McMahon Lab:Research

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Microbial Ecology & Environmental Engineering

Microbes possess extraordinarily diverse and sophisticated physiologies, communication strategies, and mechanisms of evolution. Scientists and engineers are only beginning to understand and exploit the metabolic potential of these organisms and their communities. The broad objective of our research program is to improve our capacity to predict and model microbial behavior, while searching for novel biologically mediated transformations that can be harnessed for engineering applications.

The McMahon Lab studies the microbial ecology of natural and engineered systems, with an emphasis on those that use microbes to remove pollutants from water. We use molecular tools to investigate microbial community structure and function in activated sludge and freshwater bodies. This information will ultimately lead to the construction of better mechanistic models to describe such processes as wastewater treatment, bioremediation, and nutrient cycling.

We also seek to understand the population ecology of microorganisms relevant to our environmental systems. Horizontal gene transfer and recombination are important mechanisms of microbial evolution. The extent to which genes are horizontally transferred between species of microbes will partially determine how populations respond to the chemicals they are exposed to in the environment. This has important implications for the capacity of microbial communities to remediate many different kinds of pollutants.

Enhanced Biological Phosphorus Removal

Enhanced Biological Phosphorus Removal (EBPR) is used worldwide to remove phosphorus from both municipal and industrial wastewaters, protecting our surface waters from excessive algal growth and the associated long-term degradation of water quality. Despite its successful use, very little is known about the naturally occurring microorganisms that carry out EBPR. These microorganisms have eluded researchers for over 30 years – they cannot be grown in pure culture. One major group of EBPR organisms was recently identified by cultivation-independent techniques and was named Accumulibacter phosphatis. The goal of this research is to learn more about the mechanism responsible for EBPR and the ecology of Accumulibacter.

Community and population ecology of Accumulibacter - We have identified at least five different species-like groups of Accumulibacter in lab and full-scale EBPR systems. The relative abundance of these different groups can be determined using a real-time quantitative PCR technique we have developed to target the polyphosphate kinase gene. This genetic marker allows for detection of individual groups for comparative purposes across time and space. We are currently investigating the ecology of these species-like groups to determine if their differences account for varying performance in full-scale EBPR systems. We also were recently awarded up to twelve 454-FLX (pyrosequencing) runs to explore community and population dynamics in EBPR communities, through the Joint Genome Institute.