ABSTRACT: We 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 (polystyrene latex beads, diameters 0.126 to 1.5 um) was examined. Mixed bacterial assemblages cultured on BSA media, 2 bacterial isolates, and a natural marine bacterial assemblage hydrolyzed adsorbed ³H-BSA at much slower rates (1/10 to <1/200) than free ³H-BSA. We compared our hydrolysis rates with the predicted collision probabilities between bacteria 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 2 bacterial strains, which appears to be explained by differences in the affinity of bacterial proteases to ³H-BSA. Our results 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.

KEY WORDS: Bacterial degradation . Dissolved organic matter . Adsorption . Colloids

Published in MEPS Vol. 132 (1996) on February 29
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996