Biodiversity and magnetotaxis mechanism of magnetotactic bacteria

Abstract: Using bacteriological, microscopic and physics approaches, we studied the magnetotactic bacteria collected from the Mediterranean Sea. A remarkable diversity of morphotypes was observed, in which multicellular types seemed to differ from those previously found in North and South America. In addition, we have isolated the first axenic magnetotactic bacterial culture from the Mediterranean Sea. The magneto-ovoid strain (MO-1) is a Gram-negative, obligatory microaerophilic ovoid bacterium. MO-1 grows chemolitho-autotrophically with thiosulfate as electron donors and HCO3-/CO2 as the sole carbon source. Each cell contains one chain of average 16 magnetosomes. The magnetosome crystals of MO-1 cells were identified as cubo-octahedral shape magnetite. In addition, each cell contains two phosphor-rich aggregates (globules?) and 1-7 vesicles of unknown nature. Sequence comparison of the 16S rDNA gene has shown that the closest related bacterium is Magnetococcus sp. MC-1 with 93% sequence identity. Therefore, the MO-1 strain might belong to a new genius affiliated with the alpha subclass of Proteobacteria. The genome size of MO-1 has been determined as about 6 Mb by PFGE analysis.We have developed a quantitative method to analyze magnetotaxis behaviour of magnetotactic bacteria. This method allows us to distinct polar from axial magnetotaxis and north-seeking from south-seeking. It also allows to calculate the velocity of magnetotactic motility and to estimate the contribution of passive alignment and active adjustment to the magnetotaxis of a population of cells. Unlike other magnetotactic bacteria which appear to passively align along the geomagnetic field lines when swimming, MO-1 cells seem to constantly detect and adapt their swimming direction. Using a specific developed magnetic device and the magnetotaxis assessing method, we have demonstrated that the MO-1 cells swim persistently in parallel to magnetic field lines at a velocity up to 350 µm/s. The MO-1 cells have two flagellar bundles which use both sodium-ion and proton driven motors. Proteomic analyses allowed us to identify three glycosylated flagellin proteins. The mechanism of the glycosylation remains to be elucidated. -------------------------------------------------------------------------------- S351minaires de Minéralogie --------------------------------------------------------------------------------