الفهرس 
Review of LiteratureOnly 14 pages are availabe for public view
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Abstract
Conjugation transfer is one of the mechanisms allowing diversification and evolution of bacteria. Rhizobium trifolii is a bacterial strain whose habitat is the rhizosphere. It was able to form nodules as a result of the nitrogen – fixing symbiosis. Most of the genetic information involved in the establishment of the symbiosis is localized on plasmid named as the symbiotic plasmid. Rhizobium trifolii is able to establish a symbiotic relationship with the roots of Egyptian clover plants, forming nitrogen fixing nodules. This ability depends on the presence of a set of genes required for nodulation (nod) and nitrogen fixation ( nif and fix). The nod, fix and nif genes are located on symbiotic plasmids. Some plasmids and genomic islands are known for their capacity to carry out horizontal transfer by conjugation. The biological nitrogen fixation have been an important topic in agriculture sector to increase crop yields in poor soils by increase nitrogen in poor lands. The resulting symbiosis was highly specific with the partners involved because of soluble molecular signals regulated by specific genes developmentally regulated association which takes place under the coordinated expression of several symbiosis – related genes in both the plant and the bacteria. Legume – secreted flavonoids initiated the production of nodulation factors in the rhizobia. These secreted, in turn, activate the respone of the host plant to receive the invading rhizobia. This study aimed to improve nodulation and nitrogen fixation in Egyptian clover plants through transfer the cellulase genes from Bacillus thuringiensis and Serratia as donors into Rhizobium trifolii as recipient, to increase the infectability of rhizobia against the host plant to improve nodulation and nitrogen fixation. In this work, two Bt strains and one Serratia strain were used as donors against three Rhizobium trifolii strains as recipients. The results obtained from these investigation were summarized as follows: 1- wild type strains of Bacillus thuringiensis and Rhizobium encoded significant cellulose biodegradation after genome shortening. 2- All transconjugants resulted from the mating between Bt1 and Rh11 expressed significant cellulase activities after curing. 3- All transconjugants results from the mating between Bt2 x Rh6 and Bt2 x Rh11 appeared insignificant differences in cellulase activity before and after curing. 4- The parental strains Rh6 and Rh11 expressed significant cellulase activity after curing. 5- All transconjugants resulted from the mating between Sm x Rh6 and Sm x Rh15 encoded significant cellulase activity after curing. 6- Genome shortening mutants efficiently encoded cellulase in relation to the wild type strains. 7- Cellulase encoded genes were distributed in their location between the bacterial chromosome and plasmids. 8- Plant infection of legumes was affected by Rhizobia cellulases which considered as important determinant in nodulation process. 9- No significant increase was show in nodulation above the mid- parent when the plants were inoculated with transconjugants. 10- There were a significant differences between the different genotypes generated from the conjugation between Bt1 x Rh6 and Bt1 x Rh11 for the number of nodules, as well as, the weight of nodules before curing. 11- No nodules were formed by all Rhizobium genotypes after curing. 12- Significant differences were obtained before curing between the different genotypes generated from the mating between Bt2 x Rh6 and Bt2 x Rh11 for the formation of and the weight of nodules. 13- Significant differences were also obtained between the different genotypes generated from the mating Ser x Rh6 and Ser x Rh15 before curing for the formation of nodules, as well as, the weight of nodules. 14- Non of transconjugants generated from all conjugations appeared significant increase in nodulation above the mid- parent. 15- Insignificant differences were obtained between the genotypes resulted from conjugation between Bt1 x Rh6 and Bt1 x Rh11 in the formation of chlorophyll (a) before curing. 16- Significant differences were obtained between the genotypes generated from the conjugation between Bt1 x Rh6 and Bt1 x Rh11 in the formation of chlorophyll (b) before and after curing. 17- Most of transconjugants did not affect on the formation of significant values of any kind of chlorophyll above the mid- parent. 18- The genotypes resulted from the conjugation between Bt1 x Rh6 and Bt1 x Rh11 appeared significant differences for the formation of chlorophyll (a) after curing. 19- One recombinant genotype resulted from the mating between Bt1 x Rh11 produced significant formation of chlorophyll (a) compared the mid- parent after curing. 20- Significant differences were obtained between the genotypes generated from the conjugation between Bt2 x Rh6 and Bt2 x Rh11 concerning the content of all kinds of chlorophyll in the leaves of clover plants without significant increase by any of recombinants compared the mid- parent. 21- Significant differences were obtained between different genotypes generated from the conjugation between Ser x Rh6 and Ser x Rh15 in the formation of chlorophyll (a) before and after curing, as well as, in the formation of chlorophyll (b) after curing with out any significant increase by recombinants compared the mid- parent. 22-Significant differences were obtained between different genotypes generated from the conjugation between Bt1 x Rh6 and Bt1 x Rh11 concerning the length of roots before and after curing, as well as, for the weight of roots after curing. 23- Significant differences were obtained between the genotypes generated from the conjugation between Bt2 x Rh6 and Bt2 x Rh11 for the length and weight of roots before and after curing without any significant increase by any of transconjugants compared the mid- parents. 24- Significant differences were obtained between the genotypes generated from the conjugation between Ser x Rh6 and Ser x Rh15 concerning the length of roots before and after curing, as well as, the weight of roots before curing without any significant differences in the weight of roots after curing. 25- Non of transconjugants appeared significant increase in the biomass of the roots compared the mid- parent. 26- Due to the genetic interferance between extrachromosomal genomes generated from the different genera the expression of indole acetic acid genes was affected, as a consequences root elongation was not stimulated. This study recommended that genome shortening produced natural in the population of rhizobia. In most cases, cellulases was significantly increased in genome shortening mutants in relation to their wild type. It is evident that the gain of extrachromosomal genome from different genera affected on the expression of the symbiotic genes. Though plant infection was related to cellulase – producing rhizobia.