M.S., Rutgers Univ. 1976
B.S., Wilkes Univ. 1974
Office: Lapham 458
Research InterestsOur laboratory is interested in understanding the mechanisms by which bacteria adapt to different host environments. We study as a model system Xenorhabdus nematophila, a motile gram-negative bacterium that engages in both mutualistic and pathogenic host interactions. Xenorhabdus forms a species-specific mutualistic association with the insect-invading nematode, Steinernema carpocapsae. The nematode enters insect hosts and X. nematophila is released from an intestinal vesicle into the insect's body cavity (hemocoel) where it functions as a pathogen. Contraction of the esophagus of the nematode stimulates the forward movement of Xenorhabdus out of the vesicle through a connecting structure that allows the bacteria to enter the intestine and ultimately leave the nematode via the anus. In the hemocoel, Xenorhabdus initially colonizes the connective tissue surrounding the anterior midgut of the host insect. The bacteria proliferate in the insect cadaver reaching high cell densities at which point they produce diverse exoenzymes and antibiotics. The bacteria themselves, as well as the macromolecular degradation they stimulate, provide a nutrient base suitable for nematode reproduction. After several cycles of sexual reproduction the nematodes develop into a dauer juvenile stage that possesses the specialized intestinal vesicle that Xenorhabdus colonizes by a monoclonal process.
I. Comparative genomics
We are involved in a collaborative effort (http://xenorhabdus.danforthcenter.org/) to annotate and analyze the genomes of X. nematophila, that colonizes a single nematode species, and X. bovienii, that forms mutualistic associations with seven different species of steinernematid nematodes. One of the primary goals of this project is to better understand the genetic and molecular basis of host specificity and co-adaptation.
II. Coordinate regulation of motility, exoenzymes and antibiotics
Xenorhabdus nematophila is an emerging model for both mutualism and pathogenicity in different invertebrate hosts. We are analyzing how the EnvZ-OmpR two component system and the flagella sigma factor, FliA(s 28) coordinately regulate the production of lipase, protease, hemolysin and antibiotic activity. The role of this complex regulatory system in the life cycle of Xenorhabdus is being studied.
III. Cell surface proteins
Fimbriae are cell surface appendages involved in adhesion to biotic and abiotic surfaces. Pathogenic bacteria generally possess several fimbrial operons. In contrast, X. nematophila possesses a single complete fimbrial operon. The regulation and function of the fimbrial operon of X. nematophila is presently being investigated. Outer membrane porins allow passive diffusion of solutes into the cell. In X. nematophila, the OpnP porin is highly expressed during exponential growth. We have identified a second porin, OpnS, that is highly expressed during the transition to stationary phase. The regulation and role of this porin in the life cycle of Xenorhabdus is currently being studied.
IV. Competition and antimicrobial products
X. nematophila elaborates bacteriocins that are bacteriophage-derived products that inhibit the growth of closely related bacteria. Xenorhabdus bacteriocins are believed to provide a competitive advantage for growth in the insect cadaver. The bacteriophage genes responsible for the production of the bacteriocin have been identified in the genome of X. nematophila. The function of bacteriocins in suppressing growth of antagonistic competitors in the insect niche is being investigated. X. nematophila also produces several antibiotic compounds that have activities against a broad range of microorganisms. The genes encoding these antibiotics, their regulation and biological significance is under investigation in our laboratory.
Snyder, H., Stock, P., Kim, S., Flores-Lara, Y. and Forst, S. 2007. New Insights into the Colonization and Release Processes of Xenorhabdus nematophila and the Morphology and Ultrastructure of the Bacterial Receptacle of its Nematode Host, Steinernema carpocapsae. Appl. Environ. Microbiol. 66: 1622-1628
Park, D. and Forst, S. 2006. Co-regulation of motility, exoenzyme and antibiotic production by the EnvZ-OmpR-FlhDC-FliA pathway in Xenorhabdus nematophila. Mol Microbiol. 61:1397-412.
Goetsch, M., Owen, H., Goldman, B. and Forst S. 2006. Analysis of the PixA inclusion body protein of Xenorhabdus nematophila. J Bacteriol.188: 2706-10
Forst, S. and Goodner, B. 2006. Comparative bacterial genomics and its use in undergraduate education. Biological Control 38: 47-53.
