Inactivation of mdoH leads to increased expression of colanic acid capsular polysaccharide in Escherichia coli

Capsule gene (cps) expression, which normally occurs at low levels in Escherichia coli lon(+) cells, increased 38-fold in lon(+) cells carrying a Tn10::Delta kan insertion mapping to 24 min on the E. coli chromosome. Null mutations in rcsA, rcsB, or rcsC abolished the effect of the Tn10::Delta kan insertion. Sequencing of both sides of the Tn10::Delta kan insertion localized the insertion to the previously reported mdoH gene, which encodes a protein involved in biosynthesis of membrane-derived oligosaccharides (MDOs). A model suggesting that the periplasmic levels of MDOs act to signal RcsC to activate cps expression is proposed.