, 2009). These results suggest that variations in protein activity but not in protein amounts of the Rcs system could be implicated in CA thermoregulation. Protein activity regulation is based on cascades of phosphorylation/dephosphorylation in response to a variety of environmental stimuli (Majdalani & Gottesman, 2005;
Whitfield, 2006). Indeed, the RcsF protein functions as a signal transducer sensor whose activation does not require increased transcription of the gene (Majdalani et al., 2005). The increase in rcsA gene expression at 19 °C (Table 3), when maximal CA production is achieved (Navasa et al., 2009), suggests that RcsA provides an independent Selleck PD0332991 regulatory component of the Rcs phosphorelay system in E. coli K92 by RcsB binding. This positive effect of RcsA can be aided by the lower expression of the negative regulator h-ns at 19 °C (Table 4). Overall, the reduction of the inhibitory effect exerted by H-NS on rcsA stimulates the transcription of the cps operon. Moreover, the regulatory effect of RcsA on CA synthesis can be positively http://www.selleckchem.com/screening/mapk-library.html modified by the presence of DsrA through inhibition of H-NS expression (Sledjeski & Gottesman, 1995; Majdalani & Gottesman, 2005). Surprisingly, our results showed lower expression of dsrA at the lower temperature (Table 4). The fact that E. coli K92 is capable of thermoregulating
the expression of two different CPSs (CA and PA) mediated by H-NS (Rowe et al., 2000; Majdalani & Gottesman, 2005) suggests that DsrA also participates in the regulation of PA biosynthesis. Thalidomide However, the small difference observed in dsrA expression between 19 and 37 °C suggests that H-NS is a dual regulator of the synthesis of PA and CA: H-NS is upregulated at 37 °C (3.3-fold), mediating PA synthesis, while at 19 °C its lower expression may facilitate the positive action of RcsA on CA synthesis. This hypothesis is consistent with previous studies
that have reported that H-NS plays a dual role in gene expression regulation by temperature as it is necessary for maximal transcription acting together with SlyA on the kps cluster at 37 °C (Corbett et al., 2007; Xue et al., 2009). The highest level of expression observed at 37 °C for slyA (Table 4) is in accordance with such function for SlyA. Moreover, the fact that the rfaH gene is expressed to a greater level at 37 °C (Table 4) supports the notion that RfaH may be involved in the thermoregulation of capsular polymers in E. coli K92, as described for other bacteria (Stevens et al., 1997). Studies of the production of capsular polymers and analysis of the gene expression using knockout E. coli K92 in rcsA, h-ns, dsrA, slyA and rfaH should provide key data to establish the exact role of these genes in the thermoregulatory control of CA and PA. Further research in this regard is currently in progress.