Kim, D-J. and Forst, S. 2005. Xenorhabdus nematophila: Mutualist and Pathogen. ASM News. 71: 174-178.
Kim, D-J.P. and Forst, S. 2005. The OmpR-FlhDC regulatory circuit and flagella regulon in Xenorhabdus spp. In Pruss, B.M and Matsumura, P. (eds): Global Regulatory Networks in Enteric Bacteria. Research Signpost. Kerala, India.
He, H., Holly A. Snyder, and Steven Forst. 2004 Unique organization and regulation of the mrx fimbrial operon in Xenorhabdus nematophila. Microbiology 150: 1439-1446.
Kim, D-J. Boylan, B. George, N. and Forst, S. 2003. Inactivation of ompR Promotes Precocious Swarming and flhDC Expression in Xenorhabdus nematophila. J. Bacteriol. 185 5290-5294.
Forst, S. and Boylan, B. 2002. Characterization of the pleiotropic phenotype of an ompR strain of Xenorhabdus nematophila. Antonie van Leeuwenhoek 81: 43-49.
P. Prohinar, S. A. Forst, D. Reed, I. Mandic-Mulec & J. Weiss. 2002. OmpR-dependent and OmpR-independent responses of Escherichia coli to sublethal attack by the neutrophil bactericidal/permeability increasing protein. Molecular Microbiology, 43: 1493-1500.
Forst, S. and Clarke, D. 2002. Bacteria-nematode symbioses. In Gaugler (ed.), Entomopathogenic Nematology CABI Publishing, Wallingford, UK.
Delihas N. and Forst S. 2001. MicF: An Antisense RNA Gene Involved in Response of Escherichia coli to Global Stress Factors. Journal of Molecular Biology 313 (1):1-12.
Kim, D-J and Forst, S. 2001. Genomic analysis of the histidine kinase family in bacteria and archaea. Microbiology 147: 1197-1212.
Volgyi, A, Fordor, A and Forst, S. 2000. Inactivation of a novel gene produces a phenotypic variant cell and affects symbiotic behavior in Xenorhabdus nematophilus. Appl. Environ. Microbiol. 66: 1622-1628.
Waukau, J. and Forst, S. 1999. Identification of a conserved sequence involved in transmebrane signal transduction in E. coli . J. Bacteriol. 181: 5534-5538.
Volgyi, A., Fodor, A., Szentirmai, A. and Forst, S. 1998. Phase variation in Xenorhabdus nematophilus. Appl. Environ. Microbiol. 64:1188-1193.
Forst, S. , Dowds, B., Boemare, N. and Stackebrandt, E. 1997. Xenorhabdus spp. and Photorhabdus spp. : Bugs that kill bugs. Ann. Rev. Microbiol. 51: 47-72
Forst, S. and Tabatabai, N. 1997. Role of the histidine kinase, EnvZ, in the production of outer membrane proteins in the symbiotic-pathogenic bacterium, Xenorhabdus nematophilus. Appl. and Environ. Microbiol. 63: 962-968.
Skarphol, K., Waukau, J. and Forst, S. 1997. The role of His-243 in the phosphatase activity of EnvZ in Escherichia coli. J. Bacteriol. 179:1413-1416.
Leonardo, M.R. and Forst, S. 1996. Reexamination of the role of the periplasmic domain of EnvZ in sensing osmolarity signals in Escherichia coli. Mol. Microbiol. 22:405-413.
Forst S, and Nealson K. 1996. Molecular biology of the symbiotic-pathogenic bacteria. Xenorhabdus spp. and Photorhabdus spp. Microbiol. Rev. 60:21-43.
Forst S, Waukau J, Leisman G, Exner M, and Hancock RW. 1995. Functional and regulatory analysis of the OmpF-like porin, OpnP, of the symbiotic bacterium, Xenorhabdus nematophilus. Mol. Microbiol. 18:779-789.
Tabatabai N and Forst S. 1995. Molecular analysis of the ompR or envZ genes in the symbiotic bacterium, Xenorhabdus nematophilus. Mol. Microbiol. 17:643-652.
Forst S, Kalve I, and Durski W. 1995. Molecular analysis of OmpR binding sequences involved in the regulation of ompF in Escherichia coli. FEMS. Micro. Let. 131:147-151.