Na+(Li+)/H+ antiporter in Pseudomonas aeruginosa and effect of Li+ on cell growth

Everted membrane vesicles were prepared from cells of Pseudomonas aeruginosa, and cation/H+ antiport was measured. We observed activities of Na+/H+ antiport, Li+/H+ antiport and K+/H+ antiport. Judging from the competition pattern, it seems that there are at least two types of antiporter, a Na+ (Li+)/H+ antiporter and a K+/H+ antiporter. Na+ was a good substrate for the Na+ (Li+)/H+ system, whereas Li+ was a poor substrate. Although the K-m value for Na+ (or Li+) was similar to those in Escherichia coli Na+/H+ antiporters, the V-max value for Na+ (or Li+) was much smaller in the P. aeruginosa antiporter than in the E. coli antiporters. Growth of P. aeruginosa was strongly inhibited by 0.4 M LiCl, but not by NaCl or KCl.