Microbial consumption

Amon, R. M. W., and R. Benner. 1996. Photochemical and microbial consumption of dissolved organic carbon and dissolved oxygen in the Amazon River system. Geochimica et Cosmochimica Acta 60 1783-1792. 

Another key factor that determines the lability of ambient DOM is exposure to light and UV (see Chapter 10). The majority of the bioassays reported here were conducted in the dark, and, in this sense, they do not mimic the ambient conditions, because the surface water DOM pool is exposed to at least some light through mixing in the water column as it is being degraded by microbes. Even in cases where the DOM was pretreated with UV (Moran et al., 2000), the actual microbial consumption proceeds in the dark with no further exposure. 

Hydrolytic reactions are catalyzed by extracellular hydrolases and mineral surfaces (Chrost, 1990 Hoffman, 1990). For enzymatic reactions, a defined substrate or moiety must match the catalytic site of a specific enzyme. The most studied examples in aquatic systems are glycosidases, peptidases, and phosphatases (Munster and De Hann, 1998 see Chapter 13). In general, hydrolytic reactions break the relatively labile C—N and C—O bonds that link monomers, generating lower molecular weight products more suitable for microbial consumption. 

As one part of a recent investigation of the biogeochemistiy of an estuary, DMS was included (55)- They found that the concentration of DMS increased from 0.3 nM in the river (fresh water) end-member to 2-3 nM nearer the ocean. They suggested that two mechanisms, microbial consumption and volatilization, could beimportant removal processes. 

If DMS concentrations at the surface of the ocean are presumed to be at steady state, production must balance loss. The fate of DMS is thought to be evasion across the sea surface into the marine atmospheric boundary layer. However, since rates of DMS production are unknown, it is impossible to compare production with flux to the atmosphere, which is relatively well constrained. An alternative sink for DMS in seawater is microbial consumption. The ability of bacteria to metabolize DMS in anaerobic environments is well documented (32-341. Data for aerobic metabolism of DMS are fewer (there are at present none for marine bacteria), but Sivela and Sundman (25) and de Bont et al. (25) have described non-marine aerobic bacteria which utilize DMS as their sole source of carbon. It is likely that bacterial turnover of DMS plays a major role in the DMS cycle in seawater. 

Microbial consumption of DMS in the hypolimnion is more difficult to estimate since our laboratory experiments showing degradation have not been rigorous enough to yield degradation rates applicable to natural conditions. However, if we assume that DMS is transported into the hypolimnion by eddy diffusion, with an arbitrary eddy diffusion coefficient of 1 m2/d, the observed concentration gradient across the oxic/anoxic boundary would support a sink for 30 pmol/m2/d DMS produced in the hypolimnion. We therefore hypothesize that anaerobic microbial consumption in the hypolimnion of Salt Pond may be the major sink for DMS produced in the metalimnion. At this point we cannot estimate the potential for DMS oxidation in the epilimnion. 

We observed that for freshly contaminated soil, the compound readily desorbed into the aqueous phase and was available for microbial consumption whereas for soils containing mostly the non-labile material, the contaminant availability was limited by the mass transfer into the aqueous phase. The fraction of contaminant, which is irreversibly bound to soil is typically present in micropores or chemically bound to soil humic matter and thus is not accessible for microbial utilization. These observations are in agreement with those reported for other chemicals in the literature. It is believed that the longer the contaminant age within the soil the lower the fraction of the contaminant that will be bioavailable. The observations have significant implications to the current remedy and the possibility of natural attenuation at the site. 

Arabian Sea show large changes bought about by microbial consumption/produc-tion of these dissolved nitrogen species (Altabet et al, 1999 Brandes et al, 1998 Naqvi et al, 1998a,b Yoshinari et al, 1997). The most pronounced mass-dependent fractionations appear to occur through water column denitrification. Preferential... 

Visscher P. T., Taylor B. F., and Kiene R. P. (1995) Microbial consumption of dimethyl sulfide and methanethiol in coastal marine sediments. FEMS Microbiol. Ecol. 18, 145-154. 

Under anaerobic conditions, microbial consumption of methane may occur by reactions such as ... 

The age of the dissolved organic carbon in the deep ocean supports the concept that below a depth of a few hundred meters the rate of microbial consumption of dissolved organic compounds is very slow. Based on the oxygen consumption rate in deep waters, Postma (81) has calculated a minimum age of 500 years for the dissolved organic matter in the deep sea, while Williams and coworkers (82) have recently... 

Conrad, R., and W. Seiler (1980d). Photooxidative production and microbial consumption of carbon monoxide in seawater. FEMS Microbiol. Lett. 9, 61-64. 

Linear regression analysis showed that the production rates of DMS were closely correlated to DMSPd concentrations in the microlayer (i =0.5563, n=8, P=0.03) as well as in the subsm-face water (i =0.6220, n=8, P=0.02). The DMS production through enzymatic DMSP cleavage generally exceeded its microbial consumption rates, leading to net DMS production. The imbalance in these two processes might be caused by other sink pathways for DMS such as photochemical oxidation and sea-to-air emission. 

When blended with starch beads, PE films [16] deteriorate on exposure to a soil environment. The microbial consumption of the starch component, in fact, leads to increased porosity, void formation, and the loss of integrity of the plastic matrix. 

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