Cyclopropane fatty acids are involved in organic solvent tolerance but not in acid stress resistance in Pseudomonas putida DOT-T1E.
Bottom Line: Bacterial membranes constitute the first physical barrier against different environmental stresses.Pseudomonas putida DOT-T1E accumulates cyclopropane fatty acids (CFAs) in the stationary phase of growth.The cfaB mutant was also as tolerant as the parental strain to a number of drugs, antibiotics and other damaging agents.
Affiliation: Environmental Protection Department, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, C/Profesor Albareda 1, 18008-Granada, Spain.Show MeSH
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Mentions: The higher levels of CFA during the stationary phase suggested that cfaB expression might be governed by the RpoS sigma factor. To test this hypothesis we first determined the transcriptional start point of the cfaB gene, which was found 53 nucleotides upstream from the ATG start codon (Fig. 3). Around the −10 region we found a sequence that resembled that proposed to be recognized by RNA polymerase/σ38 (5′‐CTACTCT‐3′). To further study the expression of the cfaB gene we fused the cfaB promoter region to 'lacZ to yield plasmid pMPcfaB. Figure 4 shows that expression of the cfaB gene was clearly dependent on the growth phase, with a sharp increase in expression when the culture entered the late‐exponential phase and persistently high levels throughout the stationary phase. The response of the cfaB promoter was totally different to that of the promoter of the efflux pump TtgGHI (Fig. 4) in which no increase in expression was observed during stationary phase. This increase in expression, together with the finding of a −10 region with high similarity to a consensus sequence for σ38, indicated that expression of the cyclopropane synthase gene was tightly controlled by RpoS. To verify the role of RpoS in the expression of cfaB we introduced plasmid pMPcfaB into a P. putida rpoS ‐deficient strain. Expression of the cfaB promoter was completely shut down in this genetic background (not shown), confirming that RpoS is the sigma factor responsible for transcription of the cfaB gene of P. putida DOT‐T1E. At the same time as expression of β‐galactosidase was measured, we determined CFA levels in the cells, and found that in the wild‐type strain CFAs became detectable as cfaB expression increased, whereas no C17:CFA was detected in the rpoS mutant background at any time.
Affiliation: Environmental Protection Department, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, C/Profesor Albareda 1, 18008-Granada, Spain.