Emeritus Office
4544A Gardner Hall
Campus Box 7615
North Carolina State University
Raleigh, NC 27695
919.515. 3770 (voice)
919.515.7867 (fax)
paul_bishop@ncsu.edu
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Paul E. Bishop
USDA Professor of Microbiology
Alternative nitrogen fixation systems in Azotobacter vinelandii
Research Brief
In 1980 we reported evidence for the presence of an alternative N2 fixation system in the soil bacterium Azotobacter vinelandii which is expressed in the absence of molybdenum. Since molybdenum has long been thought to be essential for nitrogen fixation, this was a rather startling finding. Since that time nifHDK (structural genes encoding the conventional molybdenum-containing nitrogenase) deletion strains have been used to provide definitive evidence for the existence of two alternative nitrogen fixation systems in A. vinelandii. One of the alternative nitrogenases is a vanadium-containing enzyme complex while the other appears to be devoid of both vanadium and molybdenum. We have concentrated our efforts on the latter enzyme system since this nitrogenase may ultimately provide the best means to a more complete understanding of how nitrogenases catalyze the reduction of N2 to NH4+. Our ultimate objectives are to understand the mechanism of N2 reduction by this new nitrogenase and both the genetic organization and regulation of this system and of the vanadium nitrogenase system. We have cloned, sequenced and mutagenized the genes encoding the nitrogenase structural proteins for both alternative nitrogenases as well as many of the auxiliary genes involved in these nitrogenase systems. We have also purified and partially characterized the non-molybdenum and non-vanadium nitrogenase. Our most recent efforts have been aimed at an indepth study of the regulation of the alternative nitrogenase systems using lac fusions and Northern blot analysis to study the regulation of transcription by molybdenum and vanadium. Finally, we would like to begin to ask questions about the distribution of alternative N2 fixation systems in other bacteria (besides A. vinelandii) and the importance of these systems to the global nitrogen cycle. Recent findings indicate that at least three different species of phototrophic bacteria contain alternative nitrogenases of the non-molybdenum and non-vanadium type.
Biographical Sketch
Paul Bishop was born in Portland (Oregon) and spent most of his childhood in Coupeville, Washington (on Whidbey Island) where he spent his summers working on farms. Since Paul's parents were trained in science he was exposed to science since early childhood. Paul did his undergraduate work at Washington State University where he obtained a B.S. degree with an emphasis on biology and chemistry. During his last two years as an undergraduate Paul worked part time doing synthetic organic chemistry with derivatives of cholesterol and he also worked for a short period in a laboratory doing research with vitamin B6. Upon graduation, Paul joined the Peace Corps and spent two years in a small village in Panama as a "grass roots" agricultural extension agent. Paul then spent a year working as a technician in a laboratory doing research on retinal metabolism at the University of Washington, before attending Oregon State University as a graduate student. He spent a year in the Department of Microbiology and then transferred to the Department of Food Science where he studied the effect of aflatoxin B1 on the bacterium Bacillus megaterium. Paul obtained his M.S. and then continued his Ph.D. studies working on the isolation and characterization of mutants of Bacillus subtilis resistant to aflatoxin B1 and ethidium bromide. Paul remained for two years at Oregon State University to do postdoctoral research in the field of nitrogen fixation, and followed this with another two-year postdoctoral stint at the University of Wisconsin (Madison) working on the genetics of nitrogen fixation in the soil bacterium Azotobacter vinelandii. In the spring of 1977 Paul took a position with the Agricultural Research Service of the U.S. Department of Agriculture (USDA/ARS) located in the Department of Microbiology, North Carolina State University. Since that time Paul's federally funded research program has focused on alternative molybdenum-independent nitrogenase systems, which were discovered in his laboratory in 1978-80. He also spent a sabbatical year at the AFRC Unit of Nitrogen Fixation located at the University of Sussex (England). Paul remains in the Department of Microbiology as a research microbiologist with USDA/ARS and he also holds the academic rank of Professor of Microbiology.
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