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Figure 1: (a) Membrane fracture uncovering the inner cell membrane (CMi of Synechococcus sp. strain WH8113) showing a dense
distribution of intramembrane particles. Fracture plane then crosses the surface layer (S) into the surrounding medium showing
spicules (arrowhead) that extend from the cell surface. Arrow shows fi ber extending from outer membrane to cell membrane. Scale
bar, 100 nm. (b) Synechococcus (strain WH8113). Complementary fracture plane showing the outer leafl et of the cell membrane
(CMo) which has fewer intramembrane particles than the inner leafl et. The fracture then crosses to the outer leafl et of the outer
membrane (OMo), and then turns to fracture across the surface layer (S). Scale bar, 100 nm. With the kind permission of A.D.T.
Samuel, Rowland Institute for Science, Cambridge, Massachusetts, USA and Department of Molecular & Cell Biology, Harvard
University, Cambridge, Massachusetts, USA [Samuel et al. (2001) BMC Microbiol . 1: 4. doi: 10.1186/1471-2180-1-4].
would allow the cell to swim at speeds of 25 µm s -1 . Wave generation is explained by the expansion
and contraction of the local regions of the outer membrane producing thrust in such a manner that
the cell moves in the direction of the wave (Brahamsha, 1999). There are no experimental evidences
presented in favour of this model. However, the energy required for swimming has been suggested
to be available either through sodium pump operating in the membrane or due to the existence of
calcium channels. Willey et al . (1987) reported a defi nite requirement of sodium for swimming in
Synechococcus sp. strain WH8113 as the swimming was directly proportional to the concentration
of sodium in the medium and it was shown that concentrations below 10 mM, the organism was
immotile. Sodium motive force exhibited a direct correlation with external concentration of sodium
while proton motive force, electrical potential, the proton diffusion gradient and sodium diffusion
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