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.
Dr. Madigan is an author on these YNP topic Publications: