Two types of Bacillus subtilis tetA(L) deletion strains reveal the physiological importance of TetA(L) in K+ acquisition as well as in Na+, alkali, and tetracycline resistance

The chromosomally encoded TetA(L) protein of Bacillus subtilis is a multifu nctional tetracycline-metal/H+ antiporter that also exhibits monovalent cat ion/H+ antiport activity and a net K+ uptake mode. In this study, B. subtil is mutant strains JC112 and JC112C were found to be representative of two p henotypic types of tetA (L) deletion strains that are generated in the same selection. Both strains exhibited increased sensitivity to low tetracyclin e concentrations as expected. The mutants also had significantly reduced ab ility to grow in media containing low concentrations of K+, indicating that the net K+ uptake mode is of physiological consequence; the deficit in JC1 12 was greater than in JC112C, JC112 also exhibited (i) greater impairment of Na+- or K+-dependent growth at pH 8.3 than JC112C and (ii) a greater deg ree of Co+2 as well as Na+ sensitivity. Studies were initiated to explore t he possibility of two different patterns of compensatory changes in other i on-translocating transporters in these mutants. Increased expression of two loci has thus far been shown. Increased expression of czcD-trk-A, a locus with a proposed involvement in K+ uptake, occurred in both mutants. The inc rease was highest in the presence of Co2+ and was higher in JC112 than in J C112C. Deletion of czcD-trkA resulted in diminished growth of the wild-type and both mutant strains at low [K+], supporting a significant role for thi s locus in K+ uptake. Expression of yheL, which is a homologue of the Na+/H + antiporter-encoding nhaC gene from Bacillus firmus OF4, was also increase d in both tetA(L) deletion strains, again with higher up-regulation in JC11 2. The phenotypes resulting from deletion of yheL were consistent with a mo dest role for YheL in Na+-dependent pH homeostasis in the wild type. No maj or role for YheL was indicated in the mutants in spite of the overexpressio n. The studies underscore the multiple physiological functions of TetA(L), including tetracycline, Na+, and alkali resistance and K+ acquisition. The studies also reveal and begin to detail the complexity of the response to m utational loss of these functions.