Sodium Ion Cycle in Bacterial Pathogens: Evidence from Cross-Genome Comparisons

Analysis of the bacterial genome sequences shows that many human and animal pathogens encode primary membrane Na(+) pumps, Na(+)-transporting dicarboxylate decarboxylases or Na(+)-translocating NADH:ubiquinone oxidoreductase, and a number of Na(+)-dependent permeases. This indicates that these bacteria can utilize Na(+) as a coupling ion instead of or in addition to the H(+) cycle. This capability to use a Na(+) cycle might be an important virulence factor for such pathogens as Vibrio cholerae, Neisseria meningitidis, Salmonella enterica serovar Typhi, and Yersinia pestis. In Treponema pallidum, Chlamydia trachomatis, and Chlamydia pneumoniae, the Na(+) gradient may well be the only energy source for secondary transport. A survey of preliminary genome sequences of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Treponema denticola indicates that these oral pathogens also rely on the Na(+) cycle for at least part of their energy metabolism. The possible roles of the Na(+) cycling in the energy metabolism and pathogenicity of these organisms are reviewed. The recent discovery of an effective natural antibiotic, korormicin, targeted against the Na(+)-translocating NADH:ubiquinone oxidoreductase, suggests a potential use of Na(+) pumps as drug targets and/or vaccine candidates. The antimicrobial potential of other inhibitors of the Na(+) cycle, such as monensin, Li(+) and Ag(+) ions, and amiloride derivatives, is discussed.