Tatsuo Atsumi

Na+-driven bacterial flagellar motors

Bacterial flagellar motors are the reversible rotary engine which propels the cell by rotating a helical flagellar filament as a screw propeller. The motors are embedded in the cytoplasmic membrane, and the energy for rotation is supplied by the electrochemical potential of specific ions across the membrane. Thus, the analysis of motor rotation at the molecular level is linked to an understanding of how the living system converts chemical energy into mechanical work. Based on the coupling ions, the motors are divided into two types; one is the H+-driven type found in neutrophiles such asBacillus subtilis andEscherichia coli and the other is the Na+-driven type found in alkalophilicBacillus and marineVibrio. In this review, we summarize the current status of research on the rotation mechanism of the Na+-driven flagellar motors, which introduces several new aspects in the analysis.

Amiloride at pH 7.0 inhibits the Na(+)-driven flagellar motors of Vibrio alginolyticus but allows cell growth.

Amiloride, a specific inhibitor for the Na+‐driven flagellar motors of alkalophilic Bacillus, is known to inhibit secondarily the growth of alkalophiles. The motility of a marine Vibrio, V. alginolyticus, was almost completely inhibited by 2 mM amiloride either at pH 7.0 or 8.5. We found that this concentration of amiloride inhibited the cell growth completely at pH 8.5 but only slightly at pH 7.0. Kinetic analysis of the inhibition of motility by amiloride at pH 7.0 showed that the inhibition was competitive with Na+ in the medium. Thus, amiloride at pH 7.0 is really a specific and useful tool for the analysis of the Na+‐driven flagellar motors of Vibro.

Flagellin glycosylation is ubiquitous in a broad range of phytopathogenic bacteria

Glycosylation of flagellin is known to be involved in filament stabilization, motility, and virulence in Pseudomonassyringae. Here we investigated flagellin glycosylation in other phytopathogenic bacteria. Analyses of deduced amino acid sequences, glycostaining, and molecular masses of purified flagellins revealed that flagellins from all phytopathogenic bacteria investigated were glycosylated. Furthermore, the flagellin in a glycosylation-defective mutant of Xanthomonas campestris pv. campestris (Xcc) had a reduced molecular mass, and motility and virulence of the mutant toward host leaves decreased. These results suggest that flagellin glycosylation is ubiquitous in most phytopathogenic bacteria and that flagellin glycosylation is required for virulence in Xcc.

Characterization of polar-flagellar-length mutants in Vibrio alginolyticus

Vibrio alginolyticus has two types of flagella, polar (Pof) and lateral (Laf). From a Laf-defective mutant (Pof+Laf-), polar-flagellar-length mutants which have short Pof and long Pof were isolated. The mean lengths of the helical axis in wild-type, short and long Pof were 5.5.0.9 μm, 2.5.0.6 μm and 11.2.3.6 μm, respectively. The swimming speeds of the short- and long-Pof mutants were slower than that of the wild-type strain. The relationship between swimming speed and flagellar length in a population of mutant cells was examined. In the short-Pof mutant, the decrease of swimming speed seemed to be derived from the decrease in flagellar length. In the long-Pof mutant, there was almost no correlation between swimming speed and flagellar length, and the slow swimming was explained by the helical shape of the flagella, whose pitch and radius were 1.4 μm and 0.062 μm, respectively, whereas those of the wild-type flagella were 1.5 μm and 0.16 μm. The relative amounts of the various molecular components of the long Pof were different from those of the wild-type or the short Pof. This seems to be the reason for the difference in flagellar shape and length, though the mutation may be pleiotropic and affect flagellar function or regulation.