Gentamicin-resistance determinants confer background-dependent hygromycin B resistance

Area of Science:

• Microbiology
• Molecular Biology
• Antibiotic Resistance

Background:

• Micromonospora strains producing aminoglycosides display resistance to similar antibiotics.
• They are typically susceptible to aminoglycosides with different aminocyclitol substitutions.
• Unexpectedly, these strains also showed resistance to hygromycin B, which has a distinct structure and mechanism of action.

Purpose of the Study:

• To investigate the mechanism behind hygromycin B resistance in aminoglycoside-producing Micromonospora.
• To determine if known aminoglycoside resistance genes confer hygromycin B resistance.
• To explore the strain-dependent nature of this resistance.

Main Methods:

• Cloning of resistance genes (sgm, grm) into heterologous hosts (Streptomyces lividans, E. coli).
• Introduction of resistance genes into M. melanosporea.
• Testing of transformants for resistance to various aminoglycosides, including hygromycin B.
• Comparison of resistance gene expression across different bacterial backgrounds.

Main Results:

• Cloned genes conferred expected aminoglycoside resistance in S. lividans and E. coli, but not hygromycin B resistance.
• In M. melanosporea, the same genes conferred resistance to hygromycin B.
• Only the kgm gene facilitated hygromycin B resistance, and only in the M. melanosporea background.
• This highlights a strain-dependent expression of hygromycin B resistance.

Conclusions:

• Aminoglycoside resistance in Micromonospora is not solely determined by the resistance genes but also by the host genetic background.
• A novel mechanism for hygromycin B resistance exists in M. melanosporea, influenced by strain-specific factors.
• Further research is needed to elucidate the precise mechanism of this background-dependent resistance.