The analysis of PFGE patterns allowed determination of the genome size of the Azospirillum strains studied which varied from 4.8 to 9.7 Mbp. Azospirillum lipoferum has the largest and A. iraquense the smallest genome size in the genus. At least two megareplicons of each strain hybridized with 16S and 23S rDNA probes, suggesting the presence of multiple chromosomes in Azospirillum, some of which were linear. The profiles were clearly different among the strains. The rrn copy number of A. brasilense FP2 was estimated to be at least five by hybridization of restricted total DNA, suggesting that the chromosomes may have more than one copy of the 16S rRNA gene. Our results indicate that Azospirillum genome topology is highly plastic and variable.
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