UDK 631.461.5:575 ESTIMATION OF PHENOTYPIC PRESENTATIONS OF BACTERIAL GENES, CONTROLLING THE EFFICIENCY OF NITROGEN-FIXING SYMBIOSIS WITH PLANTS O.P. Onishchuk, N.A. Provorov, N.I. Vorob’ev, B.V. Simarov All-Russia Research and Development Institute of Agricultural Microbiology, RAAS, St.Petersburg – Pushkin-8 196608, Russia e-mail: provorov@newmail.ru Received January 11, 2010 S u m m a r y The collection of recombinant species of nodule bacterium of lucerne (Sinorhizobium meliloti) with additional copies of dicarboxylic acid transport gene (process, limiting nitrogen fixation) was used and the authors shown, that the symbiosis efficiency is limiting by the plant inability to absolute involvement of biological nitrogen in growth process and the transfer to above-ground organs nitrogen transport forms, accumulation of which in roots and nodules inhibits an energy entry in bacteroides. <...> On the data of factor analysis of vegetative experiment results the amplification succinate permease dctA structure gene in complex with specific transcription regulator dctBD increases the symbiosis efficiency regardless of plant variety and vegetation conditions, but the amplification of nifA and ntrA genes (nonspecific regulators of dctA gene) required for the increase of N2-fixing activity only at unfavorable for it conditions. <...> Keywords: symbiotic nitrogen fixation, nodule bacteria, leguminous plants, genetic construction, dicarboxylic acids, factorial analysis, symbiotic efficiency, competitiveness, ecologically safe soil tillage. <...> Genetic engineering and introduction in plant growing of highly efficient nitrogen-fixing symbiotic bacteria are limited by low reproducibility of the phenotype “increased efficiency of symbiosis”, which use to be the result of growing conditions and genotypes of host plants - highly polymorphic cultivars leveling genotypic differences of microsymbionts. <...> The prospects and constraints for genetic engineering of nitrogen-fixing microsymbionts. <...> Plant symbioses with nitrogenfixing bacteria have great ecological and agronomic importance as the source of plant-available nitrogen for environmentally sound farming systems and plant growing (1-3). <...> The most effective symbioses are morphologically supported interactions of plants with rhizobia (legumes), actinomycetes Frankia (actinorhiza formed by bipartites the group Rosid I) and cyanobacteria Nostoc (syncyanoses characteristic for thallophytes, some gymnosperms and flowering plants). <...> These symbioses provide mixotrophic nitrogen nutrition in large majority of cultivated crops, though correlation <...>