Karsten R.O. Hazlett, PhD

This lab engages a multifaceted approach toward analyzing the physiology and pathogenesis of the bacterial pathogens Treponema pallidum and Treponema denticola, the causative agents of syphilis and periodontal disease respectively. Despite the high global incidence of treponemal infection (~12 million new cases of syphilis/year, ~30% of adults have periodontitis), there are currently no vaccines for these human pathogens. The ultimate goal of our efforts is the identification of prophylactic and/or therapeutic targets for syphilis and periodontal disease. While immunity to extracellular microbes is varied and complex, all current bacterial vaccines are based upon components of the pathogen's surface. Largely, this is due to the accessibility of these surface antigens to vaccine-induced host antibodies which, upon binding to the bacterium, may effect killing through complement deposition, phagocytosis, and/or direct bactericidal activity. Because protein antigens are able to stimulate immunological memory and affinity-maturation of antibodies, bacterial outer surface proteins are ostensibly the best candidates for vaccine development. A principal goal of this lab is the identification of outer membrane proteins (OMPs) of the pathogenic spirochetes T. pallidum and T. denticola. The pursuit of a T. pallidum OMP has been hindered for the last quarter century because the bacterium cannot be cultivated in vitro, is genetically intractable, and has a protein-poor outer membrane which is fragile enough to be breached by common surface labeling techniques. To circumvent these obstacles we employ a battery of bio-informatics/genomics, molecular, biochemical/biophysical, and immunological techniques to identify and characterize candidate proteins. Although this multi-pronged approach recently led to the identification of the first bona-fide T. pallidum OMP (Hazlett. 2005. J. Bac), our search remains active as this highly-atypical OMP lacks surface exposure and, accordingly, offers no protection as a syphilis vaccine. To augment our technical armamentarium and to expand the scope of our research program, we have begun a series of studies on the cultivatable, genetically-manipulable oral treponeme T. denticola. In addition to providing a cultivatable platform for the heterologus expression of T. pallidum genes, it is anticipated that these efforts will lead to the identification of T. denticola OMPs as vaccine candidates for periodontitis. Additionally, as ~70% of T. pallidum genes are reasonably well-conserved in T. denticola, this tact may also provide clues in our continuing quest for T. pallidum OMPs. A second area of interest in this lab, trace-metal and oxidant homeostasis, has relevance to both treponemal physiology and pathogenesis. Scavenging of sequestered host iron and the role of bacterial antioxidant enzymes are established paradigms of contemporary bacterial pathogenesis. However, treponemes have a reduced iron requirement (most pronounced in T. pallidum) and lack the classical antioxidant enzymes superoxide dismutase and catalse. We and others have made significant initial strides by characterizing the structure, function, and regulation of i) the Tro metal-uptake system (Hazlett. 2003. JBC, Lee. 2002. J. Bac.) and ii) a novel antioxidant enzyme, neelaredoxin (a superoxide reductase; Jovanovic. 2000. JBC). However, many aspects of the treponemal antioxidant and metal-homeostasis pathways remain to be elucidated. By unraveling these facets of the treponemes unorthodox physiology, we anticipate gaining further insights into the pathogenic method of these usual bacteria and, potentially, uncovering novel targets for the development of antimicrobial agents.