Improved method of determining muramic acid from environmental samples

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Abstract
Muramic acid is an amino sugar that forms part of the peptidoglycan in prokaryotic cell walls. Since muramic acid is found only in prokaryotes it has been used as a measure of bacterial and cyanophyte biomass. Successful application of sensitive capillary gas‐liquid chromatographic (GLC) analysis required neutralization of the acid‐hydrolysate of a biomass sample followed by centrifugation to remove humic acids. After a further fractionation on a cation exchange column followed by derivatization and GLC analysis, recoveries of 98 ±9.5 (X± S.D.) % of authentic muramic acid from estuarine sediments with sensitivities of 10‐13 mol were achieved. The structure of the GLC derivative was established by GLC infrared analysis and GLC mass spectrometry. The improvements in reproduci‐bility and sensitivity have allowed detection of 13C enrichments in muramic acid from the detrital microbiota incubated with relabeled precursors.