Chemotactic responses to an attractant and a repellent by the polar and lateral flagellar systems of Vibrio alginolyticus

Chemotactic responses in Vibrio alginolyticus, which has lateral and polar flagellar systems in one cell, were investigated. A lateral-flagella-defective (Pof(+) Laf(-)) mutant, which has only a polar flagellum, usually swam forward by the pushing action of its flagellum and occasionally changed direction by backward swimming. When the repellent phenol was added, Pof(+) Laf(-) cells moved frequently forward and backward (tumbling state). The tumbling was derived from the frequent changing between counter-clockwise and clockwise (CW) rotation of the flagellar motor, as was confirmed by the tethered-cell method. Furthermore, we found that the tumbling cells did not adapt to the phenol stimulus. When the attractant serine was added, the phenol-treated cells ceased tumbling and swam smoothly, adapting to the attractant stimulus after several minutes. We isolated chemotaxis-defective (Che(-)) mutants from the Pof(+) Laf(-) mutant; the tumbling mutants were not isolated. One interesting mutant swam backwards continuously, with its flagellum leading the cell and its flagellar motor rotating CW continuously. A polar-flagella-defective mutant (Pof(-) Laf(+)) stopped swimming after phenol addition and then recovered swimming ability within 10 min, indicating that lateral flagella can adapt to the repellent stimulus. This may represent a functional difference between the two flagellar systems in Vibrio cells, and between the chemotaxis systems affecting the two types of flagella.