Microbial metabolic processes that control the dynamics of high-molecular-weight dissolved organic matter in the ocean

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This study tested the hypothesis that protein adsorbed to submicron particles in seawater is more slowly degraded than the same protein freely dissolved. Bacterial hydrolysis of methyl-^3H-bovine serum albumin (^3H-BSA) dissolved or adsorbed to particles (polystirene latex beads, diameters 0.126-1.5mum) was examined. Mixed bacterial assemblages cultured on BSA media, two bacterial isolates, and a natural marine bacterial assemblage hydrolyzed adsorbed ^3H-BSA at much slower rates (1/10-<1/200) than free 3H-BSA.The measured hydrolysis rates were compared with the predicted collision probabilities between bacteira and ^3H-BSA freely dissolved or adsorbed to beads of different diameters. These comparisons suggest that the hydrolysis rate is influenced primarily by the transport rate of ^3H-BSA to bacteria. Hydrolysis of adsorbed ^3H-BSA differed greatly between two bactirial strains, which appears to be explained by differences in the affinity of bacterial proteases to ^3H-BSA.The results of this study support the hypothesis that adsorption onto submicron particles greatly reduces degradation rate of proteins and suggest that the adsorption of dissolved organic matter (DOM) may be a mechanism that temporarily stores labile DOM in a slowly-degrading, "semi-labile" pool, which makes it available for export and further modification by geochemical processes.