Laboratory and Field Studies
(Hoffmann, Hering, Nealson, Newman)

The availability of trace elements can have profound effects on ecosystem structure and productivity; complex feed-back loops between trace element supply, primary productivity, and biologically-mediated environmental changes have been proposed. Significant fundamental questions regarding sources of trace elements to remote areas, speciation of trace elements and the effects of speciation on bioavailability, the physiological and biochemical responses of organisms to trace element limitation and toxicity and the adaptation of organisms in response to such stresses remain to be addressed and are the focus of current or planned research projects.

    The Hoffmann group has identified seasonal patterns in aolian delivery of iron and other trace metals to the Indian Ocean and has found correlations between dimethyl sulfide production and iron deposition. The Hering group has investigated the redox cycling of the toxic trace element arsenic in geothermally-influenced surface waters and has found the rapid oxidation of arsenite to arsenate to be microbially-mediated. Further work is being conducted, in collaboration with Dr. Nealson, to characterize the microorganisms responsible for arsenite oxidation, to develop 16s-rRNA probes that can be used to identify them, and to determine whether arsenite oxidation is involved in detoxification or in energy acquisition. The Hering and Nealson groups are also collaborating on the study of metal acquisition by photosynthetic organisms in extreme alkaline environments.

    As Head of the Astrobiology Group at JPL, Dr. Nealson is also heading a intensive investigation on the signatures that the biota leaves on its environment and has left in the geologic record. These researchers will be joined in Fall 1999 by Dr. Newman whose research interests include the processes of biomineralization and biofilm formation.