Anne O. SummersResearch Professor of Microbiology and Genetics
Professor Summers received a B.S. in Chemistry (1964) and an M.S. in Microbiology (1965) from the University of Illinois-Urbana. After working in technical positions at the Eli Lilly Research Laboratories (Indianapolis) and at the Institute for Molecular Virology (St. Louis University), she obtained her Ph.D. in Molecular Biology at Washington University, St. Louis (1973). She was an American Cancer Society postdoctoral fellow at the University of Virginia and a Medical Foundation Fellow at Massachusetts General Hospital before joining the Georgia faculty in 1977. She has been the recipient of an NIH Research Career Development Award (1980-85) and a Guggenheim Fellowship (1986-87).
Many metals are essential in biology as active site cofactors in metalloenzymes and as structural elements and/or inducers for key regulatory proteins in both prokaryotes and eukaryotes. However metals, such as mercury, are extremely toxic. We study the bacterial mercury resistance (mer) operon, using molecular genetics and biochemistry to elucidate the interactions of the transcriptional repressor/activator, MerR, with metals, with DNA, and with RNA polymerase. Acting at a divergent operator/promoter region, MerR represses its own transcription (regardless of whether Hg2+ is present) and it represses (without Hg2+) and activates (with Hg2+) the expression of the five mer structural genes: the three membrane-related proteins (merTPC) involved in Hg2+ uptake, the mercuric reductase (merA) which converts Hg2+ to the non-toxic, volatile Hg° form, and merD, which may have a role in regulation. The relatively small (144 aa) MerR protein does all of this from a single DNA site at which it "traps" RNA polymerase even when no inducer is present. We use a variety of genetic, biochemical and biophysical strategies to define the mechanism of activation and repression of this unusual system.
Bacterial mercury resistance is widely found in nature, and is particularly
abundant in the normal intestinal and oral flora of humans. In a
primate model system, we have demonstrated that the occurrence of Hg resistance
in the oral and intestinal flora correlates with exposure to Hg arising
from dental amalgam ("silver") fillings. We are also examining the
effect of chronic Hg exposure stress on the proliferation of multiple antibiotic
and metal-resistance plasmids in the primate.
"Phytoremediation of methylmercury pollution: merB expression in Arabidopsis thaliana confers resistance to organomercurials," Bizily, Scott P.; Rugh, Clayton L.; Summers, Anne O.; Meagher, Richard B. Proc. Natl. Acad. Sci. 1999, 96, 6808-6813.
"Cd(II)-responsive and constitutive mutants implicate a novel domain in MerR," Caguiat, Jonathan J.; Watson, Alice L.; Summers, Anne O. J. Bacteriol. 1999, 181, 3462-3471.
"The core metal-recognition domain of MerR," Zeng, Qiandong; Stalhandske, Christina; Anderson, Meredith C.; Scott, Robert A.; Summers, Anne O. Biochemistry 1998, 37, 15885-15895.
"Bacterial oxidation of mercury metal vapor, Hg(O)," Smith, T.; Pitts, K.; McGarvey, J.; Summers, A.O. Appl. Environ. Microbiol. 1998, 64, 1328-1332.
"Population biology of the mercury resistance (mer) operon in the facultative Gram negative enteric flora of humans and other primates," Wireman, J.; Liebert, C.A.; Smith, T.; Summers, A.O. Appl. Environ. Microbiol. 1997, 63, 4494-4503.
"A rubrerythrin operon and nigerythrin gene in Desulfovibrio vulgaris (Hildenborough)," Lumppio, H. L.; Shenvi, N. V.; Garg, R. P.; Summers, A. O.; Kurtz, D. M., Jr. J. Bacteriol. 1997, 179, 4607-4615.
"Near-zero background cloning of a PCR product," Zeng, Q.; Eidsness, M. K.; Summers, A. O. BioTechniques 1997, 23, 412-418.
"A glutamate regulatory protein (Grp) in Escherichia coli?" Zeng, Q.; Summers, A. O. Molec. Microbiol.1997, 24, 231-232.
"Mutations in the alpha and sigma-70 subunits of RNA polymerase affect expression of the mer operon," Caslake, L. F.; Ashraf, S. I.; Summers, A. O. J. Bacteriol. 1997, 179, 1787-1795.
"Phylogeny of mercury resistance (mer) operons of Gram negative bacteria isolated from the fecal flora of primates," Liebert, C. A.; Wireman, J.; Smith, T.; Summers, A. O. Appl. Environ. Microbiol. 1997, 63, 1066-1067.
Mercuric ion reduction and resistance in transgenic Arabidopsis thaliana plants expressing a modified bacterial merA gene," Wilde, D.; Stack, N.; Rugh, C.; Thompson, D.; Summers, A. O., Azarraga, L.; Meagher, R. B. Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 3182-3187.