, 1992; Pinkart
et al., 1996; Ramos et al., 1997). Several reports suggested that the amount of trans-UFAs could be influenced by the cyclopropane content of the membrane (Härtig et al., 2005; Pini et al., 2009). However, we have shown here that the amount of trans-UFAs after, for example toluene stress (Table 2), was similar in the wild-type strain (5.4) and in the cfaB mutant (6.2), suggesting that the CTI has a similar activity level in both strains. selleck chemicals llc Similarly, the proportion of CFAs did not change in the absence of CTI and when cells were subjected to different stresses at the stationary phase of growth (when the content of CFAs was high), the presence of trans-UFAs was still observed. Thus, we suggest that CTI and CFA synthase do not directly compete for their common substrate and that other mechanisms likely regulate the CFA content in the membranes. In E. coli, CFA synthase is subjected to proteolytic cleavage (Chang et al., 2000). The fact that the introduction of plasmid pCEC-3 (which
expresses cfaB from a plasmid promoter) in P. putida BIBF-1120 did not significantly increase the CFA content in the membranes during the exponential phase of growth (Pini et al., 2009), together with the gratuitous induction of cfaB expression in the presence of phenylacetate, suggests that the CfaB enzyme is being synthesized, but rapidly degraded by proteolysis. The results presented in this work confirm that, in contrast to the observations in E. coli, in which a sigma-70 and a RpoS promoter overlap and contribute to the transcription of the cfaB gene (Wang & Cronan, 1994), in P. putida KT2440, there is a single transcriptional start point and that the expression of the cfaB promoter is fully dependent on the RpoS sigma factor. The nature of this promoter was Linifanib (ABT-869) dissected through the identification of four nucleotides in the −10 region that are necessary for high expression of the cfaB promoter. Despite the fact that CFA synthase and CTI utilize the same cis-UFAs as
substrates, the levels of trans-UFAs or CFAs in the membranes of mutants deficient in CTI or CFA synthase are not significantly different from those in the parental strain. This work was supported by FEDER-supported Consolider-C (BIO2006-05668) from the Ministry of Science and Innovation and FEDER-supported Junta de Andalucía project of Excelence (Ref: CVI3010). We acknowledge the support of an Intramural CSIC Project (200440E571). C.P. was supported by a scholarship from the BCSH and the CSIC. We thank Dr E. Duque for the gift of the P. putida KT240 cti mutant and Dr M.I. Ramos-González for the P. putida C1R1 mutant. We thank C. Lorente and M. M. Fandila for secretarial support and Ben Pakuts for checking the English.