Fatty acid composition of bacterial strains associated with living cells of the haptophyte Emiliania huxleyi

Abstract

A number of bacterial strains previously isolated from living cells of the marine haptophyte Emiliania huxleyi and identified from their 16S r-DNA profiles as Dietzia maris sp. S1, Stappia sp. AG2, Nocardioides sp. S3, Sphingomonas sp. AG6, Oceanicaulis alexandrii sp. AG4, O. alexandrii sp. AG7 and Micrococcus sp. AG10 were cultured for examination of their fatty acid (FA) compositions. The total fatty acid (TFA) contents of the different strains ranged from 0.3% to 4% dry wt., which suggests that the use of a single value when converting FA content to estimates of bacterial biomass may have a significant error. A variety of FA distributions was observed, illustrating the diverse patterns in bacteria from marine ecosystems. Some species showed a dominance of saturated and monounsaturated straight chain FAs, while in others iso- and anteiso-branched FAs were the major constituents. The specificity and possible modes of biosynthesis of the unusual constituents, 11-methyloctadec-12-enoic and 10,13-epoxy-11-methyloctadeca-10,12-enoic acids, found in some species, are discussed. Deuterium labelling allowed us to demonstrate that these two compounds arise from the methionine-mediated methylation of cis-vaccenic acid, which supports the previously proposed role of this monounsaturated FA as the precursor of bacterial furan FAs. The strain Sphingomonas sp. AG6 contains C 14–C 16 2-hydroxy acids (strongly dominated by 2-hydroxytetradecanoic acid), which are components of sphingolipid structures linked to sphingosine by amide bonds. 3-Hydroxyacids ranging from C 11 to C 18 were detected in Stappia sp. AG2, O. alexandrii sp. AG4, O. alexandrii sp. AG7 and Micrococcus sp. AG10. These are classical components of cell wall lipopolysaccharides. C 32–C 37 mycolic acids exhibiting an unusually high degree of unsaturation and dominance of odd numbered main chains (>78% of the FAs had a C 21 main chain) were detected in the strain D. maris sp. S1. The data provide further examples of the close association of different types of bacteria with geochemically important algal species.