bio2107 lec 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

Definitions of Microbial Biodiversity

• Microbial biodiversity: Defined as the variability among microorganisms.
  • Focus on:
  • The origins of different kinds of microorganisms.
  • Similarities and differences among microorganisms.
  • Evolution of microbial cells.
  • Result of nearly 4 billion years of evolution.
• Microbial diversity can be characterized by several aspects:
  • Phylogeny
  • Cell size and morphology (shape)
  • Physiology
  • Motility
  • Mechanisms of cell division
  • Pathogenicity
  • Developmental biology
  • Adaptation to environmental extremes

Perspectives of Microbial Diversity

• Discusses different measures of microbial biodiversity, categorized into:
  • Morphology
  • Structure
  • Metabolic diversity
  • Ecology
  • Behavioural aspects
  • Evolutionary processes

Morphological Diversity

• Microbial cells are often categorized by shape:
  • Rods (bacilli)
  • Cocci (spherical)
  • Spirals (spirilla, spirochetes)
• Other bacterial and archaeal shapes include:
  • Filaments (branched or unbranched)
  • Irregular forms
  • Pleomorphic (forms can vary under different conditions)
  • Star-shaped and stalked
  • Example: Haloquadratum is a flat, square organism.
• Cell size range is generally between 1 to 5 μm, with extremes of 0.1 μm up to over 1 mm.

Structural Diversity

• Gram-positive vs. Gram-negative bacteria:
  • Gram-positive: Single membrane, thick cell wall.
  • Gram-negative: Double membrane, thin cell wall.
• Variations including:
  • Mycolic acids outer membrane in some Gram-positive bacteria.
  • Presence of lipopolysaccharide layer in Gram-negative bacteria.
• Common structural features across archaea and bacteria:
  • S-layer proteins
  • Peptidoglycan in bacterial cell walls; archaea have pseudomurein instead.
  • Variability in external structures such as flagella, pili, capsules, etc.
  • Internal structures include spores, daughter cells, thylakoids, mesosomes, and nucleoids.

Metabolic Diversity

• Cells must derive energy to fuel life processes.
• Energy sources in nature:
  • Organic chemicals
  • Inorganic chemicals
  • Light
• Types of microorganisms based on energy use:
  • Chemotrophs: Organisms that derive energy from chemical reactions.
  • Chemoorganotrophs: Organisms that specifically use organic chemicals.
• Energy storage:
  • Energy is conserved in the form of ATP (adenosine triphosphate).
• Aerobes rely on oxygen for energy; anaerobes thrive in its absence.

Ecological Diversity

• Microorganisms inhabit diverse environments:
  • Laboratory to natural ecosystems (freshwater, marine, etc.).
  • Adapted to extreme conditions (brines, pH levels ranging from 0 to 11, temperature extremes from −5°C to over 118°C).
• Many microbes establish symbiotic relationships, forming complex communities.

Behavioural Diversity

• Motility: Microbes exhibit various movements, such as:
  • Phototaxis (e.g., Chlorobium)
  • Chemotaxis (e.g., Rhizobium)
  • Magnetotaxis : Using the Earth’s magnetic field for navigation.
• Developmental stages include:
  • Active-growth (log phase) vs. resting (stationary phase)
  • Sporulation, cyst formation, and differentiation into distinct cell types.
• Communal behaviour:
  • Communication via chemical signals, triggering aggregation and community behaviour (e.g., Myxococcus formation).
  • Community mats recycling resources.

Evolutionary Diversity

• Genetic diversity serves as the foundation for evolutionary diversity.
• Microbial diversity mirrors biological diversity, highlighting the significance of unicellular organisms in evolutionary discussions.
• Evolutionary relationships represented through genealogical trees indicating genetic divergence.

Other Major Groups of Microorganisms

Protists

1. Single-celled, eukaryotic microorganisms (1 μm to 2,000 μm).
2. Protozoa: Cell structures typical of animal cells, can be motile, some are photosynthetic.
3. Amoeboid movement via pseudopods for locomotion.

Viruses

1. Obligate parasites, not considered alive; replicate within host cells.
2. Lack cellular structures like membranes and ribosomes; cannot conserve energy independently.
3. Genomes may consist of DNA or RNA, might be single or double-stranded.
4. Bacteriophages: Viruses that infect bacteria, used in research.

Fungi

1. Eukaryotic, rigid cell walls, can be unicellular or multicellular.
2. Cannot carry out photosynthesis; absorb dissolved nutrients.
3. Hyphae form multicellular structures known as mycelium; yeasts are unicellular.
4. Yeasts can ferment sugars producing alcohol and CO2.

Origin of Life and Evolution of Microbial Biodiversity

• First fossilized prokaryotic cells dated to 3.5-3.8 billion years old, found in stromatolites.
• Evidence suggests microbial life emerged shortly after Earth's formation with diverse forms present early on.
• Oxygenic photosynthesis: Originated around 2.4 billion years ago during the Great Oxidation Event; oxygen accumulation in the atmosphere was gradual.

Hypotheses on the Origin of Life

Surface Origin Hypothesis

• Suggests life began in a primordial soup on Earth's surface, but conditions were likely hostile.

Subsurface Origin Hypothesis

• Proposes life began at hydrothermal springs, conditions being much less hostile.
• Reduced inorganic compounds provided stable energy.
• Precipitates formed structured mounds serving as energy-rich compartments for early life.

Phospholipid Membrane Vesicles

• Key for enclosing biochemical machinery, might have encapsulated RNA/DNA leading to the first self-replicating cells.
• LUCA: Last Universal Common Ancestor, from which Bacteria and Archaea diverged.

RNA World and Protein Synthesis

• Suggests first self-replicating organisms may have been RNA-based.
• Evolution of DNA came later alongside protein synthesis.
• Early metabolism was anaerobic and chemolithotrophic.

Divergence of Bacteria and Archaea

• By around 2 billion years ago, cells began evolving complex structures leading to eukaryotes.
• Endosymbiotic theory explains the origins of mitochondria and chloroplasts:
  • Mitochondria from aerobic bacteria; chloroplasts from cyanobacterial descent.

Endosymbiotic Theory

• Infoldings in ancestral prokaryotic membranes led to the emergence of nucleus/organelles.
• Oxygen produced via photosynthesis was pivotal in the evolution of aerobic respiration.

Evolutionary Development of Eukaryotes

• The earliest eukaryotes arose approximately 2 billion years ago from endosymbiotic events.
• Endosymbiotic events led to significant evolutionary milestones; all eukaryotes are derived from this union of different organisms.

Microbial Evolution and Genomic Changes

• Evolution involves descent with modification; mutation and selection drive genetic diversity.
• DNA changes come from mutations and horizontal gene transfer, essential for microbial evolution.

Phylogenetic Analysis

• Phylogenetic trees depict evolutionary relationships based on genetic data, revealing common ancestry
• Cladistics: A modern method for tree construction based on nucleotide changes, often examining 16S rRNA sequences.

Implications of Phylogenetic Analysis

• Revealed life on Earth consists of three primary domains:
  • Bacteria
  • Archaea
  • Eukarya (including plants, animals, fungi)

Key Characteristics of Microbial Domains

Conclusion

• The study of microbial biodiversity encompasses diverse themes including morphological, structural, metabolic, ecological, behavioral, and evolutionary aspects, shaping our understanding of life’s origins and evolutionary processes.