Muramic acid as a measure of microbial biomass in estuarine and marine samples

Muramic acid, a component of the muramyl peptide found only in the cell walls of bacteria and blue-green algae, furnishes a measure of detrital or sedimentary procaryotic biomass. A reproducible assay involving acid hydrolysis, preparative thin-layer chromatographic purification, and colorimetric analysis of lactate released from muramic acid by alkaline hydrolysis is described. Comparison of semitropical estuarine detritus, estuarine muds, and sediments from anaerobic Black Sea cores showed muramic acid levels of 100 to 700 microng/g (dry weight), 34 microng/g, and 1.5 to 14.9 microng/g, respectively. Enzymatic assays of lactate from muramic acid gave results 10- to 20-fold higher. Radioactive pulse-labeling studies showed that [14C]acetate is rapidly incorporated into muramic acid by the detrital microflora. Subsequent loss of 14C, accompanied by nearly constant levels of total muramic acid, indicated active metabolism in procaryotic cell walls.