Ethidium bromide-resistant mutant of Bacillus subtilis.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Bacillus subtilis is a model organism for bacterial genetics.
• Ethidium bromide is a mutagenic intercalating agent that inhibits DNA replication and transcription.
• Understanding resistance mechanisms is crucial for antibiotic development and genetic studies.

Purpose of the Study:

• To characterize a novel ethidium bromide-resistant mutant (EB8) of Bacillus subtilis.
• To investigate the genetic basis and phenotypic expression of ethidium bromide resistance.
• To determine the effect of resistance on cellular processes like RNA synthesis.

Main Methods:

• Isolation and characterization of an ethidium bromide-resistant mutant (EB8).
• Conditional growth studies at varying temperatures and media compositions.
• Transductional mapping to determine genetic linkage.
• Measurement of [5-(3H)] uridine incorporation to assess RNA synthesis.

Main Results:

• The EB8 mutant displayed conditional resistance to ethidium bromide (10 µg/ml) above 30°C during vegetative growth.
• Cross-resistance to acriflavine and proflavine was observed.
• The resistance marker co-transduced with hisA1 at 6% frequency, located to the right of hisA1.
• RNA synthesis in both whole cells and protoplasts of EB8 was resistant to ethidium bromide.

Conclusions:

• EB8 represents a unique Bacillus subtilis mutant with conditional ethidium bromide resistance.
• The resistance is linked to a specific chromosomal locus near hisA1.
• The resistance mechanism confers protection to ribonucleic acid synthesis, suggesting a novel cellular target or pathway involved.