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

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 L21), 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. Amino sugars are often considered to be abundant components of marine organic matter, yet there are surprisingly few measurements of amino sugars in the marine environment. Chitin, a structural polymer of the amino sugar Nacetyl-glucosamine, is produced by a large variety of marine organisms (Muzzarelli 1977), and the production of chitin in the oceans is undoubtedly quite large. Kirchman and White (1999) estimated that about 10% of marine bacterial production could be supported by chitin. In addition to chitin and its derivatives, amino sugars are found in other polysaccharides, glycoproteins, and glycolipids that are common to many organisms (Sharon 1965). Amino sugars are important structural components of prokaryotic cell walls, where they occur in peptidoglycan, lipopolysaccharides, and pseudopeptidoglycan (Brock et al. 1994). Several studies provide measurements of amino sugars in marine particles and sediments (Ittekot et al. 1984; Müller et al. 1986; Liebezeit 1993; Dauwe and Middelburg 1998), but existing in1 Corresponding author (benner @biol.sc.edu).