Bactericidal effect of ADP and acetic acid on Bacillus subtilis

Bacillus subtilis is a ubiquitous soil bacterium used for measuring the beta-lysin activity and in other bioassays, We observed a complete bactericidal effect of ADP on B. subtilis at concentrations of 50-100 mu M at pH values <5.5, which disappeared at pH values above 6, The effect was also found for acetic acid at concentrations >17.4 mu M and similar pH values, ATP, adenosine, and HCl were not bactericidal, We used BCECF-AM, a pH-sensitive probe, and found that the killing of B. subtilis was due to a change in the intracellular pH caused by the passage across the cell membrane of these weak organic acids when incubated with B. subtilis at pH values near the pK. More experiments are needed to determine the biological meaning of these in vitro findings.