Abundance of amino sugars and peptidoglycan in marine particulate and dissolved organic matter

Abstract

Several recent studies indicated that amino sugars were likely to be major components of marine carbon and nitrogen cycles, but there has been insufficient data to investigate this hypothesis. In the present study, hydrolyzable amino sugars were measured in a variety of marine organisms and particulate organic matter (POM) and in ultrafiltered dissolved organic matter (UDOM) from various ocean basins and depths. Glucosamine (GlcN) and galactosamine (GAlN) were abundant and common to all samples. Concentrations of these two amino sugars were similar to their neutral sugar counterparts, glucose and galactose, and in surface water they accounted for up to ∼1.5% of C and N in POM and 2.5% of C and 7.1% of N in UDOM. Chitin, a polymer of glucosamine, is produced by many marine organisms, but based on the low GlcN :GalN ratios (1.0-2.5) in POM and UDOM, it does not appear to be a primary source of glucosamine in these samples. Muramic acid, an amino sugar found only in the bacterial cell wall polymer peptidoglycan, was relatively abundant in POM, indicating that bacterial detritus is a principal component of submicron particles in seawater. Muramic acid was measured in all UDOM samples, but its concentrations were low (<1 nmol L-1), indicating that intact fragments of peptidoglycan were a relatively minor component of UDOM. The abundance of GlcN and GalN and their similar concentrations in POM and UDOM provide novel information suggesting a major prokaryotic source.