A SPONTANEOUS POINT MUTATION IN THE AAC(6')-IB' GENE RESULTS IN ALTERED SUBSTRATE-SPECIFICITY OF AMINOGLYCOSIDE 6'-N-ACETYLTRANSFERASE OF APSEUDOMONAS-FLUORESCENS STRAIN

The aac(6')-lb' gene from Pseudomonas fluorescens BM2687, encoding an aminoglycoside 6'-N-acetyltransferase type II which confers resistance to gentamicin but not to amikacin, was characterized. Nucleotide sequ ence determination indicated total identity between aac(6')-lb' and th e aac(6')-Ib gene from Pseudomonas aeruginosa BM2656 [1] with the exce ption of a C-to-T transition that results in a serine to leucine subst itution at position 83 of the deduced polypeptide. The aac(6')-lb gene specifies a type I enzyme which confers resistance to amikacin but no t to gentamicin [2]. It thus appears that the point mutation detected is responsible for enzymic altered substrate specificity.