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CHAD W. SALTIKOV
Assistant Professor of Microbiology and Environmental Toxicology
B.S, University of California, Santa Barbara
Ph.D., University of California, Irvine
Postdoctoral Scholar, California Institute of Technology
Office: 438 PSB (Physical Sciences Building), Office Hours: By
Appointment
Email: saltikov@metx.ucsc.edu
Office Phone: (831) 459-5520
Lab Phone:
(831)459-1885
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Research Group: Saltikov
Lab
Anaerobic microbiology and biotransformation of pollutants and toxic metals.
 Research
Research in my lab focuses on understanding how microbial anaerobic respiratory processes influence the fate and transport of pollutants in the environment with a specific interest in the metalloid arsenic.
Microbial metabolic activity is increasingly thought to play a significant role in controlling the fate and transport of toxic metals in aquatic systems. In the case of arsenic, two primary redox reactions have been described: (i) the oxidation of arsenite (As(III)) to arsenate (As(V)) and (ii) the reduction of As(V) to As(III). Each reaction has different effects on the mobility of arsenic in the environment. In anaerobic sediments, As(V) reduction by bacteria has been shown to promote the mobilization of arsenic into the aqueous environment. The activities of As(V) reducing microbes can ultimately lead to arsenic contamination of groundwater and surface water as observed on a massive scale in Bangladesh and other locales.
Despite the toxicity of As, numerous microbes have been isolated that can grow in the absence of oxygen by coupling the oxidation of organic carbon substrates to the reduction of As(V) to As(III). In the absence of oxygen, As(V) serves as a sole terminal electron acceptor similar to, for example, respiratory nitrate or sulfate reduction. The end result is the formation of reduced arsenic, namely As(III), which is much more toxic than As(V). Consequently, in sedimentary/aquatic systems, As(III) at near neutral pH is uncharged and can readily diffuse into the aqueous environment contaminating well-waters and potentially surface waters used for drinking.
Until recently, the mechanism for As(V) respiratory reduction has remained elusive. Hence, the research in my lab focuses on several aspects of this process, one being investigating the molecular biology and genetics of respiratory As(V) reduction in a representative As(V) respiring bacterium, Shewanella sp. str. ANA-3. My research centers around the recent discovery of an "arsenic island" comprising several gene clusters: an operon for arsenic detoxification (arsDABC) and an operon for As(V) respiratory reduction (arrAB). The ars operon encodes a typical efflux system for the detoxification of arsenic. However, the arrAB cluster is predicted to encode a new class of anaerobic reductases specific for As(V) that allows the cell to conserve energy and grow on As(V) as a sole terminal electron acceptor. The As(V) respiratory reductase gene arrA also appears to be conserved among phylogenetically diverse bacteria.
Current research projects are directed at: (i) constructing a whole-cell model for how bacteria respire As(V), (ii) investigating the diversity of the arrA functional gene, and (iii) applying this molecular biological information to understanding how microbial redox processes affect the As biogeochemical cycle.
Publications:
Reyes, C., Murphy, J.N., and Saltikov, C.W.. (2010) Mutational and gene expression analysis of mtrDEF, omcA, and mtrCAB during arsenate and iron reduction in Shewanella sp. ANA-3. Environ Microbiol. accepted
Zargar, K and Saltikov, C.W.. (2009) Lysine-91 of the tetraheme c-type cytochrome CymA is essential for quinone interaction and arsenate respiration in Shewanella sp. strain ANA-3. Arch Microbiol. 191(11):797-806
Murphy, J.N. and Saltikov, C.W.. (2009) The ArsR repressor mediates arsenite-dependent regulation of arsenate respiration and detoxification operons of Shewanella sp. ANA-3. J Bacteriol. 191(21):6722-6731
