in The Department of Plant Sciences

College of Agriculture and Life Sciences, Forbes Building 303,
P.O. Box 210036,
Tucson AZ 85721-0036
(520) 621-1977, FAX (520) 621-7186

Dr. Leland S. Pierson III
Professor and Division Chair

B.A.     Microbiology, University of California, Davis
Ph.D.  Microbiology, Washington State University

Chair, The University of Arizona Institutional Biosafety Committee
Chair, Microbiology Curriculum Committee

e-mail: lsp@u.arizona.edu

Areas of Interest:

Microbial gene regulation; microbial community interactions; biofilms, biological control of soil-borne plant pathogens.

Research Goals:
Bacteria exist within complex communities termed biofilms on solid surfaces, including plant roots. Members of these communities interact both cooperatively and competitively to enable the inhabitants to perform functions not possible by single organisms. Secondary metabolites play important roles in the establishment, development and dispersal of biofilm communities. Antibiotics are secondary metabolites nonessential for primary growth but important in bacterial survival. Antibiotic-producing plant-associated bacteria were first identified because of their toxicity to plant pathogens. Work on many systems resulted in the long-standing hypothesis that antibiotics are primarily a competitive mechanism and studies on antibiotics have contributed greatly to our understanding of their mechanisms of action and the regulation of secondary metabolites.
Our laboratory focuses on the regulation of phenazine antibiotics and other secondary metabolites in the free-living root-associated bacterium Pseudomonas aureofaciens strain 30-84. In order to optimize desired plant-associated microbial traits, including biological control, it is necessary to (1) understand how specific regulatory networks control the expression of the genes encoding desired traits and (2) understand the effects of the community on the expression of these traits. This requires an understanding of the range of functions specific secondary metabolites play for the producing organism.
Our research has shown that phenazine production is regulated by a complex interconnected sensory system and that phenazine production is influenced directly by other members of the rhizosphere community-- results not consistent with competition as their primary role. Why strain 30-84 produces multiple phenazine derivatives whereas other strains do not is also unclear. Recent data from our lab and others suggest additional roles for phenazines including involvement in cell adhesion and energy generation. Mutants of strain 30-84 defective in phenazine production were defective in cell adhesion/biofilm formation and the addition of different semi-purified phenazines had different effects on restoration of adhesion. Work on other phenazines indicates they may also play a role in respiration as exogenous electron shuttles and/or promote Fe-acquisition through mineral reduction. We hypothesize that antibiotics play multiple roles in the lifestyle of the producing bacterium and we are focused on identifying and understanding these additional phenazine functions for strain 30-84 in microbial physiology, microbe-microbe and plant-microbe interactions.

Selected Publications (last five years):

Morello, JE, Pierson, EA, and LS Pierson III. 2004. Negative cross-communication among wheat rhizosphere bacteria: Effect on antibiotic production by the biological control bacterium Pseudomonas aureofaciens 30-84. Appl. Environ. Microbiol. 70:XXXX-XXXX.

McLean, RJC, LS Pierson III and C Fuqua. 2004. A simple screening protocol for the identification of quorum signal antagonists. J. Microbiol. Methods (in press).

Loper, J.E., Paulsen, I., Thomshow, L., Pierson, L.S., Kobayashi, D., Pierson, E., Press, C., Mavrodi, D., Reddy, R. 2003. Genomics of Pseudomonas fluorescens Pf-5: insights in biological control. Phytopathology 93:S108.

Wijertne, EMK, Turbyville, TJ, Zhang, Z, Bigelow, D, Pierson, LS III, VanEtten, HD, Whitesell, L, Canfield, LM, and Gunatilaka, AAL. 2003. Cytotoxic constituents of Aspergillus terreus from the rhizosphere of Opuntia versicolor of the Sonoran Desert. J. Nat. Prod.66:1567-1573.

Whistler, CA and L.S. Pierson III. 2003. Repression of phenazine antibiotic production in Pseudomonas aureofaciens strain 30-84 by RpeA. J. Bacteriol. 185:3718-3725.

Chancey, ST, Wood, DW, Pierson, E.A., and L.S. Pierson III. 2002. Survival of GacS/GacA mutants of the biological control bacterium Pseudomonas aureofaciens 30-84 in the wheat rhizosphere. Appl.Environ. Microbiol. 68: 3308-3314.

Loh, J. Pierson, EA, Pierson, LS III, Stacy, G, and A. Chatterjee. 2002. Quorum sensing in plant-associated bacteria. Curr. Opin. Plant Biol. 5:1-5.

Zhang, Z., and Pierson, L.S. III. 2001. A second quorum sensing system regulates cell surface properties but not phenzaine antibiotic production in Pseudomonas aureofaciens. Appl. Environ. Microbiol. 67:4305-4315

Pierson, L.S. III. 2000. Bacterial signaling: Identification of N-acyl-homoserine lactone-producing bacteria. The Plant Health Instructor DOI:10.1094/PHI-I-2000-1214-01

Pierson, L.S. III
. 2000. Expanding the club: engineering plants to talk to bacteria. Trends in Plant Sciences 5:89-91

Chancey, S.T., Wood,D.W., and Pierson, L.S. III. 1999. Two-component transcriptional regulation of N-acyl-homoserine lactone production in Pseudomonas aureofaciens. Appl. Environ. Microbiol. 65:2294-2299.

Pierson, L.S. III, Wood, D.W., and Beck von Bodman, S. 1999. Quorum sensing in plant-associated bacteria. In: Cell-Cell Signaling, Dunney, G.M., and Winans, S.C., eds. pp.101-116, American Society for Microbiology Press, Washington, D.C.

Pierson, Elizabeth A., Wood, Derek W., Cannon, Jeffrey A., Blachere, Francoise M. and Pierson, Leland S. III. 1998. Interpopulation Signaling via N-Acyl-Homoserine Lactones among Bacteria in the Wheat Rhizosphere. MPMI 11: 1078-1084.

Pierson, L.S. III, Wood, D.W., Pierson, E.A., and Chancey, S.T.  1998.  Homoserine lactone-mediated gene regulation in plant-associated bacteria.  Annv. Rev. Phytopathol. 36:207-225.

Pierson, L.S. III, Wood, D.W., Pierson, E.A., and Chancey, S.T. 1998. N-acyl-homoserine lactone-mediated gene regulation in biological control by fluorescent pseudomonads: current knowledge and future work. Eur. J. Plant Pathol. 104:1-9.

Wood, D.W., Gong, F., Daykin, M.M., Williams, P., and Pierson, L.S. III. 1997. N-acyl-homoserine lactone-mediated regulation of phenazine gene expression by Pseudomonas aureofaciens 30-84 in the wheat rhizosphere. J. Bacteriol. 179:7663-7670.

Zhu, Y., Pierson, L.S. III., and Hawes, M.C. 1997. Induction of microbial genes for pathogenesis and symbiosis by chemicals from root border cells. Plant Physiology 115:1691-1698.

For More Information:
Dr. Leland Pierson III
The University of Arizona
303 Forbes Building
P.O. Box 210036
Tucson, AZ 85721-0036

Tel: (520) 621-9419
Fax: (520) 621-7186

last updated: August 18, 2006
© 2004 The University of Arizona. All contents copyrighted. All rights reserved.