BIO2107 Lecture 2

UNIVERSITY OF GUYANA

FACULTY OF NATURAL SCIENCES

DEPARTMENT OF BIOLOGY
BIO 2107: THE BIOLOGY OF MICROORGANISMS
LECTURE 2: MICROBIAL BIODIVERSITY

Instructor: Dr. Sabrina Dookie
Date: 3rd October, 2025

Microbial Biodiversity

  • Definition: Microbial biodiversity is defined as the variability among microorganisms.

  • Focus Areas of Microbial Biodiversity:

    • Understanding how different kinds of microorganisms arose.

    • Investigating the similarities and differences among microorganisms.

    • Examining the evolution of microbial cells.

  • Origin: The diversity of microorganisms we see today is the result of nearly 4 billion years of evolution.

  • Measurement of Diversity: Microbial diversity can be studied through several perspectives beyond phylogeny, including:

    • Cell size and morphology (shape)

    • Physiology

    • Motility

    • Mechanism of cell division

    • Pathogenicity

    • Developmental biology

    • Adaptation to environmental extremes

  • Concept: The metabolic versatility of prokaryotes allowed them to thrive in a variety of habitats suitable for life according to the laws of chemistry and physics.

Perspectives of Microbial Diversity

  • Measures of Microbial Biodiversity:

    • Morphology: Structure

    • Metabolic Ecology

    • Behavioral Evolution

Morphological Diversity

  • Microbes such as bacteria can be categorized by shape:

    • Cocci (spherical) - often occur in pairs or clusters.

    • Rods (bacilli) - cylindrical shape.

    • Spirilla (spiral) - twisted shape.

  • Other cell shapes include:

    • Filaments: Branched or unbranched structures.

    • Irregular shapes or Pleomorphic: Varied shapes depending on conditions.

    • Star-shaped, Stalked: Unique morphological examples.

    • Example: Haloquadratum is a flat, square microorganism.

Detailed Morphological Examples

  • Cell Morphologies:

    • Coccus: Diameter in photomicrograph - 1.5 μm

    • Rod: Diameter - 1 μm

    • Spirillum: Diameter - 1 μm

    • Spirochete: Diameter - 0.25 μm

    • Budding and appendaged: Diameter - 1.2 μm

    • Filamentous: Diameter - 0.8 μm

  • Multicellular Arrangements: Microbial cells can also exist in arrangements that exhibit multicellularity, including pairs, tetrads, filaments, and sheets.

    • Many species can form multi-species mats that resemble animal and plant tissues, enabling complex biochemical transformations.

  • Size Range: Most bacteria and archaea measure 1 to 5 μm, with some as small as 0.1 μm and others exceeding 1 mm.

Structural Diversity

  • Cell Envelopes in Bacteria:

    • Gram-positive: Characterized by a single membrane and a thick cell wall.

    • Gram-negative: Characterized by a double membrane and a thin cell wall.

    • Variants include:

    • Many gram-positives have outer membranes composed of mycolic acids.

    • Some gram-negatives lack the lipopolysaccharide layer.

  • S-Layer: Orderly protein coat present in many archaea and bacteria.

  • Peptidoglycan:

    • Fundamental component of bacterial cell walls.

    • Variations exist within types of peptidoglycan.

  • Archaeal Cell Walls: Lack peptidoglycan but may have pseudomurein.

  • Microbial Structures: Include flagella, pili, capsules, sheaths, and spores, illustrating a vast array of internal structures.

Metabolic Diversity

  • Energy Requirements: All cells need an energy source and a method to obtain and conserve energy.

  • Energy Sources:

    • Organic chemicals

    • Inorganic chemicals

    • Light

  • Classification Based on Energy Sources:

    • Chemotrophs: Organisms that obtain energy from chemicals.

    • Chemoorganotrophs: Organisms that utilize organic chemicals for energy conservation.

  • Energy Conservation: Energy from the oxidation of compounds is stored in adenosine triphosphate (ATP).

  • Aerobes vs. Anaerobes:

    • Aerobes: Require oxygen for energy.

    • Anaerobes: Depend on anoxic conditions for energy extraction.

