Molecular and behavioral analysis of magneto-aerotaxis in Magnetospirillum gryphiswaldense

Magnetotactic bacteria (MTB) contain nanometer-sized crystals of a
magnetic iron mineral enabling directed swimming along geomagnetic
field lines. However, although this unique behavior was discovered
already 40 years ago, it still has remained poorly understood at
the cellular level and the molecular mechanisms responsible for
sensing environmental stimuli and transducing signals to the
flagellar motors have been unknown. Therefore, the major goal of
this thesis was to investigate the swimming behavior of
Magnetospirillum gryphiswaldense both at the behavioral and
molecular level. Individual motors of tethered M. gryphiswaldense
cells were found to rotate both clockwise and counterclockwise with
equal speed. Cells swam at speeds of up to 60 µm s-1 and commonly
displayed runs of several hundred µm in length. In striking
contrast to E. coli, which reorients the cell body between run
intervals at random angles, motor switching events caused swimming
reversals with reorientation angles close to 180°. The sensory
repertoire of M. gryphiswaldense was analyzed by classical
macroscopic chemotaxis assays, and aerotaxis was found to be the
dominant behavior. In addition to the strong microaerophilic
response in oxygen gradients, I observed tactic bands also under
anoxic conditions within gradients of the alternative electron
acceptor nitrate, suggesting that aerotaxis is part of a general
redox or energy taxis mechanism. The aerotactic response of M.
gryphiswaldense was furthermore analyzed by recording and tracking
single cells under controlled atmospheric conditions in a gas
perfusion chamber. Compared to other well-studied bacteria, M.
gryphiswaldense displayed unusually low swimming reversal rates
(