RT Journal Article SR Electronic(1) A1 Fenchel, TomYR 1994 T1 Motility and chemosensory behaviour of the sulphur bacterium Thiovulum majus JF Microbiology, VO 140 IS 11 SP 3109 OP 3116 DO https://doi.org/10.1099/13500872-140-11-3109 PB Microbiology Society, SN 1465-2080, AB The swimming track of the sulphur/sulphide-oxidizing bacterium Thiovulum majusis a left-handed helix. The cells modulate swimming speed by changing the tangential speed and/or the pitch and radius of the helix. Whether attached (to a mucous thread) or swimming, the spherical cells rotate around their anterior-posterior axis in a counter-clockwise direction when observed from the posterior pole. Swimming speeds may exceed 600 μm s-1, which is 5-6 times faster than recorded for any other bacterium. Thiovulumcells congregate at oxygen tensions of about 4% atmospheric saturation (0.85 kPa). Cells which accidentally leave the optimum zone make a U-turn within 150-200 μm, thus returning to where they came from. This represents a type of phobic response in which the eventual swimming direction is correlated with the initial direction; it is not a true chemotactic response in the sense that the cells can orient themselves in O2-gradients. The 180°-bend of the swimming path is probably accomplished by changes in the rotational velocity component which take place when the cells swim into an adverse environment. The U-turn response allows the bacteria to maintain the characteristic 100-200 μm thick veils which separate the sulphidic and the oxygenated zone in or above sediments. Evidence for a chemosensory response to sulphide could not be found., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/13500872-140-11-3109