A Bacillus flagellar motor that can use both Na+ and K+ as a coupling ion is converted by a single mutation to use only Na+.
In bacteria, the sodium ion (Na(+)) cycle plays a critical role in negotiating the challenges of an extremely alkaline and sodium-rich environment. Alkaliphilic bacteria that grow optimally at high pH values use Na(+) for solute uptake and flagellar rotation because the proton (H(+)) motive force is insufficient for use at extremely alkaline pH. Only three types of electrically driven rotary motors exist in nature: the F-type ATPase, the V-type ATPase, and the bacterial flagellar motor. Until now, only H(+) and Na(+) have been reported as coupling ions for these motors. Here, we report that the alkaliphilic bacterium Bacillus alcalophilus Vedder 1934 can grow not only under a Na(+)-rich and potassium ion (K(+))-poor condition but also under the opposite condition in an extremely alkaline environment. In this organism, swimming performance depends on concentrations of Na(+), K(+) or Rb(+). In the absence of Na(+), swimming behavior is clearly K(+)- dependent. This pattern was confirmed in swimming assays of stator-less Bacillus subtilis and Escherichia coli mutants expressing MotPS from B. alcalophilus (BA-MotPS). Furthermore, a single mutation in BA-MotS was identified that converted the naturally bi-functional BA-MotPS to stators that cannot use K(+) or Rb(+). This is the first report that describes a flagellar motor that can use K(+) and Rb(+) as coupling ions. The finding will affect the understanding of the operating principles of flagellar motors and the molecular mechanisms of ion selectivity, the field of the evolution of environmental changes and stresses, and areas of nanotechnology.
Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan.
Naoya
N
Terahara
Motohiko
M
Sano
Masahiro
M
Ito
D000595:Amino Acid Sequence; D001407:Bacillus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D006863:Hydrogen-Ion Concentration; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D017354:Point Mutation; D011188:Potassium / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012964:Sodium; D012965:Sodium Chloride / Q000494:pharmacology
D001426:Bacterial Proteins; D020409:Molecular Motor Proteins; D012965:Sodium Chloride; D011189:Potassium Chloride; D012964:Sodium; D011188:Potassium