Dr. Alejandro García De Los Santos
Genome Engineering Program
Center for Genomic Sciences
B.Sc. Biology. 1988. Faculty of Science. National Autonomous University of Mexico; Ph.D. Basic Biomedical Research. 1997. Nitrogen Fixation Research Center. National Autonomous University of Mexico; Postdoctoral Dept. Biological Sciences, University of Calgary. Canada (1999-2000);
Identification of plasmid-encoded genes involved in the adaptation of Rhizobium etli to the rhizosphere of Phaseolus vulgaris using genetic and genomic approaches. Rhizobia are Gram-negative bacteria that can grow saprophitically in the rhizosphere of legume plants or as nitrogen-fixing simbionts within root nodules. Whereas the bacterial genes required for nodulation and nitrogen fixation have been studied in detail, little is known about the genetic information allowing rhizobia to survive in the soil and root environment. In order to contribute to this knowledge we are looking for genes involved in the adaptation of Rhizobium etli CFN42 to the rhizosphere of Phaseolus vulgaris. The genome of this bacterium consists of one circular chromosome (4.3 Mb) and six plasmids (p42a–p42f) ranging in size from 184 to 640 kb. We have isolated derivatives of the parental strain cured of each plasmid as well as cured of multiple plasmids (Brom et al 1992). Co-inoculation experiments on bean plants demonstrate that derivatives cured of each plasmid are significantly less competitive for root nodulation than the wild type strain (Brom et al 1992). The most drastic decrease in competitivity for nodulation has been observed in a multiple plasmid-cured derivative (Brom et al 2000). These data indicate that plasmid-encoded genes play an important role in the adaptation of R. etli to the rhizosphere of bean plants.
A. García-de los Santos and S. Brom. 1997. “Characterization of two plasmid-borne lpsbï ï loci of Rhizobium etli required for lipopolysaccharide synthesis and for optimal interaction with plants”. Mol. Plant-Microbe Interact. 10: 891-902.
A. García-de los Santos, S. Brom and D. Romero. 1996. “Rhizobium plasmids in bacteria-legume interactions”. World J. Microbiol. Biotechnol.12:119-125.
Brom, S., A. García de los Santos, T. Stepkowski, M. Flores, G. Dávila, D. Romero and R. Palacios. 1992. “Different plasmids of Rhizobium leguminosarum bv. phaseoli are required for optimal symbiotic performance”. J. Bacteriol. 174:5183-5189.