Q-207. Multigene Analysis to Elucidate Organisms Involved in Cr Bioreduction

M. Hadi1, R. Chakraborty2, Y. Light2, J. L. Fortney2, R. Meagher2, A. P. Arkin2, T. C. Hazen2, A. K. Singh1;
1Sandia Natl. Lab., Livermore, CA, 2Lawrence Berkeley Natl. Lab., Berkeley, CA.

In any given microbial ecosystem, 99% of bacteria resist cultivation and can’t be analyzed with traditional high throughput techniques. Metagenomic analysis and dynamics of microbial communities can be gleamed using digital PCR techniques and single cell comparisons. In situ bioremediation using indigenous microorganisms is one of the many techniques that has shown promising results in recent years. Although indigenous bacteria at the site can degrade/sequester a wide range of hazardous compounds however, the bacterial population and decontamination efficiency can be affected by high concentrations of toxic compounds (e.g. heavy metals etc). Furthermore, current molecular techniques do not exist to identify the predominant contributor specie(s) and the mechanism of detoxification/sequestration. Recently a hydrogen release compound (HRC) stimulation field test was preformed to investigate bioreduction of Cr(VI) to Cr (III) at Hanford (site 100H). Post injection of the HRC, the Cr(VI) levels drastically decreased. Microarray analysis identified four key bacterial species that could be the major contributors to this bioreduction process. Based on the microarray results, several anaerobic enrichments were initiated in defined media, and 3 strains were isolated that were very closely related to Desulfovibrio vulgaris, Geobacter metallireducens and Pseudomonas stutzeri spp. When individually tested in the lab, all the isolates were capable of Cr(VI) reduction. However to elucidate the contribution of these organisms to the Cr(VI) reduction process in-situ, we attempted a mesocosm study and monitored the stoichiometry of bacterial population and the expression of several key enzymes reported to be involved in Cr(VI) reduction using digital PCR as a function of the Cr(IV) depletion. This is a novel technique not commonly used for bioremediation studies. We discuss our results and present a preliminary model for Cr(IV) bioreduction in this complex environment. We also outline some future detection strategies for similar studies.