Marine magnetotactic ovoid bacterium MO-1 is capable of swimming
along the geomagnetic field lines by means of its two sheathed flagellar
bundles at a speed up to 300 μm/s. In this study, by using electron
microscopy, we showed that, in each bundle, six individual flagella were
organized in hexagon with a seventh in the middle. We identified 12
flagellin paralogs and 2 putative flagellins in the genome of MO-1.
Among them, 13 were tandemly located on an ~ 17-kb segment while the
14th was on a separated locus. Using reverse transcription PCR and
quantitative PCR, we found that all the 14 flagellin or putative
flagellin genes were transcribed and that 2 of them were more abundantly
expressed than others. A nLC (nanoliquid chromatography)-ESI
(electrospray ionization)-MS/MS (mass spectrometry/mass spectrometry)
mass spectrometry analysis identified all the 12 flagellin proteins in
three glycosylated polypeptide bands resolved by one-dimensional
denaturing polyacrylamide gel electrophoresis and 10 of them in 21 spots
obtained by means of two-dimensional electrophoresis of flagellar
extracts. Most spots contained more than one flagellin, and eight of the
ten identified flagellins existed in multiple isoforms. Taken together,
these results show unprecedented complexity in the spatial organization
and flagellin composition of the flagellar propeller. Such architecture
is observed only for ovoid-coccoid, bilophotrichously flagellated
magnetotactic bacteria living in marine sediments, suggesting a species
and environmental specificity.
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