Relating the biogeography of nitrogen fixing phytoplankton and the nutrient environment in the ocean
Nitrogen fixation may support as much as half of local productivity in some subtropical regions and is the major source of fixed nitrogen to the ocean, maintaining global productivity on long timescales. We use a combination of numerical models and ecological theory to interpret the relationship of nitrogen fixation and nutrient resources (fixed nitrogen, phosphorus and iron) in the global open ocean. We find that the ratio of the supply rates of iron and fixed nitrogen can accurately predict the biogeography of nitrogen fixers to the extent that it can be constrained by current observations.
Bioremediation of Mixed Chlorinated Solvents by Combining Two Biogeochemical Processes
Chloroethenes are a class of chlorinated solvents which cause extensive soil and groundwater contamination worldwide. They can be detoxified by anaerobic dehalogenating bacteria, in the process of reductive dechlorination. However, chloroethenes are often found mixed with chloromethanes, a class of solvents which inhibit the enzymatic detoxification of chloroethenes by dehalogenating strains. Iron sulfides are powerful chemical reductants for the dechlorination of chloromethanes, and can be generated through the metabolism of iron- and sulfate-reducing bacteria. In this study, a sulfate reducing bacterium was used to produce iron sulfide in the presence of moderate levels of tetrachloroethene and carbon tetrachloride to examine the ability of a sulfate reducing organism to drive reduction of a chloromethane in the presence of chloroethene.
Cultures of the sulfate-reducer Desulfovibrio vulgaris were established in the presence of 100 µM each of tetrachloroethene and carbon tetrachloride. Growth, sulfide formation and chlorinated solvents and their dechlorinated products were monitored. The effects of amorphous iron oxide and cyanocobalamin on the fate of chlorinated solvents compared with unamended control cultures were investigated.
Following growth and sulfide formation, carbon tetrachloride was dechlorinated mostly to carbon disulfide while tetrachloroethene was dechlorinated to trichloroethene and acetylene. Dechlorination rates were enhanced both by the presence of iron and cyanocobalamin separately, and significantly increased when both were present.
This study illustrates the potential to use sulfate reducing bacteria in zones of mixed chlorinated solvent groundwater pollution in order to produce iron sulfide minerals. Their cyanocobalamin-catalyzed action on chloromethanes, coupled with that of dehalogenating strains on chloroethenes is a promising strategy for the bioremediation of such contaminated areas."
Development of an Australian 1,2-Dichloroethane degrading culture
1,2-Dichloroethane (DCA) is one of the most common organochlorine groundwater contaminants worldwide. The successes of bioremediation field studies with organochlorine respiring bacteria have proved the efficacy of the method to degrade such contaminants in situ. The objective of this study was to demonstrate that a DCA degrading consortium, named AusDCA could be used to bioaugment a DCA contaminated acidic aquifer in situ. Functional characterisation experiments of AusDCA in batch cultures showed that the culture could dechlorinate high concentrations of DCA (6.3 mM) to ethene anaerobically at pH 5.5 and pH 6.5 and was not inhibited by approximately 15 µM of chloroform (CF).