Ecological Diversity

  • Habitat Range: Microbes inhabit various environments including:

    • Laboratory settings

    • Freshwater and marine environments

    • Extreme environments like the Great Salt Lake and the Dead Sea.

  • Temperature Tolerance: Microorganisms can survive in temperatures ranging from −5°C to over 118°C.

  • pH Levels: Some species thrive in environments with pH 0 (acidic conditions) and pH 11 (alkaline conditions).

  • Symbiosis: Many microbes form intimate relationships with other organisms, participating in complex ecosystems or residing as intracellular guests.

Behavioral Diversity

  • Mobility and Taxis:

    • Microbial movement varies, including phototactic behaviors in Chlorobium and chemotactic responses in Rhizobium.

  • Magnetotactic Bacteria: Possess magnetic orientation capabilities.

  • Developmental Cycles: All organisms exhibit growth cycles transitioning from active growth to resting states (e.g., log phase and stationary phase).

Specialized developmental cycles may involve sporulation or forming distinct cellular types (e.g., heterocysts in cyanobacteria).

  • Communal Behavior: Microbes often communicate through chemical signals and form complex structures such as fruiting bodies through cellular aggregation.

  • Community Formation: Microbes may form resource-recycling communities known as mats.

Evolutionary Diversity

  • Genetic Diversity: Serves as a foundation for microbial evolution, indicating that microbial organisms are significantly more diverse than macroscopic organisms.

  • Phylogenetic Trees: Represent the evolutionary relationships based on genetic data, showing lineages and divergence of organisms.

Other Major Groups of Microorganisms

Protists:

  1. Eukaryotic, single-celled microorganisms.

  2. Size: Ranges from 1 μm to 2,000 μm.

  3. Lack cell walls and exhibit various modes of movement.

  4. Amoebas use amoeboid movement for locomotion.

Viruses:

  1. Considered obligate parasites, not truly alive, replicating only within host cells.

  2. Absence of cellular structures like membranes and ribosomes.

  3. Economically significant with the diverse ability to affect cells across all domains of life.

Fungi:

  1. Eukaryotic organisms with rigid cell walls.

  2. Unicellular (yeasts) or multicellular (molds).

  3. Do not perform photosynthesis; absorb nutrients from the environment.

  4. Yeasts ferment carbohydrates for alcohol and CO2 production.

Origin of Life, Evolution, and Microbial Biodiversity

  • Fossil evidence suggests prokaryotic life existed 3.5 to 3.8 billion years ago based on stromatolite findings.

  • Key Events:

    • The maximum time for life's origin is aligned with Earth's formation.

    • Oxygenic photosynthesis originated around 2.4 billion years ago.

    • The oxygenation process happened gradually over approximately 2 billion years.

  • Hypotheses on Life's Origin:

    1. Surface Origin Hypothesis: Life began in a 'warm little pond', but conditions may have been too hostile.

    2. Subsurface Origin Hypothesis: Life likely originated at hydrothermal springs with stable conditions for biochemistry.

    • Key Elements: Thermal and chemical gradients offered energy and stability for life's emergence.

    • Organic compounds formed through interaction with mineral precipitates.

Steps Towards Cellular Life

  • Phospholipid vesicles eventually enclosed biochemical machinery, setting the stage for cellular evolution.

  • The last universal common ancestor (LUCA) reflects life evolution along different nutrient niches through early Bacteria and Archaea around 4 billion years ago.

RNA World and Evolution of Metabolism

  • Early life forms likely initiated as self-replicating RNAs, subsequently evolving into DNA-utilized organisms.

  • Metabolic diversity expanded on early Earth and led to significant oxygen-producing cyanobacteria.

The Endosymbiotic Theory

  • The evolution of eukaryotic cells through endosymbiotic events leading to mitochondria and chloroplasts is widely accepted.

  • Oxygen production played a critical role in expanding metabolic possibilities and enabling life to thrive on land.

Major Phylogenetic Groups:

  • Life organized into three primary domains: Bacteria, Archaea, and Eukarya.

  • Understanding features such as cell structure, membranes, and genetic elements will enhance comprehension of microbial diversity.