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

Abstract

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