Superfund Research Program
Chemical Mapping of Chromate Uptake, Localization, and Reduction in Remediating Bacteria
Project Leader: Joseph MK Irudayaraj
Grant Number: R01ES017066
Funding Period: 2009-2011
In the United States, chromate is the third most common contaminant of hazardous waste sites and the second most common inorganic contaminant found in the environment. In situ and ex situ bioremediation processes that exploit the intrinsic metabolic capabilities of dissimilatory metal ion-reducing bacteria (DMRB) remain potent, potentially cost-effective approaches to the reductive immobilization or detoxification of environmental contaminants. Despite several advances made in elucidating Shewanella biology as it relates to chromate transformation, fundamental questions about the specific chromate reduction mechanism remain unclear. This information gap includes:
- the identity of dedicated chromate reductase(s),
- the cellular localization of chromate transformation (e.g., distal appendages, outer cell surface, periplasm, cytoplasmic membrane, cytosol), and
- the environmental parameters under which microbial populations have the greatest specific chromate reduction rates.
The problem in predicting and assessing bioremediation performance is compounded by the lack of fundamental knowledge of the molecular basis, regulatory mechanisms, and biochemistry enabling bacterial metal-reducing capabilities. The overarching hypothesis of Dr. Irudayaraj's research is that chromate-functionalized, surface-enhanced Raman active gold nanostructures and intracellularly grown gold nanoislands can serve as ultrasensitive probes for Raman chemical mapping for delineating cellular localization of Cr(VI) reduction and environmental factors impacting rates of Cr(VI) reduction.
The researchers show that chromate decorated gold nanoparticles and intracellularly grown gold nanoslands are nontoxic and can be used as beacons to reveal the intracellular chromate [chromium (VI)] reduction sites and localization of Cr(III) in single cells of the environmentally important metal-reducing bacterium Shewanella oneidensis MR-1. They show that Raman spectroscopy has the potential to distinguish multiple metallic or species and thus can be incorporated to probe multiple metal reduction reactions in single as well as in communities of organisms. They confirm the Raman maps with 3-dimensional Fluorescence Lifetime imaging (FLIM) using YFP labeled S. oneidensis MR-1. The reserachers expect their findings to provide insights into the characteristics of active bacteria contributing to the reduction so that effective remediation measures can be taken.