Characterization of a novel gene, wosA, regulating FlhDC expression in Proteus mirabilis.

In this study, we describe wosA, a Proteus mirabilis gene identified by its ability to increase swarming motility when overexpressed. At various times during the swarming cycle, the increased expression of wosA resulted in a 4- to 16-fold upregulation of the transcription of flhDC, encoding the master regulator of the flagellar cascade. In turn, the expression of flaA, encoding flagellin, was substantially increased in wosA-overexpressing strains. The overexpression of wosA also resulted in constitutive swarmer cell differentiation in liquid medium, a normally nonpermissive condition. However, in wosA-overexpressing strains, the onset of swarming was not altered. A null wosA allele resulted in a slight decrease in swarming motility. The expression of wosA was growth phase dependent during growth in liquid and on agar plates during swarmer cell differentiation. Increasing the viscosity of liquid medium by the addition of polyvinylpyrrolidone induced swarmer cell differentiation and resulted in a fourfold increase in wosA transcription. A fliL mutation that results in constitutive swarmer cell elongation also increased wosA transcription. In this study, we discuss the possible role of the wosA gene product in signal transduction from solid surfaces to induce swarmer cell differentiation, possibly via alterations in the motor switch complex. This study also suggests that despite constitutive swarmer cell differentiation in wosA-overexpressing strains, there are additional regulatory and/or environmental conditions that may control the onset of swarming migration.