USC Dana and David Dornsife College of Letters, Arts and Sciences

Summary Statement of Research Interests

• Abstract From toxic metal pollution to hydrothermal inputs, the geochemistry of an ocean environment shapes the surrounding biological community. Variables include anything from the tolerance/intolerance of a reef organism to withstand a toxin, to geothermal/physicochemical gradients encountered at hydrothermal vents, to sedimentation caused by enhanced runoff. Alteration of surrounding microbial communities can also occur when the influx of trace metals, considered toxins by many organisms, provides energy in the form of electron donors being discharged by hydrothermal systems. On the other end of the spectrum, both microorganisms and macrobenthos can alter chemical species, either as a result of detoxification, or as a consequence of their metabolisms. My research attempts to understand these interactions, focusing on the link between geochemistry and microbiology in marine environments and the feedbacks each has on the other. As ideal models, I target marine shallow-water hydrothermal vent systems, also called shallow-sea vents. I believe these systems offer incredible opportunities for many areas of research related to coastal element cycling, as they are often characterized by steep physicochemical gradients in temperature, pH, HCO3-, and an array of biologically toxic elements such as As, Sb, Se, Cr, Co, Pb, Cd, Ag, Cu, Tl, Zn, Hg, and S, as well as possible limiting nutrients such as Si and Fe. Unlike deep-water systems found at mid-ocean ridges and back-arc environments, hydrothermal venting in shallower depths allow the possibility of utilizing SCUBA diving for sample collection and in situ measurements, and thus remove the complicated use of manned submersibles or ROVs. SCUBA diving plays a major role in my research, as it provides the opportunity for improved, higher resolution, and time series data not possible by conventional means. With an emphasis on trace metal cycling, which includes speciation, microbial utilization, bioavailability, bioaccumulation, and biological synthesis of organic compounds, I investigate the biological/geological interface in these special environments. Expertise In addition to advanced research diving techniques (detailed in my CV), I combine state-of-the-art geochemical analytical methods with molecular- and cultivation-based microbiological techniques to investigate the influence microbes may have on the distribution and ultimate fate of trace elements in the coastal oceans. I embrace a systematic, multidisciplinary approach – emphasizing collaboration with biologists, coastal ecologists, and microbiologists – in order to carry out my research. Thus, while I have the skills and expertise to analyze each geochemical and microbiological aspect of the research, I most often focus on the geochemical analyses while collaborating with microbiologists. Evaluating geochemical/biological interactions on a detailed level begins in the field, with analysis or preservation of unstable geochemical (e.g., T, pH, HCO3, H2S, As species (arsenite, arsenate, organoarsenicals, and thioarsenic species), and intermediate S species) and microbiological (DNA, RNA, culturing) parameters. Geochemical analyses include development and use of custom-built underwater probes, field spectrophotometry (HACH), and filtering/acidification/freezing, depending on the element of interest. Once returning to the laboratory, the geochemical analytical methods I have expertise in using include IC (for analysis of anions and organic acids), ICP-OES (for major salts), ICP-MS (for analysis of major, minor, and trace elements and their isotopes), and GC (for analysis of dissolved gases). Atomic Fluorescence Spectrometry (AFS) allows analysis of hydride forming elements, including arsenic, and hyphenated techniques, such as. HPLC-IC-AFS or HPLC-ICP-MS, allow me to perform trace metal speciation, a critical component of my research for both the geochemical and microbiological aspects. My expertise in microbiological methods, including extraction of DNA and/or RNA from environmental samples, amplification of 16S rRNA genes for construction of clone libraries and phylogenetic trees, and screening for genes related to trace metal redox (e.g., arsenic, sulfur, and nitrogen functional genes), allows for a deeper understanding of these interactions in the context of genetic functioning. I will incorporate pyrotag sequencing and metagenomics for my upcoming research in New Caledonia.