Transcriptional control of RfaH on polysialic and colanic acid synthesis by Escherichia coli K92

•RfaH promotes cps expression for colanic acid synthesis mainly at low temperatures.•RfaH promotes kps expression for polysialic acid synthesis at high temperatures.•RfaH is essential for E. coli K92 growth at low temperatures. The transcriptional antiterminator RfaH promotes transcription of long operons encoding surface cell components important for the virulence of Escherichiacoli pathogens. In this paper, we show that RfaH enhanced kps expression for the synthesis of group 2 polysialic acid capsule in E. coli K92. In addition, we demonstrate for the first time that RfaH promotes cps expression for the synthesis of colanic acid, a cell wall component with apparently no role on pathogenicity. Finally, we show a novel RfaH requirement for growth at low temperatures.