The focus of work in the Arnosti lab is to combine chemical approaches with aspects of microbiology to investigate the structure and reactivity of macromolecular organic matter and the role of bacterial communities in organic matter degradation. The rationale behind this research is the fact that although most organic matter in marine systems is initially produced as macromolecules whose production and structure are reasonably well understood, the processes by which these macromolecules are transformed and (for the most part) ultimately remineralized by marine microbes are largely unknown. The identities and specific activities of the vast majority of microorganisms which catalyze these processes are also unknown. Microbes play key roles in the transformations, decomposition, and recycling of marine organic carbon, and are believed to be active in nearly all known marine environments, ranging from surface waters to sea ice to anoxic sediments, hydrothermal systems, and the deep biosphere. Microbial responses to organic macromolecules in turn help shape the nature, concentration, and characteristics of organic matter which is preserved, as well as the rate, extent, and location of organic matter remineralization in marine systems. Their activities and interactions therefore are major forces shaping the global carbon cycle.

• Carbon Transformations Under Permanently Cold Conditions

A long-term NSF-funded collaboration with scientists from the Max-Planck Institute for Marine Microbiology (Bremen, Germany) is focused on studying carbon transformations in permanently cold sediments, conditions characterizing ca. 90% of ocean sediments. We seek to determine the means by which sedimentary microbial communities maintain high rates of activity under conditions that inhibit the activities of their more temperate counterparts. Part of this work is a collaboration (Arnosti/Teske labs) to isolate and characterize pure cultures of cold-active, extracellular-enzyme producing bacteria. Fieldwork for this project is conducted on Svalbard, an archipelago in the high Arctic. (Figure 3.7: sampling in Kongsfjorden; Figure 3.8: the Tre Kroner, from the field station in Ny Ålesund, the world’s northernmost permanently inhabited settlement)

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Fig. 3.7                                           Fig. 3.8

• ‘Speed Bumps’ in the Carbon Cycle

Although the importance of microbial communities in the global carbon cycle is undisputed, the rates and specific pathways by which organic carbon is transformed from macromolecules to CO2 are not well understood. This project (NSF and ACS funding) focuses particularly on identifying potential ‘speed bumps’ in carbon remineralization pathways. We are investigating factors that may help control expression, activities, and ‘lifetimes’ of extracellular enzymes, which initiate the degradation of high molecular weight organic carbon in marine systems. We are also investigating carbon flow—from high molecular weight substrates through fermentation to remineralization—in order to identify other possible locations of ‘speed bumps’. Part of this work is being done in collaboration with Dr. Volker Brüchert at the Max-Planck Institute in Bremen. Other aspects of this project—determining the potential influence of surface sorption on enzyme activities and lifetimes—are being carried out in collaboration with Dr. Neil Blough, at the University of Maryland-College Park.

• Biocatalytic Filtration and Carbon Cycling in Permeable Shelf Sediments

In collaboration with Drs. Markus Hüttel (Florida State), Joel Koska (FSU), and Peter Berg (UVA), we are investigating the rates and means of carbon cycling and quantifying organic matter flux through permeable sands. The objective is to determine the role of permeable shelf sediments (70% of continental shelf area) in coastal cycling of carbon and nutrients. Fieldwork for this new NSF-funded project begins in the summer of 2005.

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