AMINO-ACID EFFLUX IN RESPONSE TO CHEMOTACTIC AND OSMOTIC SIGNALS IN BACILLUS-SUBTILIS

We observed a large efflux of nonvolatile radioactivity from Bacillus subtilis in response to the addition of 31 mM butyrate or the withdraw al of 0.1 M aspartate in a flow assay. The major nonvolatile component s effluxed were methionine, proline, histidine, and lysine, In studies of the release of volatile radioactivity in chemotaxis by B. subtilis cells that had been labeled with [H-3] methionine, the breakdown of m ethionine to methanethiol can contribute substantially to the volatile radioactivity in fractions following addition of 0.1 M aspartate. How ever, methanol was confirmed to be released after aspartate addition a nd, in lesser quantities, after aspartate withdrawal. Methanol and met hanethiol were positively identified by derivitization with 3,5-dinitr o-benzoylchloride. Amino acid efflux but not methanol release was obse rved in response to 0.1 M aspartate stimulation of a cheR mutant of B. subtilis that lacks the chemotaxis methylesterase, The amino acid eff lux could be reproduced by withdrawal of 0.1 M NaCl, 0.2 M sucrose, or 0.2 M xylitol and is probably the result of changes in osmolarity. Ch emotaxis to 10 mM alanine or 10 mM proline resulted in methanol releas e but not efflux of amino acids. In behavioral studies, B. subtilis tu mbled for 16 to 18 s in response to a 200 mosM upshift and for 14 s af ter a 20 mosM downshift in osmolarity when the bacteria were in perfus ion buffer (40 mosM). The pattern of methanol release was similar to t hat observed in chemotaxis. This is consistent with osmotaxis in B. su btilis away from an increase or decrease in the osmolarity of the incu bation medium. The release of methanol suggests that osmotaxis is corr elated with methylation of a methyl-accepting chemotaxis protein.