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 Previous Article

Journal of Bacteriology, June 2000, p. 3314-3318, Vol. 182, No. 11
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

A Slow-Motility Phenotype Caused by Substitutions at Residue Asp31 in the PomA Channel Component of a Sodium-Driven Flagellar Motor

Seiji Kojima,dagger Tomokazu Shoji, Yukako Asai, Ikuro Kawagishi, and Michio Homma*

Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan

Received 3 January 2000/Accepted 17 March 2000

PomA is thought to be a component of the ion channel in the sodium-driven polar-flagellar motor of Vibrio alginolyticus. We have found that some cysteine substitutions in the periplasmic region of PomA result in a slow-motility phenotype, in which swarming and swimming speeds are reduced even in the presence of high concentrations of NaCl. Most of the mutants showed a sodium ion dependence similar to that of the wild type but with significantly reduced motility at all sodium ion concentrations. By contrast, motility of the D31C mutant showed a sharp dependence on NaCl concentration, with a threshold at 38 mM. The motor of the D31C mutant rotates stably, as monitored by laser dark-field microscopy, suggesting that the mutant PomA protein is assembled normally into the motor complex. Mutational studies of Asp31 suggest that, although this residue is not essential for motor rotation, a negative charge at this position contributes to optimal speed and/or efficiency of the motor.

* Corresponding author. Mailing address: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan. Phone: 81-52-789-2991. Fax: 81-52-789-3001. E-mail: g44416a{at}nucc.cc.nagoya-u.ac.jp.

dagger Present address: Department of Biology, University of Utah, Salt Lake City, UT 84112.

Journal of Bacteriology, June 2000, p. 3314-3318, Vol. 182, No. 11
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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