Effects of substrate concentration, growth state, and oxygen availability on relationships among bacterial carbon, nitrogen and phospholipid phosphorus content

Abstract

The utility of phospholipid phosphorus (Plip-P) concentrations as a measure of microbial biomass is dependent upon the accuracy of the conversion factors used for relating Plip-P to cell carbon, nitrogen or weight. Mixed cultures enriched from marine sediments have been used to evaluate the reliability of these relationships as a function of substrate concentration, growth state and the presence of oxygen. Ratios of Plip-P to carbon and nitrogen were independent of growth state and substrate level but were sensitive to oxygen status. For aerobic incubations, average ratios of 190 and 730 μmol Plip-P/g carbon and nitrogen were obtained respectively. Average ratios of 100 and 350 μmol Plip-P/g carbon and nitrogen were obtained from anaerobic incubations. As a result, it is not likely that single conversion factor can be applied to samples from both aerobic and anaerobic systems. In addition, a limited survey of algal Plip-P, carbon and nitrogen concentrations indicates that the presence of a significant algal biomass can result in erroneous estimates of bacterial abundance.