The different capsular polymers in Escherichia coli are divided in four groups (1–4) according to serological, genetic and biochemical criteria (Whitfield, 2006). A few E. coli strains express CPSs belonging to group 2 that contain

polysialic acid (PA). These PAs have been shown to be bacterial pathogenic determinants (Reglero et al., 1993; Rick & Silver, 1996). Other polysaccharides have been described in E. coli that are involved in cellular attachment and biofilm formation. These include colanic acid (CA) (Prigent-Combaret et al., 2000; Whitfield, 2006), which is not usually produced in significant amounts at physiological temperatures (up GS-1101 molecular weight to 30 °C), and provides protection against extreme environmental conditions (Whitfield, 2006). Escherichia coli K92 produces PA as a capsular polymer (Gotschlich et al., 1981; González-Clemente et al., 1990). We have recently observed that it is also able to synthesize CA (Navasa et al., 2009). Moreover, this bacterium reciprocally thermoregulates the formation of both PA and CA. Thus, when E. coli K92 is grown in defined media at 37 °C it produces predominantly PA but at lower temperatures

(below 20 °C) it is not detectable selleck (González-Clemente et al., 1990), whereas synthesis of CA is maximal (Navasa et al., 2009). The chromosomal locus for PA synthesis Telomerase (designated kps) has a conserved structure comprising three regions (Fig. 1a) (Whitfield, 2006). Transcription of the kps locus is driven by two convergent temperature-regulated promoters located upstream of regions 1 (PR1) and 3 (PR3) (Cieslewicz & Vimr, 1996; Stevens et al., 1997). This thermoregulation is a defining feature of group 2 capsules, and although a detailed understanding of the process is not yet available, current information points to a complex and multifactorial system (Rowe et al., 2000). Escherichia coli K92 is

also capable of degrading sialic acid and, similar to E. coli K1 (Rodríguez-aparicio et al., 1987; Vimr et al., 2004), the catabolism genes are included in the chromosomal locus, the nan system (Fig. 1b). The genes encoding the enzymes responsible for the production and transport of CA are clustered in large operons that are largely identical to the group 1 capsule locus (Whitfield & Paiment, 2003). In E. coli, the CPS synthesis gene cluster is termed the wca/cps operon (Fig. 1c). The regulatory system that controls transcription of the CA biosynthesis locus can be activated by growth at lower temperatures (below 30 °C) or under stress conditions (Sledjeski & Gottesman, 1996) and its expression is regulated by a complex signal transduction pathway called the Rcs system (Majdalani & Gottesman, 2005). As yet, E.