SGER: Metabolic Responses to Xenobiotic Chemical Stressors in Microbial Systems

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0302432 Peters There are numerous examples of engineered and natural systems in which the functioning of the system relies on a stable biological community of microorganisms. An excellent example is the activated sludge in an engineered biological treatment system. Perturbation of such systems by xenobiotic chemicals may lead to biological stress and subsequent shifts in the structure and function of the microbial community. Changes manifested at the population level may include diversion of resources away from growth processes, and physiological or evolutionary adaptation of the species. Changes at the community level may include shifts in species diversity, shifts in catabolic function, and alteration of the overall stress tolerance of the community. The key to understanding the link between cellular-level responses to chemical stressors and population- and community-level responses lies in the metabolic responses of individual species. This project seeks to (i) establish methodologies to measure metabolic responses to chemical stressors, and (ii) test a critical hypothesis regarding growth kinetic responses to chemical stressors. Recent work has shown that oxidative chemical stressors evoke the glutathione-gated potassium efflux GGKE) stress response in Gram negative bacteria. This mechanism is expected to impose energy requirements beyond those normally required for cell maintenance and growth. It is hypothesized that this response will manifest itself at the population level as a reduction in growth for a given substrate utilization rate, i.e. a reduction in the apparent biomass yield coefficient. Experimental systems will involve Pseudomonas stutzeri GM-1 as a target organism and two model chemical stressors, benzene and N-ethylmalemide (NEM). Measurements of biomass growth, substrate utilization and oxygen uptake will be interpreted using mathematical models to infer the extent to which the chemical stressor places excess carbon and energy requirements on the metabolic functions. A second type of experiment will explore the ability of a population to adapt to chemical stressors thereby tolerating ongoing perturbations. Broader Impacts:The primary educational component of this project is in the form of senior thesis topics envisioned to be computational rather than experimental. These projects would involve mathematical modeling to explore shifts in community structure and their relation to cellular- and population-level stress response mechanisms. This year-long SGER project will test new hypotheses and generate findings that are critical to the further development of new research in microbial stress responses. Further knowledge gained in this research area will lead to broad insights about microbiological stress response mechanisms and their manifestations at a variety of organizational scales. This information can ultimately be useful in more accurate ecological risk assessments, effective design and operation of biotreatment systems, and development of molecular biosensors for detecting chemical stressors.