EXPRESSION OF EXTRACELLULAR PHOSPHOLIPASE FROM SERRATIA-LIQUEFACIENS IS GROWTH-PHASE-DEPENDENT, CATABOLITE-REPRESSED AND REGULATED BY ANAEROBIOSIS

Many members of the genus Serratia synthesize and excrete a number of extracellular hydrolytic enzymes. One of these is the phospholipase A1 from Serratia liquefaciens, the expression of which is growth-phase-dependent. Through the use of gene fusions and primer extension analysis we show that the expression of phospholipase is subject to positive transcriptional regulation of a dual promoter system; one promoter positioned approximately 600 bp upstream from the phIA gene is responsible for the induction of phospholipase expression under anaerobic conditions, and the other promoter positioned 50 bp upstream from the phIA gene is subject to catabolite repression and induced during the transition from exponential to late log-phase of bacterial growth. On the basis of sequence homology and behaviour in the relevant Escherichia coli mutants, we suggest the distant promoter to be Fnr-controlled and the proximal phIA promoter to be a member of the FIbB-controlled flagellar-chemotaxis regulon.