The aprX-lipA operon of Pseudomonas fluorescens B52: a molecular analysis of metalloprotease and lipase production

Extracellular protease and lipase production by psychrotrophic strains of P seudomonas fluorescens is repressed by iron and regulated by temperature. T he regulation of protease and lipase has been investigated in P. fluorescen s B52, Whereas lipase production is increased below the optimum growth temp erature ('low-temperature regulation'), protease production was relatively constant and only decreased above the optimum growth temperature. The genes encoding protease (aprX) and lipase (lipA) are encoded at opposite ends of a contiguous set of genes which also includes protease inhibitor, Type I s ecretion functions and two autotransporter proteins. Evidence is presented indicating that these genes constitute an operon, with a promoter adjacent to aprX which has been identified by S1 nuclease analysis. The regulation o f aprX and lipA has been investigated at the RNA level and using lacZ fusio n strains. Whereas the data are consistent with iron regulation at the tran scriptional level, a lipA'-'lacZ fusion is not regulated by temperature, su ggesting that temperature regulation is post-transcriptional or post-transl ational. The possibility of regulation at the level of mRNA decay is discus sed.