Microbiology · MU Sofia

9. Bacterial Physiology = Chemical Composition, Bacterial Metabolism, Bacterial Productivity.

Covers the chemical make-up of bacterial cells, including the cytoplasmic membrane, peptidoglycan cell walls with Gram-positive, Gram-negative and mycobacterial differences, chromosomes and plasmids, ribosomes, inclusions, appendages and endospores. It then turns to metabolism, classifying bacteria by carbon and energy source and by oxygen requirement, and outlines fermentation and respiration. The final section describes bacterial productivity, including quorum sensing, biofilms, virulence factors, environmental roles and industrial uses.

Inside: 4 sections · 5 labelled pictures · 12 flashcards · 5 min

Topic 9 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 4 sections, about 767 words (5 min of reading), with 12 flashcards.

In this note

  1. Bacterial physiology, Bacterial Metabolism, Bacterial Productivity
  2. Chemical Composition
  3. Bacterial Metabolism
  4. Bacterial Productivity

Chemical Composition

  • Bacteria are prokaryotes.
  • They lack membrane-bound organelles.
  • The cytoplasmic membrane is a phospholipid bilayer but contains no cholesterol (except for Mycoplasmas). Oxidative phosphorylation occurs here, replacing mitochondria for ATP synthesis.
  • The cell wall provides structural support and is primarily composed of peptidoglycan (also known as murein).
  • Peptidoglycan is a polymer of disaccharides (N-acetylglucosamine - NAG and N-acetylmuramic acid - NAM) cross-linked by amino acids.
  • Gram-positive cell walls have a thick peptidoglycan layer with extensive cross-linking, lipoteichoic acid, teichoic acid, polysaccharides, and proteins. Teichoic acid is antigenic.
  • Gram-negative cell walls have a thin peptidoglycan layer with little cross-linking, and a porous outer membrane containing lipopolysaccharide (LPS) on its outer surface. LPS is responsible for the pathogenesis of Gram-negative infections.
  • Mycoplasmas are exceptions as they lack a cell wall and peptidoglycan. They incorporate sterols from the host into their membranes.
  • Mycobacteria have a peptidoglycan layer intertwined with an arabinogalactan polymer and surrounded by a wax-like lipid coat of mycolic acid, cord factor, waxD, and sulfolipids. This makes them acid-fast.
  • The bacterial chromosome is typically a single, circular, double-stranded DNA molecule located in the cytoplasm in a region called the nucleoid. Histones are generally absent.
  • Plasmids are smaller, extra-chromosomal, circular, double-stranded DNA molecules that

replicate independently of the chromosome. They often contain genes for antibiotic resistance or virulence factors.

  • Ribosomes are 70S (composed of 50S and 30S subunits). They are the sites of protein synthesis.
  • Cytoplasmic inclusions can store reserve nutrients like glycogen granules and metachromatic granules (volutin - stored phosphate).
  • Flagella, used for motility, are composed of the protein flagellin.
  • Pili (fimbriae), used for attachment or conjugation, are protein tubes.
  • Bacterial spores (endospores) are resistant structures that contain peptidoglycan, cytoplasm, water, and bacterial DNA. They also contain dipicolinic acid complexed with calcium ions.

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