Abstract
Abstract. Amino sugars are quantitatively significant constituents of soil and marine sediment, but their sources and turnover in environmental samples remain poorly understood. The stable carbon isotopic composition of amino sugars can provide information on the lifestyles of their source organisms and can be monitored during incubations with labeled substrates to estimate the turnover rates of microbial populations. However, until now, such investigation has been carried out only with soil samples, partly because of the much lower abundance of amino sugars in marine environments. We therefore optimized a procedure for compound-specific isotopic analysis of amino sugars in marine sediment, employing gas chromatography–isotope ratio mass spectrometry. The whole procedure consisted of hydrolysis, neutralization, enrichment, and derivatization of amino sugars. Except for the derivatization step, the protocol introduced negligible isotopic fractionation, and the minimum requirement of amino sugar for isotopic analysis was 20 ng, i.e., equivalent to ~8 ng of amino sugar carbon. Compound-specific stable carbon isotopic analysis of amino sugars obtained from marine sediment extracts indicated that glucosamine and galactosamine were mainly derived from organic detritus, whereas muramic acid showed isotopic imprints from indigenous bacterial activities. The δ13C analysis of amino sugars provides a valuable addition to the biomarker-based characterization of microbial metabolism in the deep marine biosphere, which so far has been lipid oriented and biased towards the detection of archaeal signals.
Highlights
Amino sugars are significant sedimentary components that are mostly derived from microorganisms and invertebrates
Methods for the carbon isotopic analysis of amino sugars have been developed for soils, but not for marine sediments, where amino sugar concentrations tend to be lower
We tested various steps in the workflow of amino sugar analysis in order to establish a robust protocol for the stable carbon isotopic analysis of amino sugars in marine sediments
Summary
Amino sugars are significant sedimentary components that are mostly derived from microorganisms and invertebrates. The four major amino sugars, glucosamine (GlcN), galactosamine (GalN), mannosamine (ManN) and muramic acid (MurA), accounted for up to 12 % of total organic carbon (TOC) in grassland soils in North America (Amelung et al, 1999) and ∼ 2 % of TOC in coastal Peruvian surface sediments (Niggemann and Schubert, 2006). Prokaryotic biomass is thought to be the major source of GlcN and GalN in marine sediment (e.g., Niggemann and Schubert, 2006; Langerhuus et al, 2012) and seawater (Benner and Kaiser, 2003); most amino sugars in seawater are not likely associated with peptidoglycan (Aluwihare et al, 2005; Aluwihare and Meador, 2008). The investigation of amino sugars has been extended to the marine deep
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