The taxonomy of MTB is therefore heavily based on comparative sequence analysis of their 16S rRNA genes which can be investigated without prior cultivation. Based on 16S rRNA sequence similarity MTB are polyphyletic. Most of the MTB pure cultures and many of the so far uncultured phylotypes cluster within the Alphaproteobacteria, but MTB have also been affiliated to Deltaproteobacteria, to the phylum Nitrospira, and, tentatively, also to Gammaproteobacteria.