Compound-specific delta13C analysis of individual amino sugars--a tool to quantify timing and amount of soil microbial residue stabilization

There is strong scientific evidence that microbial residues such as amino sugars may be stabilized in soil. However, up to now, no investigation has been carried out to quantify both the amount and timing of such stabilization. This is primarily due to methodological constraints, because it is not possible to differentiate between stabilized (old) and recently produced (new) amino sugars when these biomarkers are conventionally analyzed, e.g. by means of gas chromatography and flame ionization detection. Therefore, the aim of the present study was to test whether compound-specific isotope analysis (delta13C) of amino sugars extracted from soil could be used to differentiate between old and new microbial residues. For this aim a method for the delta13C analysis of individual amino sugars was developed and optimized. First results of delta13C values of glucosamine, galactosamine, mannosamine, and muramic acid in soil samples from two different ecological studies are presented, clearly indicating that discrimination between soil inherent and newly formed amino sugars is possible in stable isotope labeling experiments. Our results further showed that, in the short term (within 1 month), only few amino sugars were built, thus making highly 13C-enriched substrates necessary for the quantification of new amino sugar production and for the determination of amino sugar turnover rates.