Professor

Professor; Ph.D., UCLA, 1971.
Physiology of photosynthetic bacteria; mode of action of herbicides on photosynthetic bacteria and soil microbial populations.

T

he primary focus of my research has been the mode of action of certain herbicides on photosynthetic bacteria and on soil bacteria. For the photosynthetic bacteria, I have characterized the mechanism for how atrazine and other s-triazines inhibit p hotosynthetic electron transport in the purple nonsulfur bacteria and how resistance to these inhibitors develops in this group of organisms. The s-triazines act as quinone antagonists whereby they replace ubiquinone on a binding site associated wi th the L-subunit of the photosynthetic reaction center. Resistance to these herbicides occurs when a mutation in the L-subunit gene gives rise to an amino acid change in the binding protein thereby diminishing the affinity of the herbicide for the quinone binding site. Studies in my lab have also shown that atrazine induces the production of stress proteins in herbicide-sensitive strains of these bacteria. More recently, the research focus has shifted to another class of herbicides, the sulfonylureas, whi ch inhibit the enzyme acetolactacte synthase(ALS), the first enzyme in the biosynthetic pathway for valine/isoleucine. This work has concentrated on soil bacteria that are resistant to the sulfonylureas and a characterization of ALS in these bacteria. Th us far, investigations have shown that the ALS in the soil isolates and in photosynthetic bacteria is different in its response to these herbicides when compared to the model system described for Escherichia coli.

Selected Publications:

Brown, A.E., C.T. Highfill, and B. Truelove. 1994. The production of polypeptides by s-triazine treated Rhodobacter sphaeroides. Microbial Releases. 2:281-288.

Brown, A.E., R. Luttrell, C.T. Highfill, and A. Rushing. 1990. Characterization of naturally occurring atrazine-resistant isolates of the purple nonsulfur bacteria. Applied and Environmental Microbiology 56:507-513.

Brown, A.E., B. Truelove, C.T. Highfill, and S. Smith. 1988. Physiological competence of atrazine-resistant strains of the photosynthetic bacterium Rhodobacter sphaeroides (Rhodospirillaceae). Weed Science 36:703-706.

Brown, A.E., C.W. Gilbert, R. Guy, and C.J. Arntzen. 1984. Triazine herbicide resistance in the photosynthetic bacterium Rhodopreudomonas sphaeroides. Proc. Nat. Acad. Sci. USA. 81:6310-6314.

Courses Taught:

MB 300 General Microbiology

MB 302 Medical Microbiology

MB 400 Methods in Microbiology

MB 460 Special Problems

MB 541 Applied and Environmental Microbiology

MB 558 Photosynthesis

MB 609 Biomembranes