Over the years, my research has focused on various aspects of microbiology. Most recently, students have studied four topics: the actinorhizal symbiosis, cheese microbiology, tick symbionts and the biochemistry of psychrophilic bacteria. The unifying theme behind these areas is the interaction of microorganisms with their environment, whether it be in plants, in animals, in food or at temperature extremes.
Our current focus is on the nitrogen-fixing symbiosis between actinomycetes from the genus Frankia and angiosperms. A tour of the symbiosis can be found at the Frankia website that was assembled using funds from the NSF-USDA Joint Microbial Genome Sequencing program. Our current efforts are directed at understanding the overall structure and characteristics of the Frankia genome compared to closely related organisms. We are attempting to tease out the genes that make Frankia unique and that enable the organism to enter into a symbiosis with higher plants. (top)
We have had an interest in traditional cheese ripening as viewed from the perspective of microbial ecology. Populations in ripening cheese appear and diminish according to a predictable pattern and depending on the natural environment, the milk source and the treatment accorded the curds prior to ripening. We have studied the microbial diversity of the ripening process as a whole and viewed the molecular diversity of Geotrichum candidum one of the early inhabits of ripening cheese, in its natural habitats in the cheese caves of France. See the following articles for more information (top): Appl. Environ. Microbiol. 67:4752-4759; Appl. Environ. Microbiol. 58:3448-3454.
One of the students in the lab, Jeffrey Gawronski, now at the University of Massachusetts Medical School, investigated the molecular adaptation of enzymes to cold temperatures. To do so, he cloned, sequenced and expressed the gene for glutamine synthetase (glnA) from a series of marineMoritella sp. and related bacteria that had temperature optima for growth from around 5 C up to 40 C. He purified the cloned enzymes from E. coli and determined their kinetic parameters, heat stabilities and other biochemical behaviors. Despite being highly conserved, a fewamino acid substitutions allowed for the cold-adapted enzymes to have catalytic efficiencies at the same level as warm-adapted enzymes when assayed at the optimum temperature for growth of the producing organism. Evolution into cold environments can thus occur by one or a few amino acid changes that affect the kinetic constants of the enzymes being modified followed by minor optimizations, rather than many changes that would have to have occured simultaneously.
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