Bacterial degradation of protein adsorbed to model submicron particles in seawater

Abstract

We tested the hypothesls that proteln adsorbed to submlcron part~cles In seawater IS more slowly degraded than the same proteln freely d~ssolved Bacterial hydrolysis of methyl-3H-bov~ne serum a l b u m~n ( 3 H -B S~) dlssolved or adsorbed to particles (polystyrene latex beads diameters 0 126 to 1 5 pm) was examlned Mlxed bactenal assemblages cultured on BSA media, 2 bactenal ~solates, and a natural marlne bactelial assemblage hydrolyzed adsorbed 'H-BSA at much slower rates (1/10 to <1/200] than free 'H-BSA We compared our hydrolysls rates wlth the predicted collision probabilities between bactena and 3 H -B S~ freely dlssolved or adsorbed to beads of different diameters These comparisons suggest that the hydrolysls rate is ~nfluenced pnmanly by the transport rate of 'k-I-BSA to bacteria Hydrolysis of adsorbed 3 H -B S~ differed greatly between 2 bactenal strains whlch appears to be explained by differences In the afflnity of bactenal proteases to 3 H -B S~ OUI results support the hypothesls that adsorption onto subm~cron particles greatly reduces degradation rate of protelns and suggest thdt the adsorption of dissol\ied organic matter (DOM) may be a mechanism that temporarily stores lablle DOM in a slowly degrading, seml-labile pool, whlch makes 11 available for export and further modification by geochem~cal processes KEY WORDS-Bacterial degradation Dissolved organlc matter . Adsorption . Collolds INTRODUCTIONThe recent discovery of many detrital colloids and submicron particles in a wide variety of oceanic environments (Koike et al. 1990, Wells & Goldberg 1991 has renewed interests in the role of colloids in biogeochemical cycles of manne environments. These non-living organic collo~ds are much mol-e abundant (10"o 10'' particles ml-l, depending on size) than microorganisms including bacteria and viruses (Ko~ke et al. 1990, Wells & Goldberg 1991) and can represent a significant fraction (10 to 35%) of the organic carbon pool in the oceans (Benner et al. 1992). The chemical nature, sources, sinks, and turnover of colloids have yet to be clarified (Lee & Wakeham 1992, Nagata & Koike 1995).One potentially important role of colloids and submicron particles in oceanic material cycling is that they 'Present address Ocean Research Institute, The University of Tokyo 1-15-1 Mlnami-dal, Tokyo 164, Japan E-mail nagata@ori U-tokyo ac ]p provide large solid surfaces to which dissolved organic matter (DOM) may adsorb. In fact, prevlous studies have shown that adsorption of polymeric DOM such as protein to surfaces in seawater can occur very rapidly (within minutes; Kirchman et al. 1989) and that the adsorption can have substantial effects on degradation rates of organic material (van Loosdrecht et al. 1990, Fletcher 1991). Keil & Kirchman (1994 suggested that DOM adsorbed to colloids was less easily degraded than freely dissolved DOM. They found that dissolved protein aged in filtered seawater 1s abiotically modified to less b~ologically degradable protein in a short period (110 h), an observation that they could ex...

Protection of protein from bacterial degradation by submicron particles

“…This is in contrast to most other studies, which predominantly used solid artificial surfaces. Nagata & Kirchman (1996) found that adsorption to polystyrene beads reduced the availability of protein to bacteria, whereas Taylor (1995) used glass beads and hypothesized that protein adsorbed to surfaces can be as bioavailable as protein in solution. These studies came to different conclusions perhaps because they used surfaces with different hydrophobicities.…”

Adsorption of dissolved free amino acids on colloidal DOM enhances colloidal DOM utilization but reduces amino acid uptake by orders of magnitude in marine bacterioplankton

“…Since polysaccharides have been shown to be the dominant chemically characterizable compound of the oceanic DOM pool (Benner et al 1992, Pakulski & Benner 1994, McCarthy et al 1996, Aluwihare et al 1997, this competition between abiotic adsorption and bacterioplankton uptake might be of considerable biogeochemical significance. Nagata & Kirchman (1996) calculated the surface area of colloids to be in the range of 10 m2 m-"derived from data given in Koike et al 1990 andGoldberg 1991) in the upper mixed layer of the ocean. Similar to our findings, Nagata & Kirchrnan (1996) found lower utilization rates of proteins (bovine serum albumin, BSA) adsorbed to sub-micrometer particles.…”

Temperature induced decoupling of enzymatic hydrolysis and carbon remineralization in long-term incubations of Arctic and temperate sediments

“…For example, structural alterations such as methylation of protein have been shown to impede uptake yet allow for hydrolysis (Keil and Kirchman, 1992), and exposure of DOC to microbial remineralization has been found to increase resistance of otherwise labile protein (Keil and Kirchman, 1994). Furthermore, Nagata and Kirchman (1996) hypothesized that adsorption processes of polymeric organic matter to colloids may lead to the formation of a semi-labile DOC pool which can result in the decoupling of DOC production and rapid bacterial mineralization and, therefore, a net accumulation of recalcitrant DOC (Fig. 6, increasing sizes of boxes 2 and 2 0 ).…”