RUI: Polyhalomethanes in Marine Waters: The Role of DOC and Extracellular Bromoperoxidase

California State University-Long Beach Foundation, Long Beach CA

Investigators

Abstract

ABSTRACT OCE-0350746 Polyhalomethanes produced by marine algae, supply reactive bromine and iodine atoms to the atmosphere where they promote the destruction of both tropospheric and stratospheric ozone, and in the case of iodomethanes, promote the formation of marine aerosols. Polyhalomethanes are indirect products of marine algal haloperoxidase activity, formed as a consequence to destroy toxic H2O2 produced both within and outside their cells. Looking to link algal physiology, marine chemistry and atmospheric science, researchers at the California State University at Long Beach will demonstrate that marine DOC can form polybromo- and polyiodo- methanes catalyzed by algal extracellular bromoperoxidases (BrPO). Measurement of polyhalomethane production will be quantified using a GC-ECD; GC-MS will confirm peak identity. The active DOC fraction(s) will be characterized by their MW size class, using stirred N2-pressurized ultrafiltration. Seawater collected from different coastal locations during the summer and winter will be used to ensure differences in DOC quantity and quality, and will be analyzed for salinity, DOC (high temperature combustion technique) and H2O2 (fluorometric assay). Polybromomethane production from DOC (i.e. ng CHBr3 - biomass-1) by a seaweed and diatom species will be determined from measuring the number of BrPO units present on their surfaces (spectrophotometric assay) and from measuring the rate of polybromomethane production from DOC per commercial BrPO units (similarly defined). Other experiments will directly contrast total polyhalomethane production from these species in seawater of known DOC concentration, to production in seawater in which the DOC has been removed. Comparison of results from these two different methods will allow for the assessment of the significance of this process. This biologically mediated transformation of DOC to polyhalomethanes, which is eventually lost to the atmosphere, is a unique biogeochemical process. Unlike the extracellular enzymes of heterotrophic bacteria that degrade DOC as a source of nutrition (with the production of respiratory CO2), marine algae do not derive any nutritional benefit from the halogenation of DOC and may compete with certain bacteria for the same compounds.