4BBY1070 Genetics and Molecular Biology - Genetics of Bacteria

Lecture by Dr. Shirley Coomber

Learning Objectives:

• Understand bacterial haploidy
• Cell division in prokaryotes
• Aseptic culture and media for bacterial growth
• Transformation process
• Enhancing E. coli competency for gene cloning
• Lysis cycle of T4 bacteriophage
• Generalized transduction in bacteriophages
• Gene exchange by conjugation
• F plasmid transfer and integration in E. coli
• Hfr strains and gene transfer
• Naturally occurring plasmids

Working with Microorganisms:

Growth Media

• Liquid Medium: Nutrient broth rich in yeast extract and casein (e.g., LB)
• Minimal Media: Contains essential ions and glucose; used for minimal growth conditions
• Growth Phases:
  • Lag phase: Adaptation
  • Exponential phase: Rapid growth
  • Stationary phase: Nutrient limitation

Bacterial Genetics:

• Single chromosome of circular, double-stranded DNA
• Genes organized into operons
• E. coli as a model organism
  • First complete DNA sequence in 1997
  • 4288 protein-coding genes, 7 rRNA operons, 86 tRNA genes

Genetic Exchange Mechanisms:

Transformation

• Uptake of environmental DNA fragments by bacteria
• Competency enhanced in labs using solutions (e.g., CaCl2)
• Example: pGLO plasmid transformation

Transduction

• Bacteriophages transfer DNA between bacteria
• Lytic and lysogenic cycles
• Use of viruses as vectors in gene therapy

Conjugation

• DNA exchange via direct cell contact
• F plasmid facilitates transfer through conjugation pilus
• Hfr strains: High frequency recombination strains
• R plasmids: Carry antibiotic resistance and tra genes

Practical Applications and Examples:

• Growth on agar plates: Colony formation from single cells
• Use of different media to analyze genetic traits (e.g., lac+ vs. lac-)
• Practical lab sessions involving transformation and gene expression studies

Summary:

• Bacteria exchange DNA through transformation, transduction, and conjugation
• Understanding these processes aids in genetic analysis and molecular biology research