Faculty & Research
Bacterial Sporulation and Antibiotic Resistance
Antibiotic resistance has become a worldwide problem due to the misuse of readily available drugs. Moreover, the ability of bacteria to adapt rapidly to the challenge of new antibiotics gives them an advantage that cannot ever be completely overcome. It is important that we know our enemy and learn all its tactics for evading the lethal effects of antibiotics, so that we can at least win more battles than we lose. For over two decades Dr. Christine Buchanan has focused on the molecular targets of penicillin, probably the most commonly used antibiotic anywhere. The fact that there is more than one target for penicillin in the bacterial cell and that these multiple targets serve different but essential roles in bacterial growth has made this line of research significant for both medicine and basic science.
After some early work with Escherichia coli, Dr. Buchanan switched to the rod-shaped bacterium known as Bacillus subtilis. This soil organism is not itself a known pathogen but it is closely related to such medically important microbes as Staphylococcus and Streptococcus. The decision to study B. subtilis was based on the fact that it was more complex than its relatives and it could sporulate. Early in the project, Dr. Buchanan determined that there were at least seven penicillin targets in this organism; they are referred to as the penicillin-binding proteins (PBPs). Penicillin binds to these essential proteins and inactivates them. But does penicillin have to bind to all of them, to only a single one, or must a combination of the proteins be inactivated in order to kill the cell? Adding to the complexity and the excitement of the project was Dr. Buchananís discovery of a set of PBPs that is only made when the cells are sporulating. This generated a second line of inquiry into the genetic regulation of the production of the PBPs. Since her early discoveries, other labs have identified some minor additional PBPs, and completion of the Bacillus Genome Sequencing Project has generated data to suggest there are still other PBPs yet to be characterized. What does the cell do with all of them?
After performing microbial genetics and physiological studies, the Buchanan lab group published the preliminary assignment of specific functions for each of the major PBPs in B. subtilis. Subsequent biochemical and molecular biological experiments have confirmed and expanded those results. The PBPs are all enzymes involved in various aspects of bacterial cell wall synthesis. For example, one of them is an enzyme that is needed to form the septum across the cell during cell division, whereas another PBP participates only in synthesis of the sidewalls of the cell, but is not required for cell division. Three of the genes that code for PBPs were cloned and sequenced by Dr. Buchanan and her students; some of these data became part of the final report of the international Genome Sequencing Project. More recently, the lab studied medically important bacteria that produce beta-lactamases, enzymes that evolved from the PBPs. This work was done in collaboration with a member of the SMU Chemistry Department, who is designing inhibitors of these enzymes. It is interesting that a molecule can inhibit beta-lactamase activity but not the penicillin-binding activity of the proteins from which the beta-lactamase evolved. Promising compounds were examined for their antibiotic activity and their synergistic activity with conventional antibiotics.
Buchanan, Christine E., and Ann Gustafson. Mapping the gene for a major penicillin-binding protein to a genetically conserved region of the Bacillus subtilis chromosome and conservation of the protein among related species of Bacillus. J. Bacteriol. 173:1807-1809 (1991).
Ng, Clifford, Christine Buchanan, Abraham Leung, Charles Ginther, and Terrance Leighton. Suppression of defective-sporulation phenotypes by mutations in transcription factor genes of Bacillus subtilis. Biochimie 73:1163-1170 (1991).
Buchanan, Christine E., and Mei-Ling Ling. Isolation and sequence analysis of dacB, which encodes a sporulation-specific penicillin-binding protein in Bacillus subtilis. J. Bacteriol. 174: 1717-1725 (1992).
Buchanan, Christine E., and Ann Gustafson. Mutagenesis and mapping of the gene for a sporulation-specific penicillin-binding protein in Bacillus subtilis. J. Bacteriol. 174:5430-5435 (1992).
Yanouri, Ahmed, Richard A. Daniel, Jeffery Errington, and Christine E. Buchanan. Cloning and sequencing of the cell division gene pbpB, which encodes penicillin-binding protein 2B in Bacillus subtilis. J. Bacteriol. 175:7604-7615 (1993).
Daniel, Richard A., Sarah Drake, Christine E. Buchanan, Renate Scholle, and Jeffery Errington. The Bacillus subtilis spoVD gene encodes a mother-cell-specific penicillin-binding protein required for spore morphogenesis. J. Mol. Biol. 235:209-220 (1994)
Buchanan, C. E., A. O. Henriques, and P. J. Piggot. Cell wall changes during bacterial endospore formation, p. 167-186. In J.-M. Ghuysen and R. Hakenbeck (eds.), New Comprehensive Biochemistry: Bacterial Cell Wall. Elsevier Science Publishers, Amsterdam (1994)
Simpson, E. Barry, Todd W. Hancock, and Christine E. Buchanan. Transcriptional control of dacB, which encodes a major sporulation-specific penicillin-binding protein. J. Bacteriol. 176:7767-7769 (1994).
Buynak, John D., Hansong Chen, Lakshminaryana Vogeti, Venkat Rao Gadhachanda, Christine A.(sic) Buchanan, Timothy Palzkill, Robert W. Shaw, James Spencer, and Timothy R. Walsh. Penicillin-derived inhibitors that simultaneously target both metallo- and serine- beta-lactamases. Bioorg. & Med. Chem. Lett. 14:1299-1304 (2004).
Selected Papers Presented at Professional Meetings
Moss, W. E. and C. E. Buchanan. Lethal effect of limited PBP2B production in B. subtilis. Presented at the Eighth International Conference on Bacilli, Stanford Univ. (1995)
Simpson, E. B., and C. E. Buchanan. Mutagenesis of PBP 2B of Bacillus subtilis. Presented at the 9 th International Conference on Bacilli, Lausanne , Switzerland (1997).
Simpson, E. B., H. Ferris, and C. E. Buchanan. Characterization of altered forms of PBP 2B in Bacillus subtilis. Amer. Soc. Microbiol. Absts. H148, (1998).
Ferris, H. U. and C. E. Buchanan. Mutagenesis of motif #3 in the non-penicillin-binding module of PBP 2B of Bacillus subtilis. Amer. Soc. Microbiol. Absts. H200, (1999).
Simpson, E. B., H. U. Ferris, and C. E. Buchanan. Possible role for the carboxy-terminal extension of Bacillus subtilis PBP 2B. Amer. Soc. Microbiol. Absts. H201, (1999).
Simpson, E. B., H. U. Ferris, and C. E. Buchanan The third domain of Bacillus subtilis PBP 2B. Presented at the 10 th International Conference on Bacilli, Baveno , Italy (1999).
Buynak, J. D., H. Chen, L. Vogeti, V. R. Gadachanda, and C. E. Buchanan. Dual inhibitors of the metallo- and serine- beta-lactamases. Interscience Conf. on Antimicrobial Agents and Chemotherapy Absts. F344, (2002).
Current Teaching Assignments
Administrative and Service Activities at SMU (partial list)
Honors Received as SMU Faculty Member
Off-Campus Pprofessional Activities (partial list)