Expression of the endogenous type II secretion pathway in Escherichia colileads to chitinase secretion

Escherichia coli K-12, the most widely used laboratory bacterium, does not secrete proteins into the extracellular medium under standard growth condit ions, despite possessing chromosomal genes encoding a putative type II secr etion machinery (secreton). We show that in wild-type E.coli K-12, divergen t transcription of the two operons in the main chromosomal gsp locus, encod ing the majority of the secreton components, is silenced by the nucleoid-st ructuring protein H-NS. In mutants lacking H-NS, the secreton genes cloned on a moderate-copy-number plasmid are expressed and promote efficient secre tion of the endogenous, co-regulated endochitinase ChiA. This is the first time that secretion of an endogenous extracellular protein has been demonst rated in E.coli K-12.