Identification of an Escherichia coli Operon Required for Formation of the O-Antigen Capsule

Abstract

Escherichia coli produces polysaccharide capsules that, based on their mechanisms of synthesis and assembly, have been classified into four groups. The group 4 capsule (G4C) polysaccharide is frequently identical to that of the cognate lipopolysaccharide O side chain and has, therefore, also been termed the O-antigen capsule. The genes involved in the assembly of the group 1, 2, and 3 capsules have been described, but those required for G4C assembly remained obscure. We found that enteropathogenic E. coli (EPEC) produces G4C, and we identified an operon containing seven genes, ymcD, ymcC, ymcB, ymcA, yccZ, etp, and etk, which are required for formation of the capsule. The encoded proteins appear to constitute a polysaccharide secretion system. The G4C operon is absent from the genomes of enteroaggregative E. coli and uropathogenic E. coli. E. coli K-12 contains the G4C operon but does not express it, because of the presence of IS1 at its promoter region. In contrast, EPEC, enterohemorrhagic E. coli, and Shigella species possess an intact G4C operon.

Self-regulation of exopolysaccharide production in Bacillus subtilis by a tyrosine kinase

“…Consistent with this idea, we show here that the extracellular domain of CapA specifically binds PIA, suggesting that it too is a receptor for controlling exopolysaccharide production in S. aureus. Bacterial tyrosine kinases, such as Wzc and Etk, are also found in Gram-negative bacteria, where they are associated with the pathways for the production of capsular polysaccharides I and IV, respectively (Wugeditsch et al 2001;Peleg et al 2005;Whitfield 2006). It is not obvious, however, how our generalization could apply in cases in which the receptor for the kinase is sequestered in the periplasm and hence unable to interact directly with the environment (Bechet et al 2009).…”

“…Moreover, in several cases, the kinases are known to play a regulatory role in exopolysaccharide production by phosphorylating and thereby activating a biosynthetic enzyme in the pathway for the exopolysaccharide (Grangeasse et al 2007(Grangeasse et al , 2010Bechet et al 2009;Jadeau et al 2012). Thus, in Escherichia coli, the tyrosine kinases Wzc and Etk stimulate production of two kinds of capsular polysaccharides (group I and group IV, respectively) by phosphorylating a uridine diphosphate (UDP)-sugar dehydrogenase in their respective biosynthetic pathways (Wugeditsch et al 2001;Grangeasse et al 2003;Peleg et al 2005;Lacour et al 2008). Likewise, capsular polysaccharide production by Streptococcus thermophilus requires the tyrosine kinase EpsD, which phosphorylates a glycosyltransferase in the biosynthetic pathway (Minic et al 2007).…”

Pivotal Roles of the Outer Membrane Polysaccharide Export and Polysaccharide Copolymerase Protein Families in Export of Extracellular Polysaccharides in Gram-Negative Bacteria

“…It has also been referred to as the gfc (group 4 capsule) locus (101). Recent studies have illustrated a role for this locus in group 4 CPS assembly (also Wzy dependent and essentially a variant of group 1) and in regulation of the heat shock response in E. coli (48,86). The locus contains four other genes, designated ymcABCD, that are duplicated elsewhere on the chromosome in yjbEFGH (31).…”

Overproduction of Exopolysaccharides by an Escherichia coli K-12 rpoS Mutant in Response to Osmotic Stress

“…coli K-12 possesses five known sets of genes promoting EPS production: (i) genes involved in O-antigen synthesis (46); (ii) the wca operon, responsible for colanic acid (CA)-EPS synthesis (19); (iii) the pgaABCD operon which encodes genes involved in the production of poly-␤-1,6-N-acetyl-D-glucosamine (PGA), a polysaccharide shown to be crucial for biofilm formation (59); (iv) the dfc pseudo-operon (comprised of gfcABCDE, etp, and etk), responsible for the production of type IV capsule in E. coli O127:H6 (this operon is nonfunctional in E. coli K-12 due to the presence of an IS1 element in its promoter region [40]); and (v) the yjbEFGH operon, a paralogue of dfcABCD (15).…”