Differences in lipid composition between free-living and initially adhered cells of a Gram-negative bacterium

The phospholipid fatty acid composition and poly-β-hydroxybutyrate (PHB) content of initially adhered and free-living cells of a Pseudomonas sp. isolated from the rape plant Brassica napus were examined with gas chromatography (GC). Five different adhesion experiments were made including variations in surface charge (hydrophilic and lipophilic), temperature, media composition and time of adhesion. Lipids and poly-β-hydroxybutyrate (PHB) were extracted with a chloroform-methanol-water mixture, hydrolyzed and esterified with pentafluorobenzyl bromide. Analysis was performed with capillary gas chromatography and flame ionization detection. A pronounced difference in both the ratio saturated/unsaturated fatty acids and in PHB content between free-living and adhered bacteria were found. The free-living bacteria has a significantly smaller ratio of saturated/unsaturated C₁₆ and C₁₈ fatty acids and also a smaller ratio of total C₁₈/total C₁₆ fatty acids. Bacteria adhered to the lipophilic surface had a higher ratio of saturated to unsaturated C₁₆ fatty acids than at the hydrophilic surface. There were no major differences between the treatments regarding the amount of bacteria adhered to the surface or their lipid composition.