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4:00 p.m.
Slip Sliding Away and Getting a Tan: A Tale of Two Bacteria and How They Respond to Physical Changes in Their Environment

Abstract: Bacteria live in complex communities where chemical and physical factors and the microbial census can change rapidly. As a result, bacteria often need to adapt quickly to environmental change. Over the past several years, our lab group has been investigating how two different species of bacteria respond to biochemical and physical alterations in their environment. Bacillus cereus is a common soil-dwelling bacterium that may cause gastrointestinal disease when consumed in unpasteurized dairy products. When grown on solidified nutrient-rich media, these bacteria exhibit swarming, a type of high-energy motility facilitated by the hyperproduction of flagella. On media containing cow’s milk, however, B. cereus exhibits sliding motility, characterized by elaborate dendritic outgrowths from the central mass of the colony. Recent work in our laboratory has shown that the major milk protein casein alone can induce B. cereus sliding. Casein is a hydrophobic protein, so we hypothesized that other agents that alter the hydrophobicity or surface tension of the agar would have a similar effect. When grown on media containing the nonionic detergent NP-40, B. cereus also exhibited sliding. This suggests that the bacteria are sensing a physical change in their environment leading to a switch in their mode of motility. We have recently isolated a collection of mutants that do not slide on milk or NP-40, and are using molecular genetic techniques to clone and sequence the affected genes. The second microbe we study is a novel bacterium isolated by students in our lab, which we have named Pseudomonas uticensis. Among the interesting attributes of this bacterium is that it produces the brown pigment melanin. Studies in our lab revealed that melanin production is regulated by light; bacteria grown in the dark are unpigmented but turn brown within hours of exposure to white light. Exposure to increasing light intensity enhances melanin production, suggesting that the bacteria have a photosensory mechanism that regulates pigment production. Recently, we have also discovered that melanin production increases proportionately with increased cell density in culture. This suggests that quorum sensing signaling pathways also regulate melanin production in P. uticensis. We have isolated several mutant strains of the bacterium that are defective in melanogenesis, as well as one mutant strain that overproduces melanin, and are working to identify the genes involved in light- and quorum-regulation of melanin production in P. uticensis. The Asa Gray Seminar Series is sponsored by the Asa Gray Biological Society, and is the longest running seminar series at Utica College. Scientists are invited from throughout the region to present seminars on their ongoing research. All lectures are held in Donahue Auditorium, Gordon Science Center, at 4:00 p.m. An informal reception immediately follows. Call (315) 792-3028 for more information.