Use of lipid composition and metabolism to examine structure and activity of estuarine detrital microflora.

Earlier studies have shown that the activity of the estuarine detrital microflora measured by various enzyme activities, muramic acid and adenosine 5'-triphosphate (ATP) content, heterotrophic potentials, and respiratory activities correlates with the incorporation of C and P into the microbial lipids. In this study, these lipids were reproducibly fractionated into neutral lipid, glycolipid, and phospholipid classes. Distinct differences between the active microflora of oak leaves, sweet gum leaves, and pine needles were evidenced both in the rate of lipid synthesis and in the proportions of neutral lipids, glycolipids, and phospholipids. Successional changes in the microflora of leaves incubated in a semitropical estuary, previously suggested by ATP-to-muramic acid ratios and scanning electron micrography, were reflected in changes in the proportions of C in major lipid classes when analyzed from the same type of detritus. Short incubation times with C gave lipid compositions rich in phospholipids that are typical for the faster-growing bacterial populations; longer incubation with C gave lipid compositions richer in neutral and glycolipids, more characteristic of slower-growing eukaryotes or morphologically more complex prokaryotes. The metabolism of the lipids of the estuarine detrital microflora was examined by a pulse-chase experiment with C. Glycolipids lost C at a rate equal to the loss of C of the slow component of muramic acid. Individual phospholipids lost C from their backbone glycerol esters at different rates.