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Isolation, characterization, and inoculation of N2-fixing bacteria from dicotyledonous plants

Canadian Journal of Microbiology (Impact Factor: 1.2). 02/2011; 32(12):912-916. DOI: 10.1139/m86-168

ABSTRACT N2-flxing (acetylene-reducing) bacteria were isolated from roots of five species of wild plants in southern New Mexico. Ground cherry (Physalis wrightii) had the highest frequency of roots with N2-fixing bacteria. Acetylene reduction rates of subcultures were comparable with rates exhibited by Azospirillum (300–500 nmol ethylene∙h−1). Three isolates from ground cherry were characterized to the generic level and one to the level of genus and species. Three of these isolates were identified as Enterobacter spp, while the fourth isolate was identified as Azospirillum brasilense. Inoculation of ground cherry with N2-fixing isolates had minimal effects on plant growth, plant nitrogen content, or plant acetylene reduction activity 7 weeks after inoculation. Comparisons between uninoculated and inoculated plants were generally not statistically significant. Significant acetylene reduction activity and high numbers of N2-fixing bacteria occurred only on the roots of plants grown with little or no added nitrogen.

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    ABSTRACT: A total of 17 culturable nitrogen-fixing bacterial strains associated with the roots of wheat growing in different regions of Greece were isolated and characterized for plant-growth-promoting traits such as auxin production and phosphate solubilization. The phylogenetic position of the isolates was first assessed by the analysis of the PCR-amplified 16S rRNA gene. The comparative sequence analysis and phylogenetic analysis based on 16S rRNA gene sequences show that the isolates recovered in this study are grouped with Azospirillum brasilense, Azospirillum zeae, and Pseudomonas stutzeri. The diazotrophic nature of all isolates was confirmed by amplification of partial nifH gene sequences. The phylogenetic tree based on nifH gene sequences is consistent with 16S rRNA gene phylogeny. The isolates belonging to Azospirillum species were further characterized by examining the partial dnaK gene phylogenetic tree. Furthermore, it was demonstrated that the ipdC gene was present in all Azospirillum isolates, suggesting that auxin is mainly synthesized via the indole-3-pyruvate pathway. Although members of P. stutzeri and A. zeae are known diazotrophic bacteria, to the best of our knowledge, this is the first report of isolation and characterization of strains belonging to these bacterial genera associated with wheat.
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