Na+ and flagella-dependent swimming of alkaliphilic: a basis for poor motility at low pH and enhancement in viscous media in an “up-motile” variantBacillus pseudofirmus: a basis for poor motility at low pH and enhancement in viscous media in an “up-motile” variantOF4: a basis for poor motility at low pH and enhancement in viscous media in an “up-motile” variant

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Abstract

Flagella-based motility of extremely alkaliphilic Bacillus species is completely dependent upon Na+. Little motility is observed at pH values < ˜8.0. Here we examine the number of flagella/cell as a function of growth pH in the facultative alkaliphile Bacillus pseudofirmus OF4 and a derivative selected for increased motility on soft agar plates. Flagella were produced by both strains during growth in a pH range from 7.5 to 10.3. The number of flagella/cell and flagellin levels of cells were not strongly dependent on growth pH over this range in either strain although both of these parameters were higher in the up-motile strain. Assays of the swimming speed indicated no motility at pH < 8 with 10 mM Na+, but significant motility at pH 7 at much higher Na+ concentrations. At pH 8-10, the swimming speed increased with the increase of Na+ concentration up to 230 mM, with fastest swimming at pH 10. Motility of the up-motile strain was greatly increased relative to wild-type on soft agar at alkaline pH but not in liquid except when polyvinylpyrrolidone was added to increase viscosity. The up-motile phenotype, with increased flagella/cell may support bundle formation that particularly enhances motility under a subset of conditions with specific challenges.

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