CeBiTec Colloquium: 2008/05/15 Prof. Dr. Jose Enrique Ruiz Sainz, Faculty of Biology, Department of Microbiology, University of Seville

2008/05/15, 12:30

CeBiTec Laboratory Building, Room G2-104

Genetic and agronomic studies on Sinorhizobium fredii

Abstract:
Many isolates of Sinorhizobium fredii are able to fix nitrogen with Asiatic and American soybean cultivars. Our genetic work on S. fredii strain HH103 is mainly focussed on the bacterial surface polysaccharides. In this seminar, our results focused on rhizobial capsular polysaccharides (KPS) will be presented. The structure of the KPS produced by different S. fredii strains has been determined. Apparently, there is a correlation between the composition of the KPS repeating unit and the cultivar specificity shown by the S. fredii strains investigated so far. S. fredii HH103 mutants affected in rkp genes of the rkp-1 region form less nodules on soybean roots. Nitrogen fixation is also severely reduced. The symbiotic capacity of these mutants to nodulate and fix nitrogen with Vigna unguiculata is similar to that of the wild-type strain HH103. Mutants affected in the rkp-1 region do not show alterations in their LPS electrophoretic profiles. Mutants affected in rkp genes of the rkp-3 region only form seudonodules
(or small non-fixing nodules) with soybean and V. unguiculata. These mutants also show alterations in their LPS electrophoretic profiles. This LPS alteration, rather than the incapacity of the rkp-3 mutants to produce KPS, could be the reason why the symbiotic impairment of the rkp-3 mutants is higher than that of rkp-1 mutants.