Jorgensen, N. O.G.. Royal Veterinary and Agricultural University, Department of Ecology and Molecular Biology, firstname.lastname@example.org
, . O.G.. ,
L/D RATIOS OF DISSOLVED COMBINED AMINO ACIDS AS INDICATORS OF DOM QUALITY TO BACTERIA
All protein amino acids are L enantiomers but peptidoglycan in bacterial cell walls has a high content of D amino acids. In marine waters, recalcitrant DOM has a L/D ratio of 3 to 4, compared to ratios of 7 to 8 of fresh DOM. In the present study the L/D ratio of selected dissolved combined amino acids (asp, glu and ala) in water samples from an estuary and from batch cultures of marine bacteria was examined and related to the biological activity.
The analyses demonstrated (1) that a high L/D amino acid ratio coincided with a high algal biomass, (2) that bacteria reduced L amino acids in preference to D amino acids, and (3) that estuarine bacteria in stationary growth phase released D amino acids. Thus, L/D ratios of amino acids reflect a balance between production and consumption of both enantiomers. Despite this complex relationship, pronounced seasonal and depth changes of L/D ratios from Roskilde Fjord, Denmark, and the Gulf of Riga, the Baltic Sea, correlated with the primary productivity (increased L/D ratios) and bacterial growth (reduced L/D ratios). Results from the Gulf of Riga suggested that a transiently accumulation of D enantiomers may occur in the summer. More studies are required to understand natural variations of L/D amino acid ratios, but the present results suggest that enantiomer ratios can be a valuable tool for evaluating origin and lability of DOM in natural waters.
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