Improved method using muramic acid to estimate biomass of bacteria in sediments.

A method, which depends on the measurement of muramic acid content to estimate bacterial biomass, has been improved in sensitivity by two orders of magnitude. It is now applicable to any aquatic sediment, whereas previously it was mainly useful in the analysis of gut contents of deposit-feeding animals. Reduced NAD, a product of the oxidation of d-lactate derived from muramic acid, is assayed using bacterial luciferase. The amount of muramic acid in a number of terrestrial and marine bacteria was measured, and found to be lower than that obtained with the previous, less specific, assay procedure. The muramic acid content of a blue-green alga has been measured, thus allowing blue-green algae to be taken into account when estimating bacterial biomass. Experimental evidence is presented which shows that muramic acid in cell wall fragments of bacteria is rapidly degraded by microorganisms in a marine sediment.