Isolation from Klebsiella and Characterization of Two rcs Genes That Activate Colanic Acid Capsular Biosynthesis in Escherichia coli

Abstract

Two genes, designated rcs A (regulation of capsule synthesis) and rcsB, that had been cloned from the chromosome of Klebsiella aerogenes (K. pneumoniae) capsular serotype K21 were capable of activating expression of colanic acid capsular polysaccharide in Escherichia coli K12. The Klebsiella rcsA gene encoded a polypeptide of 23 kDa that was required for the induction of a mucoid phenotype at ≤ 30 °C but not at ≥ 37 °C. The Klebsiella rcsB locus encoded no apparent polypeptides and was not capable by itself of causing the overproduction of colanic acid. However, when present in the same cell with rcs A, either in cis or in trans, rcsB caused expression of mucoidy in E. coli at all growth temperatures. These findings are best explained if the Klebsiella rcs A gene product acts as a positive regulator of colanic acid biosynthesis in E. coli and that activity of this protein is in turn subject to regulation by Lon protease. The Klebsiella rcsB locus may exert its effect by preferentially binding a negative regulator of capsular biosynthesis, possibly Lon itself. DNA sequences homologous to the Klebsiella K21 b rcs A and rcsB genes were found in the genomes of all other capsular serotypes of klebsiellae examined, including K2, K12, K36 and K43. However, there was no homology between such genes and the chromosome of E. coli. The ability of these rcs genes to induce a mucoid phenotype explains the apparent conjugative transfer from klebsiellae to E. coli of the ability to produce K21 or other Klebsiella capsular polysaccharides that are structurally and antigenically related to colanic acid.