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Madigan, Michael T.

Dr. Michael T. Madigan

Department of Microbiology
Southern Illinois University
Carbondale, IL

Bacterial Diversity
The main research theme in my laboratory is the isolation and characterization of new species of anoxygenic phototrophic bacteria (anoxyphototrophs) from extreme environments, in particular thermal, permanently cold, or extremely alkaline and hypersaline habitats. The long term objective is to better understand the physiochemical limits to and evolution of photosynthesis. We are interested in the physiology, phylogeny, pigments and other basic biological properties of extremophilic anoxyphoto-trophs that combine to allow these organisms to grow optimally under one or more physical or chemical extreme. Our work also contributes to an understanding of the evolution of phototrophic microorganisms since extreme environments are models of early earth conditions. Some of our work involves collaborations with biophysicists, biochemists, and geneticists interested in particular aspects of the biology of extremophilic phototrophs.

Some of the organisms we have characterized include the thermo-philic purple sulfur and green sulfur bacteria Chromatium tepidum and Chlorobium tepidum, respectively, and the phylogenetically unique thermophilic phototroph Heliobacterium modesticaldum. These organisms have been isolated from various thermal springs in Yellowstone National Park (USA), New Zealand, and Iceland. Other extremophilic anoxyphototrophs studied in this laboratory include psychrophilic organisms from Antarctica, extremely halophilic organisms from the Dead Sea, and alkaliphilic phototrophs from various highly alkaline soda lakes in the western United States and in Northern Africa.

In a collaboration with the laboratory of Robert Kranz, Washington University, St. Louis, we are also interested in the production of biopolymers by anoxyphototrophs. Several prokaryotes produce lipid storage materials called poly-beta-hydroxyalkanoates (PHAs), the most common being poly-beta-hydroxybutyrate (PHB). Anoxyphototrophs make large amounts of PHAs under certain growth conditions and a variety of PHAs are known in which the butyrate moiety is substituted by some other hydroxyalkanoate. These completely biodegradable polymeric materials have interesting chemical and physical properties and some have been identified as potential plastic substitutes. We are studying the chemical diversity of these biopolymers produced by various anoxyphototrophs and are involved in a detailed study of the physiology and genetics of PHA production in the anoxyphototroph Rhodobacter capsulatus. s A long range goal of this research would be to use an anoxyphototroph such as R. capsulatus as a photo biological production system for the commercial production of PHAs.