Blum, J.S., Han, S., Lanoil, B., Saltikov, C.W., Witte, B, Tabita, F.R., Langley, S., Beveridge, T.J., Jahnke, L., Oremland, R.S.. (2009) Ecophysiology of "Halarsenatibacter silvermanii" strain SLAS-1T, gen. nov., sp. nov., a facultative chemoautotrophic arsenate respirer from salt-saturated Searles Lake, California. Appl Environ Microbiol. 75(7):1950-60
Murphy, J.N., Durbin, J, and Saltikov, C.W.. (2009) Functional roles of arcA, etrA, cyclic AMP (cAMP)-cAMP receptor protein, and cya in the arsenate respiration pathway in Shewanella sp. strain ANA-3. J Bacteriol. 191(3):1035-43
Oremland, R.S, Saltikov, C.W., Wolfe-Simon, F., and Stolz, J.F.. (2009) Arsenic in the Evolution of Earth and Extraterrestrial Ecosystems. Geomicrobiol J.. 26(7):522-536
Tufano, K., Reyes, C, Saltikov, C.W., and Fendorf, S.. (2008) Reductive processes controlling arsenic retention: revealing the relative importance of iron and arsenic reduction. Environ. Sci. Technol. 42(22):8283-9
Reyes, C, Llyod, J, and Saltikov, C.W.. (2008) GEOMICROBIOLOGY OF IRON AND ARSENIC IN ANOXIC SEDIMENTS. In Arsenic Contamination of Groundwater: Mechanism, Analysis, and Remediation pages: 123-146
Kulp, T.R., Han, S., Saltikov, C.W., Lanoil, B.D., Zargar, K., and Oremland, R.S.. (2007) Effects of Imposed Salinity Gradients on Dissimilatory Arsenate Reduction, Sulfate Reduction, and Other Microbial Processes in Sediments from Two California Soda Lakes. Applied and Environmental Microbiology. 73(16):5130-5137 (abstract)
Murphy, J.N. and Saltikov, C.W..
(2007) The cymA gene encoding a tetraheme c-type cytochrome is required for arsenate respiration in Shewanella species . J. Bacteriology. 189(6):2283-2290 (abstract)
Ahmed, M. F., Ahuja, S., Alauddin, M., Hug, S. J., Lloyd, J. R., Pfaff, A., Pichler, T., Saltikov, C.W., Stute, M., and van Geen, A.. (2006) Ensuring Safe Drinking Water in Bangladesh. Science. 314:1687-1688. (abstract)
Kulp, T.R, Hoeft, S.E., Miller, L.G., Saltikov, C.W., Murphy, J.N., Han, S., Lanoil, B. and Oremland, R.S..
(2006) Dissimilatory arsenate and sulfate reduction in sediments of two hypersaline, arsenic-rich soda lakes: Mono and Searles Lakes,
California. Applied and Environmental Microbiology. 72(10):6514-6526. (abstract)
Campbell, K.M., Malasarn, D., Saltikov, C.W., Newman, D.K., and Hering, J.G.
(2006) Simultaneous microbial reduction of iron(III) and arsenic(V) in suspensions of hydrous ferric oxide. Environ. Sci. Technol.. 40(19): 5950-5. (abstract)
Saltikov, C.W. and Malasarn, D. (2006) Arsenate-respiring prokaryotes: Manual of Environmental Microbiology 3rd edition. ASM Press.
Saltikov, C.W., Wildman, R.Jr., and Newman, D.K. (2005) Expression dynamics of arsenic respiration and detoxification in Shewanella sp. strain ANA-3. J. Bacteriology. 187:7390-7396. (abstract/paper)
Malasarn, D., Saltikov, C.W., Campbell, K.M., Santini, J.M., Hering, J. G., and Newman, D.K. (2004) arrA is a reliable marker for As(V)-respiration in the environment. Science 306(5695):455. (abstract)
Saltikov, C.W. and Newman, D.K. (2003) Genetic identification of a respiratory arsenate reductase. Proceedings of the Nation Academy of Sciences. 100:10983-10988. (abstract/paper)
Afkar, E., Lisak, J., Saltikov, C.W., Basu, P., Oremland, R., and Stolz, J. (2003) The respiratory arsenate reductase from a haloalkaliphilic bacterium Bacillus selenitireducens strain MLS10. FEMS Microbiology Letters. 226:107-112. (abstract)
Saltikov, C.W., Cifuentes, A., Venkateswaran, K., and Newman, D.K. (2003) The ars detoxification system is advantageous but not required for As(V) respiration by the genetically tractable Shewanella species, strain ANA-3. Applied and Environmental Microbiology. 69:2800-2809. (abstract/paper)
Saltikov, C.W. and Olson, B.H. (2002) Homology of E. coli R773 arsA, arsB, and arsC in arsenic resistant bacteria isolated from raw sewage and arsenic enriched creek waters. Applied and Environmental Microbiology. 68:280-288. (abstract/paper)
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