Improved technique for the isolation of magnetotactic spirilla from a freshwater sediment and their phylogenetic characterization.

An improved technique for the isolation of magnetotactic bacteria was used for the axenic cultivation of microaerophilic magnetotactic spirilla. Magnetotactic bacteria were first separated from non-magnetic contaminants by exploiting their active migration along magnetic field lines by a capillary "racetrack" method. The purified magnetic cells were then inoculated into a two-layer isolation medium with opposing oxygen and sulfide gradients. Several strains of magnetotactic spirilla were isolated from a freshwater sediment sample using this method. Based on their morphology, physiology and comparative analysis of almost complete 16S rRNA gene sequences, all newly isolated strains were identified as members of the genus Magnetospirillum. While five of the isolates were closely related to previously described species (> 99% sequence similarity), two isolates appear to represent a third phylogenetic cluster within the genus Magnetospirillum.