Abstract
We have shown previously that Escherichia coli K92 produces two different capsular polymers known as CA (colanic acid) and PA (polysialic acid) in a thermoregulated manner. The complex Rcs phosphorelay is largely related to the regulation of CA synthesis. Through deletion of rscA and rscB genes, we show that the Rcs system is involved in the regulation of both CA and PA synthesis in E. coli K92. Deletion of either rcsA or rcsB genes resulted in decreased expression of cps (CA biosynthesis cluster) at 19°C and 37°C, but only CA production was reduced at 19°C. Concerning PA, both deletions enhanced its synthesis at 37°C, which does not correlate with the reduced kps (PA biosynthesis cluster) expression observed in the rcsB mutant. Under this condition, expression of the nan operon responsible for PA catabolism was greatly reduced. Although RcsA and RcsB acted as negative regulators of PA synthesis at 37°C, their absence did not reestablish PA expression at low temperatures, despite the deletion of rcsB resulting in enhanced kps expression. Finally, our results revealed that RcsB controlled the expression of several genes (dsrA, rfaH, h-ns and slyA) involved in the thermoregulation of CA and PA synthesis, indicating that RcsB is part of a complex regulatory mechanism governing the surface appearance in E. coli.
Highlights
Over 80 distinct capsular or K antigens have been described in Escherichia coli, which are classified into four groups [1]
RcsA and rcsB gene products control colanic acid (CA) synthesis in E. coli K92 at low temperatures We previously showed that E. coli K92 (WT) synthesizes CA as capsular polymers in a temperature-dependent manner [11,21]
It is well known that Rcs phosphorelay and the auxiliary protein RcsA act as positive regulators of CA synthesis [15]
Summary
Over 80 distinct capsular or K antigens have been described in Escherichia coli, which are classified into four groups [1]. Group II K antigens exhibit capsule expression at 37 ◦C but not at low temperatures (18 ◦C) and their regulation is temperature-dependent [1,2]. Transcription of the kps cluster is driven by two convergent temperature-regulated promoters located upstream of regions 1 and 3 [4]. H-NS plays an unusual dual role, being required for maximal transcription at 37 ◦C and contributing to transcriptional repression at low temperatures ( 20 ◦C) [4,6]. Transcription of region 1 is driven by promoter PR1, and its maximal expression at 37 ◦C requires both H-NS and SlyA, whereas a reduced SlyA expression at 20 ◦C results in repressed transcription from PR1
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