| Summary: | <p>Bacteroidetes gliding motility is a type of surface motility in which rod-shaped
bacteria move up to 2 µm
s
in a corkscrewing motion. Flavobacterium johnsoniae
is the primary model organism for the study of Bacteroidetes gliding. SprB is the
main adhesin in this organism and moves in a helix along the cell surface. This
movement is guided by an underlying track that is anchored to the inner leaflet
of the outer membrane. The essential gliding lipoprotein GldJ, which is helically
arranged when visualised in fixed cells, is suggested to form this track. However,
direct in vivo imaging of GldJ is yet to be achieved. Two currently outstanding
questions about Bacteroidetes gliding motility are 1) how adhesion of SprB to the
substratum is controlled so that binding only occurs when moving from the leading
to the lagging cell pole and 2) how/if the cell discriminate between the poles.
In this thesis, a fusion of the HaloTag domain to SprB enabled labelling of SprB
with stable and bright dyes. The movement of SprB could then be visualised using
single-particle tracking to reveal the underlying track topology. These tracking data
suggest that the underlying track is not a single closed loop currently proposed, but
rather a complex and potentially dynamic structure that can form multiple loops
and cover most of the cell surface.</p>
<p>SprB is encoded by the sprB operon that further encodes RemFG, Fjoh_0982,
and SprCDF. In this thesis I show that all these components, except fjoh_0982,
are required for gliding motility but only sprF are required for SprB helical movement. All the sprB operon components required for gliding are also required for
SprB-mediated attachment to glass, indicating that they regulate adhesion of SprB.
RemG and SprCD move in a helix reminiscent of the SprB movement pattern.
The helical movement does not depend on SprF or SprB, but rather on the SprFhomologous N-terminal domain of SprD. Observations of gliding cells with fluorescently labelled SprC revealed accumulation of SprC near the leading cell pole.</p>
<p>This polar accumulation correlated with the direction of movement and was not
observed in cells that did not move. Furthermore, a mutant lacking the C-terminal
50 residues of SprD was unable to accumulate SprC at the leading pole. SprB did
not show a similar asymmetric distribution in gliding cells.
Fluorescence microscopy shows that helically moving sprB operon proteins accumulate at midcell in dividing cells in a GldJ dependent manner. Cross-linking
mass spectrometry indicates that GldJ interacts with the sprB operon proteins
as well as GldKNO, essential outer membrane components of the type 9 secretion
system which is a pre-requisite for Bacteroidetes gliding motility.</p>
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