Comprehensive Study Notes on Brock Biology of Microorganisms: Chapter 1

Microorganisms: Tiny Titans of the Earth

Definition: Microorganisms (microbes) are microscopic life forms that are typically too small to be seen by the naked human eye. They exhibit immense diversity in both form and function.
Habitat and Distribution: Microbes inhabit every environmental niche on Earth that supports biological life. They exist as single-celled organisms, complex multicellular structures, or organized microbial communities.
Global Abundance: The total count of microbial cells on Earth is estimated to be approximately $2 \times 10^{30}$ cells.
Evolutionary and Ecological Significance:
- Microorganisms represent the oldest form of biological life on Earth.
- They constitute a major fraction of the planet's total biomass.
- They surround and interact with all macroscopic plants and animals.
- Microbes directly influence human existence through infectious diseases, food and water supply systems, agricultural soil fertility, animal digestion, industrial fermentations, and global bioenergy production.
Essential Laboratory Tools:
- Microscopy: Optical techniques used to magnify and resolve microscopic cellular structures.
- Culture: A population of microbial cells grown in or on a nutrient medium.
- Medium: A liquid or solid mixture containing all chemical nutrients required for microbial cell growth.
- Growth: An increase in total cell number resulting from binary fission or cell division.
- Colony: A macroscopic, visible mass of microbial cells formed on solid medium, typically containing millions or billions of individual cells derived from a single parent cell.
Model Systems: Microorganisms serve as fundamental model systems for studying universal life processes in molecular biology, biochemistry, genomics, and molecular genetics.

Microbial Applications

Structure and Activities of Microbial Cells

Definition of a Cell: A living compartment enclosed by a membrane that dynamically interacts with its external environment and other cells.
Universal Elements of Cellular Structure:
- Cytoplasmic Membrane: A selectively permeable barrier that separates the internal aqueous cytoplasm from the external environment.
- Cytoplasm: An aqueous solution containing macromolecules, small organic molecules, inorganic ions, and ribosomes.
- Ribosomes: Macromolecular structures responsible for protein synthesis (translation).
- Genome: The complete set of genes present within an organism, composed of double-stranded DNA.
- Cell Wall: A rigid structural layer present in most microbes (external to the membrane) that confers structural strength and protects against osmotic lysis.
Prokaryotic versus Eukaryotic Structural Organization:
- Prokaryotic Cells (Domains Bacteria and Archaea):
  - Lack membrane-bound intracellular organelles.
  - Lack a membrane-enclosed nucleus; genetic material aggregates in an unbounded region called the nucleoid.
  - Typically possess a single, circular chromosome.
  - May harbor plasmids: small, extrachromosomal circular DNA molecules conferring non-essential specialized traits such as antibiotic resistance.
  - Possess small, compact genomes ranging from $0.5 \times 10^6$ to $10 \times 10^6$ \text{ base pairs} ( $0.5$ to $10$ \text{ megabase pairs}).
- Eukaryotic Cells (Plants, Animals, Fungi, Algae, Protozoa):
  - Contain membrane-bound organelles including mitochondria, chloroplasts, Golgi apparatus, and endoplasmic reticulum.
  - DNA is housed within a double-membrane-bound nucleus as linear chromosomes.
  - Genomes are significantly larger and more complex, containing up to billions of base pairs.
Universal Properties of All Living Cells:
- Structure: All cells possess a cytoplasmic membrane, cytoplasm, a DNA genome, and ribosomes.
- Metabolism: All cells take up environmental nutrients, transform them chemically, conserve metabolic energy, and expel waste products.
  - Catabolism: Enzymatic degradation of molecules to release energy and generate chemical building blocks.
  - Anabolism: Biosynthetic construction of complex macromolecules from simpler precursors.
  - Gene Expression: Transcription of DNA information into RNA, followed by ribosomal translation of RNA into functional proteins using enzymatic catalysts.
- Growth: Information from genomic DNA is converted into proteins that execute biochemical work, converting nutrients into new cellular material to form daughter cells.
- Evolution: Random mutations in DNA sequence introduce new phenotypic properties, promoting evolutionary adaptation. Phylogenetic relationships between species are reconstructed using comparative DNA sequence alignment.
Properties Exhibited by Some Cells:
- Differentiation: Formation of specialized cellular structures, such as endospores, to survive harsh environmental conditions.
- Communication: Intercellular signaling wherein cells release and respond to small chemical messengers.
- Motility: Self-propulsion executed by specialized structures such as flagella.
- Horizontal Gene Transfer: Non-genealogical exchange of genetic material between distinct cells.

