Effectes of high temperature on survival, symbiotic performance and genomic modifications of bean nodulating Rhizobium strains

High temperatures can affect the survival, establishment and symbiotic properties of "Rhizobium" strains. Bean nodulating "Rhizobium" strains are considered particularly sensitive because on this strains genetic recombinations and/or deletions occur frequently, thus compromising the use of these bacteria as inoculants. In this study "R. tropici" and "R. leguminosarum" bv. "phaseoli" strains isolated from Cerrado soils were exposed to thermal stress and the strains' growth, survival and symbiotic relationships as well as alterations in their genotypic and phenotypic were analysed. After successive thermal shocks at 45ºC for four hours, survival capacity appeared to be strain-specifc, independent of thermo-tolerance and was more apparent in "R. tropici" strains (with the exception of FJ2.21) were more stable than "R. leguminosarum" bv. "phaseoli" strains because no significant phenotypic alterations were observed following thermal treatments and they maintained their original genotypic pattern after innoculation in plants.

Partial characterization of bacteriophages active against rhizobium leguminosarum Isolated from some Egyptian soils

Seventeen rhizobiophages infective against Rhizobium leguminosarwn were isolated from field grown Vicia faba in AI-Ibrahimia [Sharkia Governorate-Egypt]. Morphology, host range and inactivation pattern of the phage to heat and UV-light were studied. Isolated phages had isometric heads and tails which were contractile [2 phages], long and non contractile [7 phages], or very short tails [8 phages]. The phages were members of Bradley's basic morphological groups A, B and C. Most of these phages showed, specificity for their host [R. leguminosarune local strain] and distinct rates of sensitivity against heat and UV