Bacterial Physiology and Viruses: Structure and Life Cycles

Posted on Nov 16, 2024 in Biology

Bacterial Physiology

Bacterial culture media are aqueous solutions with salts, minerals, and organic nutrients. These components support bacterial metabolism, growth, and reproduction. Bacteria are cultivated in liquid media in test tubes. Like all living beings, bacteria perform nutrition, interaction, and reproduction functions.

Functions of Nutrition

Bacteria exhibit diverse metabolic types: photoautotrophs (e.g., green bacteria, cyanobacteria), photoheterotrophs (requiring light and organic molecules), chemoautotrophs (e.g., nitrifying bacteria), and chemoheterotrophs.

Interaction Functions

Many bacteria are motile, moving via flagella or by contractions on solid surfaces. Spore formation is a common response to environmental changes, providing resistance.

Reproduction Functions

Bacteria reproduce asexually through binary fission, preceded by DNA replication. The resulting colonies are clones. Bacteria also have parasexual mechanisms for genetic exchange, even between different species:

  • Conjugation: DNA transfer from a donor to a recipient bacterium through a sex pilus.
  • Transduction: Genetic exchange via viral vectors carrying bacterial DNA.
  • Transformation: Uptake of free DNA fragments from lysed bacteria.

Viruses

Viruses are microscopic particles consisting of a nucleic acid (viral genome) enclosed in a protein capsule (capsid), sometimes with a membranous envelope. They lack cellular structure and metabolic enzymes, existing as inert virions outside host cells.

Viral Structure

Viruses have three main parts:

  • Viral Genome: DNA or RNA, single or double-stranded, linear or circular.
  • Capsid: Protein coat protecting the genome, determining shape (icosahedral, helical, complex).
  • Membranous Envelope: Lipid bilayer with viral and host glycoproteins, aiding in host cell recognition and entry.

Viroids and Prions

Viroids: Small RNA molecules infecting plant cells.

Prions: Misfolded proteins causing diseases.

Viral Life Cycle

The viral life cycle includes:

  • Fixation or adsorption
  • Penetration
  • Replication of the viral genome and synthesis of capsomers
  • Assembly of new viruses
  • Lysis and release

Lytic Cycle of Bacteriophage T4

  1. Fixation or Adsorption: Attachment to the bacterial cell wall.
  2. Penetration: Injection of viral DNA into the host cell.
  3. Eclipse Phase: Synthesis of viral RNA and DNA replication.
  4. Assembly Phase: Formation of new virions.
  5. Lysis or Release Phase: Cell lysis and release of new virions.

Antibiotic Production

Industrial antibiotic production has increased significantly since the 1950s, driven by:

  • Discovery of high-yield microbial species.
  • Improved culture media and techniques.
  • Selection of mutant strains with enhanced antibiotic production.
  • Advanced extraction methods.