Tetradecyltrimethylammonium inhibits Pseudomonas aeruginosa hemolytic phospholipase C induced by choline

Pseudomonas aeruginosa expresses hemolytic phospholipase C (PlcH) with choline or under phosphate-limiting conditions. PlcH from these conditions were differently eluted from the Celite-545 column after application of an ammonium sulfate linear reverse gradient. The PlcH from supernatants of bacteria grown in the presence of choline was eluted with 30% ammonium sulfate and was more than 85% inhibited by tetradecyltrimethylammonium. PlcH from supernatants of bacteria grown with succinate and ammonium ions in a low-phosphate medium was eluted as a peak with 10% of salt and was less than 10% inhibited by tetradecyltrimethylammonium. PlcH from low phosphate was purified associated with a protein of 17 kDa. This complex was dissociated and separated on a Sephacryl S-200 column with 1% (w/v) sodium dodecyl sulfate. After this dissociation, the resulting protein of 70 kDa, corresponding to PlcH, was inhibited by tetradecyltrimethylammonium, showing a protection effect of the accompanying protein. RT-PCR analyses showed that in choline media, the plcH gene was expressed independently of plcR. In low-phosphate medium, the plcH gene was expressed as a plcHR operon. Because plcR encodes for chaperone proteins, this result correlates with the observation that PlcH from supernatants of bacteria grown in the presence of choline was purified without an accompanying protein. The consequence of the absence of this chaperone was that tetradecyltrimethylammonium inhibited the PlcH activity.