Wehr Life Sciences, 208
M.S., 1987, Sofia University "St. Kliment Ohridski" , Bulgaria
Ph.D., 1994, Sofia University "St. Kliment Ohridski", Bulgaria
Post-doctoral Training, University of Illinois at Urbana-Champaign, IL
Research Associate Microbiologist, University of California at Davis, CA
Work in my laboratory is based on key concepts and emerging trends in molecular and environmental microbiology to support research and application development in biodegradation of pollutants, nanobiosensors, and biotechnology.
Contaminated environments are unfortunately part of our modern landscapes. Fuels oxygenates, in particular methyl tertiary butyl ether (MTBE) are often associated with gasoline spills and have formed long plumes in groundwater. MTBE is a primary groundwater contaminant in the US and its downstream metabolite, tert-butyl alcohol (TBA), is a potential carcinogen. In studies of MTBE biodegradation in situ, my group has linked for the first time the presence of “native” Methylibium petroleiphilum PM1-like bacteria with MTBE degradation activity in numerous places in the US using technologies such as real-time qPCR, cloning/sequencing, and luminescent lanthanide nanoparticles-based assays. To determine the role of key enzymes in aerobic MTBE degradation, we have applied whole genome expression analyses and developed new genetic system based on homologous recombination for strain PM1. We proved that the protein product MdpA is responsible for MTBE conversion to hydroxy-MTBE, while the enzyme complex MdpJ/K is involved in TBA hydroxylation to hydroxy-methyl propanol. Currently we are working on understanding the genetic regulation of MTBE pathway and on the expression, biochemical characterization, and crystal structure of MdpJ/K proteins.
In today’s modern world the increased production and use of nanomaterials in products such as make-up, sunscreen, stain-resistant clothing, paint, pesticides is very common. Because of, the disposal of such products and the amount of possible environmental contamination, the effects of these nanoparticles on native ecosystems is of particular interest. A project in the lab is attempting to determine the ecotoxicity of nanoparticle exposure in the natural environment by the use of microcosms containing several species of plants, a natural microbial community, and other organisms commonly found within soil. Through the use of molecular tools such as RT-qPCR, micro-arrays, and RAPD analysis we will monitor the potential changes of the soil ecosystem brought about via nanoparticle exposure.
Development of biosensors for environmental diagnostics and monitoring is another important research area in my lab. Sensitive, effective means of environmental monitoring are vital to ecosystem protection, including the identification of environmental hazards and the effects of toxic substances and nutrients. In our approach current chip-based microarrays are replaced with a nanoparticle-based technology by shifting the immobilized probe DNA from the chip surface to a NP surface and performing hybridization in solution with target DNA (collaboration with colleagues from Dept. Mechanical Engineering, UCD).
We have already demonstrated the advantage of such a nanotechnology for detection of MTBE-degrading bacteria, antibiotic resistance genes and for detection of single nucleotide DNA mutations. Presently we are working on developing whole-cell based and protein-based biosensors to support field measurements.
The lab is also involved in studying microbial community structure and function in the Deep-water Horizon oil spill in the Gulf of Mexico. To characterize the biodegradation ability of the community microcosm lab incubations are combined with functional microarrays and qPCR analyses.
Other project involves work to optimize and implement an economic and sustainable method for in situ removal of waterborne Se at a pilot agricultural drainage water treatment facility. Objectives include (a) uptake of Se by brine shrimp followed by their harvesting, and volatilization of Se by microalgae; (b) production of economically valuable by-products from the process such as food supplements, biofuel production, and CO2 sequestration. This project is in collaboration with scientists from CA Department of Water Resources, USDA, and Biodiesel Industries Inc.
Nozawa-Inoue, M., Jien, M., Yang, K., Rolston, D.E., Hristova, K.R., and Scow, K.M. 2011. Effect of nitrate and electron donors on native perchlorate-reducing microbial communities and their activity in vadose soil. FEMS Microbiol. Ecology. 76:278-288.
Shi, J.Y., Abid, A.D., Kennedy, I.M., Hristova, K.R., and Silk, W.K. 2011. To duckweeds (Landoltia punctata), nanoparticulate CuO is more inhibitory than the soluble copper in the bulk solution. Environmental Pollution. 159: 1277-1282.
Chan, M.-L., Jaramillo, J., Hristova, K.R., and Horsley, D.A. 2011. Magnetic scanometric DNA microarray detection of methyl tertiary butyl ether degrading bacteria for environmental monitoring. biosensors and bioelectronics. 26:2060-2066.
Yang, J., Rasa E., Prapakorn T., Scow K., Yuan H., and Hristova K.R. 2010. Mathematical model of Chlorella minutissima UTEX2341 growth and lipid production under photoheterotrophic fermentation conditions. Bioresource Technologies. 102: 3077-3082.
Son, A., Kennedy, I.M., Scow, K., and Hristova, K.R. 2010. Quantitative gene monitoring of microbial tetracycline resistance using magnetic luminescent nanoparticles. J. Environ. Monitoring, 12: 1362–1367.
Schmidt, R., Battaglia, V., Scow K., Kane, S., and Hristova, K.R. 2008. A novel enzyme, MdpA, is involved in MTBE degradation in Methylibium petroleiphilum PM1. Appl. Env. Microbiol. 74: 6631-6638.
Hristova, K.R., Schmidt, R., Chakicherla, A., Legler, T., Wu, J., Chain, P., Scow, K.M., and Kane, S. 2007. Comparative transcriptome analysis of Methylibium petroleiphilum PM1 exposed to the fuel-oxygenates methyl-tert-butyl ether and ethanol. Appl. Env. Microbiol, 73: 7347-7357.
Way Klingler Young Scholars Award (2013)
Michael Mashock (Ph.D. student)
Nadia Hallaj (undergraduate)
Neha Ahuja (undergraduate)
Dr. Hristova is currently accepting new Ph.D. students
Geetika Joshi, Tee Prapakorn, Reef Holland (Soil Sci. 2011), Jennifer Bradford (AgEnv. Chem. 2008), Adriana Ortegon (Soil Sci. 2008), Kristin Hicks (Soi Sci. 2007), Vincent Battaglia (Soil Sci. 2006), Stephanie Smith (AgEnv. Chem. 2005), Banu Inceoglu (AgEnv. Chem. 2004).