Cellular fatty acid patterns inPseudomonas sp. CF600 during catechol and phenol degradation in media supplemented with glucose as an additional carbon source

Effect of glucose on the fatty acid composition of Cupriavidus necator JMP134 during 2,4-dichlorophenoxyacetic acid degradation: implications for lipid-based stable isotope probing methods

Combining lipid biomarker profiling with stable isotope probing (SIP) is a powerful technique for studying specific microbial populations responsible for the degradation of organic pollutants in various natural environments. However, the presence of other easily degradable substrates may induce significant physiological changes by altering both the rate of incorporation of the target compound into the biomass and the microbial lipid profiles. In order to test this hypothesis, Cupriavidus necator JMP134, a 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading bacterium, was incubated with [(13)C]2,4-D, [(13)C]glucose, or mixtures of both substrates alternatively labeled with (13)C. C. necator JMP134 exhibited a preferential use of 2,4-D over glucose. The isotopic analysis showed that glucose had only a small effect on the incorporation of the acetic chain of 2,4-D into the biomass (at days 2 and 3) and no effect on that of the benzenic ring. The addition of glucose did change the fatty acid methyl ester (FAME) composition. However, the overall FAME isotopic signature reflected that of the entire biomass. Compound-specific individual isotopic analyses of FAME composition showed that the (13)C-enriched FAME profiles were slightly or not affected when tracing the 2,4-D acetic chain or 2,4-D benzenic ring, respectively. This batch study is a necessary step for validating the use of lipid-based SIP methods in complex environments.

Cyclopropane fatty acyl synthase in Sinorhizobium meliloti

Cyclopropane fatty acyl synthases (CFA synthases) are enzymes that catalyse the addition of a methylene group acrosscisdouble bonds of monounsaturated fatty acyl chains in lipids. We have investigated the function of two putative genes,cfa1andcfa2,proposed to code for CFA synthases inSinorhizobium meliloti. Total fatty acid composition and fatty acid distributions within lipid classes for wild-type andcfa1andcfa2mutant strains grown under Pistarvation and in acidic culture conditions were obtained by GC/MS and by infusion ESI/MS/MS, respectively. For wild-type cells and thecfa1mutant, total cyclopropane fatty acids (CFAs) increased by 10 % and 15 % under Pistarvation and acidic conditions, respectively; whereas in thecfa2mutant, CFAs were less than 0.1 % of wild-type under both growth conditions. Reporter gene fusion experiments revealed thatcfa1andcfa2were expressed at similar levels in free-living cells. Thus under the conditions we examined,cfa2was required for the cyclopropanation of lipids inS. melilotiwhereas the role ofcfa1remains to be determined. Analysis of intact lipids revealed that cyclopropanation occurred oncis-11-octadecenoic acid located in either thesn-1 or thesn-2 position in phospholipids and that cyclopropanation in thesn-2 position occurred to a greater extent in phosphatidylcholines and sulfoquinovosyldiacylglycerols under acidic conditions than under Pistarvation. Thecfa2gene was also required for cyclopropanation of non-phosphorus-containing lipids. Principal components analysis revealed no differences in the cyclopropanation of four lipid classes. We concluded that cyclopropanation occurred independently of the polar head group. Neithercfa1norcfa2was required for symbiotic nitrogen fixation.