Research - Category II: Aquatic Ecosystems

Assessing the Response of Degradative Biofilms to Groundwater Pollutants
(Funded 2000-2001)

Principal Investigators:
Jay Keasling
Department of Chemical Engineering
UC Berkeley
(510) 642-4862
keasling@socrates.berkeley.edu

Eric Gilbert
Department of Chemical Engineering
UC Berkeley
(510) 643-1876
gilbert7@socrates.berkeley.edu

Executive Summary:
Bacteria play an important role in the detoxification of polluted groundwater. At sites where intrinsic bioremediation is employed, the clean-up subsurface contaminants is dependent on the catalytic abilities of indigenous microorganisms. Alternatively, direct application of specific degrader microorganisms to enhance in situ biodegradation is under consideration for treatment of several recalcitrant groundwater pollutants, including MTBE. In recent years there has been a growing appreciation among microbial ecologists that most bacteria in the environment live in communities of microorganisms attached to surfaces, or biofilms (Characklis and Marshall, 1990; Costerton, 1999). Moreover, it has been recognized that the metabolism of complex organic pollutants often involves the concerted efforts of multi-species bacterial consortia (Field et al., 1995; Vanginkel, 1996). This shift in our understanding of the structure and function of microbial communities could impact the methods that are used to treat these contaminants and the models that predict rates of groundwater decontamination. hence, there is a need to understand the interactions between contaminants and bacteria in biofilms and new parameters that more accurately describe the contaminant-bacterial interactions must be defined.

This study will delineate the capacity of biofilms to respond to changes in toxicant concentration. Several factors are expected to influence the nature of the response. Inputs of contaminants to groundwater will be stochastic; for example, resulting from occasional pesticide applications or following seasonal rainfall. Additionally, the ability of a biofilm to break down a contaminant will frequently be a concentration-dependent function. Adaptation of a biofilm to changes in toxicant concentrations will also depend on the interactions among the community members involved in detoxification of the contaminant. To help evaluate the importance of these variables, we have developed both a computer simulation and laboratory tools that allow one to observe interactions between bacteria and between bacteria and contaminants in a biofilm. Several model microbial consortia have been assembled to facilitate the study of ecological interactions in biofilms, including a two-member co-culture that mineralizes the herbicide and groundwater contaminant atrazine.

The expected benefits of this research are an improved understanding of the interactions of groundwater contaminants with degradative biofilms. This information is relevant to modeling the fate of groundwater contaminants, and could contribute to reduced toxicant exposure for populations obtaining their drinking water from subsurface water supplies.