Microbial Cell Structure

Properties of Microbial Cells

Cell Size, Morphology, and Surface Area Relationships

Metric Conversions: $1$ \text{ micrometer } (\mu m) = 10^{-6} $\text{ meter } (1/1,000,000$ \text{ meter}).
Size Ranges:
- Prokaryotic Cells: Range from $0.2$ \text{ }\mu m to over $600$ \text{ }\mu m in diameter/length. Most typical prokaryotic cells measure between $0.5$ \text{ }\mu m and $10$ \text{ }\mu m in length.
- Eukaryotic Cells: Typically range from $5$ \text{ }\mu m to $100$ \text{ }\mu m in diameter/length.
Cell Size and Volume Metrics Across Representative Bacterial Species:
- Thiomargarita namibiensis: Chemolithotroph (sulfur oxidizer), forms cocci in chains. Size: $750$ \text{ }\mu m diameter; Cell Volume: $200,000,000$ \text{ }\mu m^3 ( $100,000,000\times$ volume of E. coli). Average cell diameter is $\sim 200$ \text{ }\mu m.
- Epulopiscium fishelsoni: Chemoorganotroph, tapered rods. Size: $80$ \text{ }\mu m \times 600 $\text{ }\mu m; Cell Volume:$ 3,000,000 $\text{ }\mu m^3 ($ 1,500,000\times volume of *E. coli*).\n * *Beggiatoa* species: Chemolithotroph (sulfur oxidizer), filaments. Size: 50 $\text{ }\mu m \times 160$ \text{ }\mu m; Cell Volume: $1,000,000$ \text{ }\mu m^3 ( $500,000\times$ volume of E. coli).
- Achromatium oxaliferum: Chemolithotroph (sulfur oxidizer), cocci. Size: $35$ \text{ }\mu m \times 95 $\text{ }\mu m; Cell Volume:$ 80,000 $\text{ }\mu m^3 ($ 40,000\times volume of *E. coli*).\n * *Lyngbya majuscula:* Cyanobacterium, filaments. Size: 8 $\text{ }\mu m \times 80$ \text{ }\mu m; Cell Volume: $40,000$ \text{ }\mu m^3 ( $20,000\times$ volume of E. coli).
- Thiovulum majus: Chemolithotroph (sulfur oxidizer), cocci. Size: $18$ \text{ }\mu m diameter; Cell Volume: $3,000$ \text{ }\mu m^3 ( $1,500\times$ volume of E. coli).
- Staphylothermus marinus: Hyperthermophile (Archaea), irregular coccoid clusters. Size: $15$ \text{ }\mu m diameter; Cell Volume: $1,800$ \text{ }\mu m^3 ( $900\times$ volume of E. coli; average cell diameter is $\sim 1$ \text{ }\mu m).
- Magnetobacterium bavaricum: Magnetotactic bacterium, rods. Size: $2$ \text{ }\mu m \times 10 $\text{ }\mu m; Cell Volume:$ 30 $\text{ }\mu m^3 ($ 15\times volume of *E. coli*).\n * *Escherichia coli:* Chemoorganotroph, rods. Size: 1 $\text{ }\mu m \times 2$ \text{ }\mu m; Cell Volume: $2$ \text{ }\mu m^3 ( $1\times$ baseline volume).
- Pelagibacter ubique: Marine chemoorganotroph, small rods. Size: $0.2$ \text{ }\mu m \times 0.5 $\text{ }\mu m; Cell Volume:$ 0.014 $\text{ }\mu m^3 ($ 0.007\times volume of *E. coli*).\n * *Ultra-small bacteria:* Uncultured groundwater bacteria, variable morphology. Size:

Three-Domain Phylogenetic Tree of Life

Cultivation-Independent Analysis and Microbial Diversity Curve