Abstract
Plasmid transformation of the nitrogen-fixing bacterium Azospirillum brasilense is described. A modification of the method of Hanahan [1] was used to transform this bacterium with the 20-kb plasmid pRK290. The efficiency of transformation ranged from 200–1000 transformants per μg of plasmid DNA according to DNA concentration. Ca2+, Mn2+ and K+ were essential for competence, while Rb+ and hexamine cobalt(III) chloride did not appear necessary. The length and the temperature of heat-pulse during transformation affected the efficiency of transformation. The response to different numbers of plasmid molecules was linear, in the range of 0.05–1.0 μg of DNA. No transformants were obtained with pRK290 plasmid DNA linearized with EcoRI. The transformability of different strains of Azospirillum has been compared.
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