Microbial lipids from a nearshore sediment from Bowling Green Bay, North Queensland: The fatty acid composition of intact lipid fractions

Samples from a sediment core collected in Bowling Green Bay, North Queensland have been analysed for hexane/isopropanol extractable lipids and fatty acids. These data revealed a subsurface lipid abundance maximum at 3–4 cm depth and consistent low total fatty acid abundances (ca 2 μg/g) in the deeper samples ( > 10 cm depth). Lipid phosphate was below the level of detection in all the samples. Bacterial community structure was found to vary markedly in the upper 10 cm of the core, with the 18:1Δ11 bacterial chemotype predominant in the surface sediment and trans-acid chemotypes dominating in the 3–4 cm depth sediment. Based on the fatty acid composition, the bacterial biomass was estimated to vary from 199 μg/g at 3–4 cm depth toca 8 μg/g at 11–13 cm depth, although the fatty acid distributions indicated possible interference from protozoan detritus. In order to test this possibility, a surface sediment sample from a nearby site was extracted and analysed for fatty acids in lipid fractions separated by silica column chromatography. The fatty acid distributions in lipid fractions containing wax/steryl esters, triacylglycerols, glycolipids and phospholipids were markedly different. These analyses were interpreted in terms of fatty acid contributions to the extractable lipids from bacteria, cyanobacteria, protozoan detritus and highly degraded organic matter.