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.