Transposon Mutagenesis of Azospirillum brasilense and Azospirillum lipoferum : Physical Analysis of Tn 5 and Tn 5 -Mob Insertion Mutants

Abstract

Tn 5 -induced insertion mutants were generated in Azospirillum brasilense Sp7 and A. lipoferum SpBr17 by mating with Escherichia coli strains carrying suicide plasmid vectors. The sources of Tn 5 were the suicide plasmids pGS9 and pSUP2021. Kanamycin-resistant Azospirillum colonies appeared from crosses with E. coli at maximum frequencies of 10 −7 per recipient cell. Transposon Tn 5 also conferred streptomycin resistance on Azospirillum colonies as was observed earlier for Rhizobium sp. Eight Tn 5 -induced Km r Sm r A. brasilense Sp7 mutants with reduced nitrogen-fixing capacity were isolated. The potential use of Tn 5 -Mob for labeling and mobilization of Azospirillum -indigenous plasmids was demonstrated by isolating Tn 5 -Mob insertions in the megaplasmids of A. brasilense Sp7.