Juan E. González, Ph.D.
Education and Professional Affiliations
B.S., Microbiology and Public Health, Michigan State University
Ph.D., Microbiology & Molecular Genetics, University of California at Los Angeles
Postdoctoral Fellow, Massachusetts Institute of Technology
Dr. González focuses his research on the role of exopolysaccharides in the nodulation of legumes by rhizobia and the molecular genetics of plant-microbe interactions.
Members of the rhizobia are distinguished for their ability to establish a nitrogen-fixing symbiosis with leguminous plants. While many details of this relationship remain a mystery, much effort has gone into elucidating the mechanisms governing bacterium-host recognition and the events leading to symbiosis. Several signal molecules, including plant-produced flavonoids and bacterially produced nodulation factors and exopolysaccharides, are known to function in the molecular conversation between the host and the symbiont.
Work by several laboratories has shown that an additional mode of regulation, quorum sensing, intercedes in the signal exchange process and perhaps plays a major role in preparing and coordinating the nitrogen-fixing rhizobia during the establishment of the symbiosis. Rhizobium leguminosarum, for example, carries a multitiered quorum-sensing system that represents one of the most complex regulatory networks identified for this form of gene regulation.
This review focuses on the recent stream of information regarding quorum sensing in the nitrogen-fixing rhizobia. Seminal work on the quorum-sensing systems of R. leguminosarum bv. viciae, R. etli, Rhizobium sp. strain NGR234, Sinorhizobium meliloti, and Bradyrhizobium japonicum is presented and discussed. The latest work shows that quorum sensing can be linked to various symbiotic phenomena including nodulation efficiency, symbiosome development, exopolysaccharide production, and nitrogen fixation, all of which are important for the establishment of a successful symbiosis.
Many questions remain to be answered, but the knowledge obtained so far provides a firm foundation for future studies on the role of quorum-sensing mediated gene regulation in host-bacterium interactions.
Figure 1: Rhizobium-legume symbiosis model
1. Hoang, H.H., A. Becker and J.E. Gonzalez. 2004. The LuxR Homolog ExpR, in Combination with the Sin Quorum Sensing System, Plays a Central Role in Sinorhizobium meliloti Gene Expression. Journal of Bacteriology. 186:5460-5472.
2. Llamas, I., N. Keshavan and J.E. Gonzalez. 2004. Use of Sinorhizobium meliloti as Incicator for Specific Detection of Long-Chain N-Acyl Homoserine Lactones. Applied and Environmental Microbiology. P. 3715-3723.
3. Gonzalez, J.E. and M.M. Marketon. 2003. Quorum Sensing in Nitrogen-Fixing Rhizobia. Microbiology and Molecular Biology Reviews. P. 574-592.
4. Marketon, M.M., S.A. Glenn, A. Eberhard and J.E. Gonzalez. Quorum Sensing Controls Exopolysaccharide Production in SInorhizobium meliloti. Journal of Bacteriology. P. 325-331.
- Updated: February 6, 2006