Efficacy of phospholipid analysis in determining microbial biomass in sediments

Improvements in the analysis of lipid-bound phosphates resulted in a simplified and sensitive method for determining microbial biomass in sediments. Sensitivity was enhanced over previous methods by use of a dye, malachite green, which when complexed with phosphomolybdate at low pH has a high extinction coefficient (at 610 nm). The use of a persulfate oxidation technique to liberate phosphate from lipids increased the simplicity and safety of the method relative to the traditional perchloric acid digestions. The modified method was both accurate (yielding quantitative recoveries of cells added to sediments) and precise (coefficient of variation of less than 5% for cells and sediments). A comparison with an epifluorescence technique indicated that the analysis of lipid-bound phosphate was more rapid and less tedious and could be successfully applied to a wider variety of sediment types. An estimate of the lipid-bound phosphate-to-carbon conversion factor based on a diverse enrichment culture from sediments suggested that previous factors for pure cultures may have been too low.