Dr. Gladys Alexandre

Major Research Interests

Bacteria constantly monitor their environment and adapt to changing conditions by modulating the motility behavior and gene expression profiles. Bacteria respond to specific environmental signals that depend on the environment in which they find themselves in as well as their metabolic ability. My laboratory is interested in how motile bacteria use chemotaxis signal transduction pathways to detect and process environmental cues that trigger motility and other cellular responses. Research in the laboratory focuses on two microbial systems: Azospirillum brasilense and Rhizobium leguminosarum. Both microorganisms are plant-growth promoting alpha-proteobacteria. Azospirillum brasilense forms associations with the root system of various host plants (cereals and gramineous). Rhizobium leguminosarum bv. viciae forms nodules within the roots of its host, the pea. Both bacterial species employ multiple chemotaxis signal transduction pathways and associated receptors to detect chemical gradients and modulate their motility behavior. We are interested in comparing how motility and chemotaxis contribute to the adaptation of these bacteria to their environment and the establishment of the plant-microbe associations. We are using microbial physiology and molecular genetics approaches to address these questions and determine which signals are sensed and how they are processed during chemotaxis.

Research in the laboratory is currently supported by a NSF CAREER award.

Lab Images

The many “lifestyles” of the alphaproteobacterium Azospirillum brasilense. A. brasilense can differentiate into several cell types (From top left: swarming cells, swimming cells, example of chemotaxis by swimming cells, flocculated cells and a colony on a rich medium). Complex colony morphologies resulting from the coordinated activities of cells within different zones of the colony are often observed.

Selected Publications

Miller, L. D., Russell, M. H. And G. Alexandre* (2008) Diversity in bacterial chemotactic responses and niche adaptation. Adv. Appl. Microbiol. In press

Bible, A., B. B. Stephens, D. R. Ortega, Z. Xie and G. Alexandre* (2008) Function of a chemotaxis-like signal transduction pathway in modulating motility, cell clumping and cell length in the alpha-proteobacterium Azospirillum brasilense. Journal of Bacteriology In press. (Cover)

Alexandre, G. (2008) A sense of self-worth: energy taxis provides insight into how Helicobacter pylori navigates through its environment. Journal of Bacteriology 190 (9):3095-3097.

Miller, L. D., C. K. Yost, F. Hynes and G. Alexandre* (2007) The major chemotaxis gene cluster of Rhizobium leguminosarum bv. viciae is essential for competitive nodulation. Molecular Microbiology 63 (2): 348-362.

Alexandre*, G., and I. B. Zhulin (2006) Chemotaxis in soil diazotrophs: survival and adaptative response.In: Associative Nitrogen-fixing Bacteria and Cyanobacterial Associations. Series: Nitrogen Fixation – Origins, Applications, and Research Progress, Vol. 5. C. Elmerich and W.E. Newton (eds.), Springer, Germany.

Badger, J.H., T. R. Hoover, Y. V. Brun, R. M. Weiner, M. T. Laub, G. Alexandre, J. Mrázek, Q. Ren, I. T. Paulsen, K. E. Nelson, H. M. Khouri, D. Radune, J. Sosa, R. J. Dodson, S. A. Sullivan, M. J. Rosovitz, R. Madupu, L. M. Brinkac, A. S. Durkin, S. C. Daugherty, S. P. Kothari, M. G. Giglio, L. Zhou, D. H. Haft, J. D. Selengut, T. M. Davidsen, Q. Yang, N. Zafar, and N. L. Ward (2006) Comparative genomic evidence for a close relationship between the dimorphic prosthecate bacteria Hyphomonas neptunium and Caulobacter crescentus. Journal of Bacteriology 188: 6841-6850.

Stephens, B. B., S. N. Loar and G. Alexandre* (2006) The role of CheB and CheR in the complex chemotactic and aerotactic pathway of Azospirillum brasilense. Journal of Bacteriology 188: 4759-4768.

Su, S., B. B. Stephens, G. Alexandre and S. K. Farrand (2006) Lon protease of the alpha-proteobacterium Agrobacterium tumefaciens is required for normal growth, cellular morphology and full virulence. Microbiology 152: 1197-1207.

Greer-Phillips, S., B. B. Stephens and G. Alexandre* (2004) An energy taxis transducer promotes plant root colonization by Azospirillum brasilense. Journal of Bacteriology 186: 6595-6604.

Alexandre*, G., Greer-Phillips, S. and I. B. Zhulin (2004) Ecological role of energy taxis in microorganisms. FEMS Microbiology Reviews 28: 113-126.

Greer-Phillips S. E, G. Alexandre, B. L. Taylor, and I. B. Zhulin (2003) Aer and Tsr guide Escherichia coli in spatial gradients of oxidizable substrates. Microbiology 149: 2661-2667.

Alexandre, G. and I. B. Zhulin (2003) Different evolutionary constraints on chemotaxis proteins CheW and CheY revealed by heterologous expression studies and protein sequence analysis. Journal of Bacteriology 185: 544-552.

Hauwaerts, D., G. Alexandre, S. K. Das, J. Vanderleyden, and I. B. Zhulin (2002) A major chemotaxis gene cluster in Azospirillum brasilense and relationships between chemotaxis operons in alpha-proteobacteria. FEMS Microbiology Letters 208: 61-67.

Alexandre, G., and I. B. Zhulin (2001) More than one way to sense chemicals. Journal of Bacteriology 183: 4681-4686.

Alexandre, G., S. E. Greer, and I. B. Zhulin (2000) Energy taxis is the dominant behavior in Azospirillum brasilense. Journal of Bacteriology 182:6042-6048.

Alexandre, G., and I. B. Zhulin (2000) Laccases are widespread in bacteria. Trends in Biotechnology 18: 41-42.

Alexandre, G., R. Bally, B. L. Taylor, and I. B. Zhulin (1999) Loss of cytochrome c oxidase activity and acquisition of resistance to exogenous quinones in a laccase-positive variant of Azospirillum lipoferum. Journal of Bacteriology 181: 6730-6738.

Alexandre*, G., and R. Bally (1999) Emergence of a laccase-positive variant of Azospirillum lipoferum occurs via a two-step phenotypic switching process. FEMS Microbiology Letters 174: 371-378.

Alexandre*, G., R. Rohr, and R. Bally (1999) A phase variant of Azospirillum lipoferum lacks a polar flagellum and constitutively expresses mechanosensing lateral flagella. Applied and Environmental Microbiology 65: 4701-4704.

Bouillant, M.L., L. Miche, O. Ouedraogo, G. Alexandre, C. Jacoud, G. Salle, and R. Bally (1997) Inhibition of Striga seed germination associated with sorghum growth promotion by soil bacteria. Comptes Rendus de l’Academie Des Sciences Serie III – Sciences de la Vie (Proceedings of the French Academy of Sciences – Life Science Series) 320: 159-162.

Alexandre*, G., C. Jacoud, D. Faure, and R. Bally (1996) Population dynamics of a motile and non-motile Azospirillum lipoferum strain during rice colonization and motility variation in the rhizosphere. FEMS Microbiology Ecology 19: 271-278.

*Corresponding author