Ph.D. Oregon State University, 2000
Either harmful or beneficial bacterium-host interactions can trigger similar host-responses that respectively result in eradication or tolerance of the bacterium. How bacteria can appropriately communicate to a host its benign naturre and how hosts can discriminate between harmful and beneficial bacteria is poorly understood. Using as a model system they symbiosis of the bioluminescent bacterium, Vibrio fischeri, with its animal host, the squid Euprymna scolopes, my research seeks to elucidate how bacteria initiate and maintain long-term associations and how hosts recognize and respond to their desired symbiotic partner.
Figure 1: The hawaiian bobtail Squid, Euprymna scolopes, and cartoon of the light organ
Symbiotic colonization is a dynamic process that requires adaptation by both partners. The host is an active participant during initiation of the symbiotic association, collecting bacteria from the surrounding seawater in mucus it secretes from paired epithelial appendages attached to the light organ and concentrating them near the entrance to the organ that eventually cultures the bacterial symbiont. Although various bacterial species associate with the mucus, only the correct symbiont, V. fischeri, is able to successfully enter into symbiosis by overcoming host-imposed checkpoints. Studies indicate that during the specific cooperative association between V. fisheri and its squid host, the baacterial two-component regulator GacA, coordinately regulates the expression of bacterial traits that alllow it to initiate a benign infection of the squid's light-emitting organ. GacA mutants of V. fischeri are less effective at initiating infection and are also impaired at forming tight aggregates during infection. When its light organ is colonized by V. fischeri, the squid host adapts to this association and, in response to bacterial signals, undergoes a program of changes that leads to the normal develoment of the light organ. One of the most striking changes is apoptosis in and regression of the appendages over a four-day period. GacA mutants that successfully colonize squid light organs do not trigger normal apoptosis during regression of these appendages, implying that delivery of bacterial signals to the squid host is GacA-controlled. Furthermore, GacA mutants fail to trigger cessation of mucus shedding, a colonization response that normally limits further bacterial interaction.
Figure 2: Vibrio fischeri bacteria on a plate are visible with
My current research focus will use the GacA mutant as a basis for identifying and characterization colonization traits. These studies will provide insight into bacteria-derived signals that allow hosts to respond appropriately to beneficial organisms, thus allowing association, without compromising the ability of immune responses to protect the host from pathogenic infection. We are currently utilizing a recently generated DNA microarray of the entire genome of V. fischeri, and will also combine this genomic approach with random mutagenesis screens to discover previously uncharacterized genes and traits that contribute to animal tissue colonization.
E.G. Ruby, M. Urbanowski, J. Campbell, A. Dunn, M. Faini, R. Gunsalus, P. Lostoh, C. Lupp, J. McCann, D. Millikan, A. Schaefer, E. Stabb, A. Stevens, K. Visick, C. Whistler, and E.P. Greenberg. 2005. Complete genome sequence of Vibrio fischeri: A symbiotic bacterium with pathogenic congeners. PNAS 102:3004-3009.
C.A. Whistler and E. G. Ruby. 2003. GacA regulates symbiotic colonization traits of Vibrio fischeri and facilitates its beneficial association with an animal host. 185:7202-7212. Journal of Bacteriology.
C.A. Whistler and L.S. Pierson III. 2003. Repression of phenazine antibiotic production in Pseudomonas aureofaciens strain 30-84 by RpeA. Journal of Bacteriology. 185:3718-3725.
C.A. Whistler, V.O. Stockwell, and J.E. Loper, 2000. Protease Lon regulates antibiotic production and ultraviolet sensitivity of Pseudomonas fluorescens Pf-5. Applied and Environmental Microbiology 66:2718-2725.
C.A. Whistler, N.A. Corbell, A. Sarniguet, W. Ream, J.E. Loper, 1998. The two-component regulators GacS and GacA influence accumulation of the stationary-phase sigma factor s and the stress response in Pseudomonas fluorescens Pf-5. Journal of Bacteriology 180:6635-6641.
J.E. Loper, B. Nowak-Thompson, C.A. Whistler, M.J. Hagen, N.A. Corbell, M.D. Henkels, and V.O. Stockwell, 1997. Biological control mediated by antifungal metabolite production and resource competition. In Proceedings of the Fourth International Workshop on Plant Growth-Promoting Rhizobacteria. A. Ogoshi, K. Kobayashi, Y. Homma, F. Kodama, N. Kondo and S. Akino eds., p. 73-79.