Biosynthesis of 3″-demethyl-gentamicin C components by genN disruption strain of Micromonospora echinospora and test their antimicrobial activities in vitro

Gentamicin consists primarily of four components, which have different patterns of methylation at C-6′ position. The methyl groups have a significant impact on gentamicin antimicrobial activity. Sequence analysis predicted that GenN was a methyltransferase in the gentamicin biosynthetic pathway. To study the function of genN, it was disrupted in Micromonospora echinospora. The genN disruption strains produced 3″-N-demethyl-gentamicin C complex instead of the gentamicin C complex. In this study, 3″-N-demethyl gentamicin C1a was purified from the broth of disruption strain, and its structure was elucidated using MS and NMR. Besides 3″-N-demethyl products corresponding to gentamicin C1a, C2, and C2a, two 3″-N-demethyl products corresponding to gentamicin C1 were detected, which were concluded as C-6′ epimers originating from decreased substrate specificity of 6′-N methyltransferase. To explore the effects of 3″-N-methyl on gentamicin antimicrobial activity, antimicrobial activity of these demethyl gentamicin analogues were tested in vitro. 3″-N-Demethyl gentamicin components have identical activity with corresponding components of gentamicin. The results of bioassays showed that the 3″-N-methyl group has little impact on gentamicin activity. However, these highly bioactive compounds afforded a unique opportunity for creating new and high potent aminoglycoside antibiotics.