Gregg S. Pettis

Origin and effects of persistent dsRNA viruses in plants and biological and molecular characterization of acute plant viruses

Our lab has research concerning the Gram-negative bacterial genus Vibrio and the Gram-positive genus Streptomyces. The human pathogen Vibrio vulnificus is a contaminant of oysters and other raw shellfish. Phase variation of V. vulnificus occurs among virulent encapsulated, attenuated unencapsulated, and biofilm-proficient rugose forms. Rugose forms of V. vulnificus may contribute to its persistence in its natural marine environment.

We are interested in understanding the mechanisms by which phase variation occurs in V. vulnificus. Recently, we found that environmental calcium promotes phase variation in this species. For Streptomyces species, we are interested in the areas of pathogenesis and conjugation. A few Streptomyces species are effective plant pathogens. Streptomyces ipomoeae causes the destructive sweetpotato 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. The mechanism by which mycelial Actinobacteria such as Streptomyces species undergo conjugation is unique. Streptomycetes are known to transfer circular plasmids by a novel double-stranded mechanism that involves very few plasmid loci.

A particularly interesting aspect of conjugation in these bacteria is that involves both circular and linear plasmids, either of which can also mobilize the Streptomyces chromosome, whose natural configuration is also linear. We are attempting to elucidate further how conjugation of circular and linear DNA forms occurs in these remarkable organism.

Garrison-Schilling K.L., B.L. Grau, K.S. McCarter, B.J. Olivier, N.E. Comeaux, and G.S. Pettis. 2011. Calcium promotes exopolysaccharide phase variation and biofilm formation of the resulting phase variants in the human pathogen Vibrio vulnificus. Environ. Microbiol.: 13:643-654.

Huguet-Tapia J.C., J.H. Badger, R. Loria, and G.S. Pettis. 2011. Streptomyces turgidiscabies Car8 contains a modular pathogenicity island that shares virulence genes with other actinobacterial plant pathogens. Plasmid 65: 118-124.

Wang J, and G.S. Pettis. 2010. The tra locus of streptomycete plasmid pIJ101 mediates efficient transfer of a circular but not linear version of the same replicon. Microbiol. 156: 2723-2733.

Bignell, D.R.D., J.C. Huguet-Tapia, M.V. Joshi, G.S. Pettis, and R. Loria. 2010. What does it take to be a plant pathogen: genomic insights from Streptomyces species. Antonie van Leeuwenhoek 98:179-194.

Guan D., and G.S. Pettis. 2009. Intergeneric conjugal gene transfer from Escherichia coli to the sweet potato pathogen Streptomyces ipomoeae. Lett. Appl. Microbiol. 49:67-72.

Wang J., K.L. Schully, and G.S. Pettis. 2009. Growth-regulated expression of a bacteriocin, produced by the sweet potato pathogen Streptomyces ipomoeae, that exhibits interstrain inhibition. Appl. Environ. Microbiol. 75:1236-1242