Regulation of extracellular protease secretion in Pseudomonas maltophilia

Cells grown in minimal medium and harvested in late exponential phase secreted extracellular protease linearly when suspended at high density in fresh medium. If the cells were suspended with 0.2% (wt/vol) yeast extract and no additional carbon source, the rate of exoenzyme production was increased several-fold. When pyruvate, L-malate, succinate, or alpha-ketoglutarate was added, repression of exoenzyme secretion was observed. The most effective repressor was alpha-ketoglutarate. These compounds were also preferred substrates for growth of Pseudomonas maltophilia. The data suggest that exoenzyme secretion is controlled by a mechanism similar to catabolite repression. In support of this was the observation that alpha-ketoglutarate repressed exoenzyme secretion preferentially with respect to total protein synthesis. The addition of inhibitors that affect protein synthesis indicated that exoenzyme secretion is several times more sensitive than is total protein synthesis. The addition of chloramphenicol and rifamycin-SV to actively secreting cell suspensions suggested that de novo protein synthesis is required, but that exoenzyme secretion may be supported for at least 30 min in the absence of messenger synthesis. Rifamycin-insensitive protease secretion could be reversed by either alpha-ketoglutarate or chloramphenicol, suggesting that alpha-ketoglutarate is coupled to a post-transcriptional control mechanism.