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Our lab has research in the Gram-positive genus Streptomyces
and the Gram-negative genus Vibrio. For Streptomyces
spp., we are interested in the areas of conjugation and pathogenesis. The mechanism by which these ubiquitous soil
organisms exchange genetic information via conjugation is unlike that in any
other bacterial system studied to date. Streptomycetes
almost certainly transfer circular plasmids and possibly chromosomes by a unique
double-stranded mechanism that involves very few plasmid loci.
A particularly interesting aspect of conjugation in these bacteria is
that it is exhibited by both circular and linear plasmids, either of which can
also mobilize the Streptomyces chromosome, whose natural
configuration is also linear. A few Streptomyces spp. are also effective plant
pathogens. One of these, Streptomyces ipomoeae, causes the destructive
sweet potato disease known as soil rot. We are interested in understanding the mechanisms
by which Streptomyces plant pathogens
including S. ipomoeae cause disease.
Specific problems include identifying the genetic determinants of pathogenicity
and studying their regulation as well as understanding how pathogenicity continues
to evolve in these bacteria. Finally,
we are interested in the human pathogen Vibrio
vulnificus, which is a contaminant of oysters and other raw shellfish. Phase variation of V. vulnificus has been known for some time to occur between virulent
encapsulated and avirulent unencapsulated forms. Recently, we discovered a third phase variable
phenotype known as rugose, which we showed is extremely proficient at biofilm
formation. Rugose forms of V. vulnificus may contribute to its pathogenicity
and to its persistence in its natural marine environment.
Ducote, M.J., and G.S. Pettis. 2006. An in vivo assay for conjugation-mediated recombination yields novel results for Streptomyces plasmid pIJ101. Plasmid: In press.
Grau, B.L., M.C. Henk, and G.S. Pettis. 2005. High frequency phase variation of Vibrio vulnificus 1003: isolation and characterization of a rugose phenotypic variant. J. Bacteriol. 187: 2519-2525.
Schully, K.L., and G.S. Pettis. 2003. Separate and coordinate transcriptional control mechanisms link expression of the potentially lethal kilB spread locus to the upstream transmission operon on Streptomyces plasmid pIJ101. J. Mol. Biol. 334: 875-884.
Ducote, M.J., and G.S. Pettis. 2003. Common and distinguishing regulatory and expression characteristics of the highly related KorB proteins of streptomycete plasmids pIJ101 and pSB24.2. J. Bacteriol. 185: 3780-3785.
Zhang, X., C.A. Clark, and G.S. Pettis. 2003. Interstrain inhibition in the
sweet potato pathogen Streptomyces ipomoeae: purification and characterization
of a highly specific bacteriocin and cloning of its structural gene. Appl. Environ.
Microbiol. 69: 2201-2208.