Overproduction of the extracellular lipase is closely related to that of metalloprotease in Serratia marcescens

The recombinant strain of Serratia marcescens Sr41 carrying the lipA gene encoding the extracellular lipase on a high-copy-number plasmid, pUC19, overproduced lipase. The extracellular lipase activity of the hyperproducing strain reached 220,000 U/ml of the culture medium and was about 9-fold greater than that of the strain carrying pUC19. The extracellular protease activity of the lipase-hyperproducing recombinant strain was decreased by 90% compared with that of the strain carrying pUC19. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis revealed overproduction of the lipase and reduction of the extracellular metalloprotease production in the culture medium of the lipase-hyperproducing strain. The production of extracellular metalloprotease was impaired by the increase of lipA gene expression. Thus, construction of the lipase-hyperproducing strain which reduced extracellular metalloprotease production, was achieved by self-cloning of the lipA gene in S. marcescens. The mutants carrying the metalloprotease gene defects constructed by homologous recombination showed significantly elevated extracellular lipase activity. These results suggested that the production of extracellular lipase was closely related to the metalloprotease production and that the secretion of the two proteins may be competitive in S. marcescens.