SPRING SEMINAR SERIES

"Interplay between fermentation and respiration in

the sulfate-reducing bacteria"

Judy D. Wall Professor of Biochemistry

University of Missouri

Anaerobes are thought to be dependent on fermentation. New information about the strictly anaerobic, sulfate-reducing bacteria of the genus Desulfovibrio cast some doubt on their dependence on fermentative pathways. These bacteria are the focus of our efforts to determine the wiring diagram for electron flow to electron acceptors including protons for hydrogen generation. With the organic acids, lactate, pyruvate or fumarate, these bacteria produce a series of reduced end products among them being small amounts of hydrogen. Analysis of a mutant lacking the type-1 tetraheme cytochrome c3 in D. desulfuricans G20 has revealed that this mutant does not reduce sulfate with pyruvate as electron donor. From this observation, we infer that electrons from pyruvate must traverse the cytoplasmic membrane twice, once to reach the cytochrome and a second time to return to the adenylylsulfate reductase responsible for sulfate reduction. Apparently unlike pyruvate, electrons from lactate bypass that cytochrome and reach sulfate, although a greater share of electrons are diverted to hydrogen. Curiously, the mutant lacking the cytochrome c3 also grows more robustly on pyruvate without sulfate than does the parental strain. Analyses of accumulated end products indicate potential pathways operating during these growth modes and show that respiration and fermentation are occurring simultaneously rather than being mutually exclusive. Microarray and proteomic analyses of the expressed genes and proteins differentially expressed in the parental and mutant strains growing with sulfate or with pyruvate alone are in remarkable agreement regarding the enzyme systems responsible for some of these changes in growth. In addition, assays of mutants with transposon insertions in the genes identified are being used to confirm the pathways. Models consistent with the observations of electron flow will be presented.

3:30- 4:30pm Thursday, April 8, 2010

239 Gortner Lab St. Paul Campus

Questions or special needs please contact Marie Raley at 612.624.6774 or bti@umn.edu