05. ORGANISMS OF MICROBIAL WORLD

Organisms That Make Up The Microbial World

• Introduction to the major categories of microorganisms

Topic Learning Objectives

• Define and describe the structural and functional features common to microbes

• Identify major eukaryotic microbes in terms of morphology, physiology, habitat, and pathogenicity

• Compare prokaryotic domains: Bacteria and Archaea

• Understand the pathogenicity of viruses

Major Characteristics of Microorganisms

Morphological / Structural

• Characteristics include:

  • Cell shape and arrangement

  • Size

  • Special structures and developmental forms

Chemical

• Various chemical constituents that compose microbial cells

• Known example: Structure of Human Immunodeficiency Virus (HIV) includes glycoproteins, lipid membrane, RNA, capsid, matrix, reverse transcriptase

Cultural

• Nutritional requirements

• Physical conditions for growth: temperature and pH

• Classification of microorganisms by their temperature preferences:

  • Psychrophiles (e.g., Pseudomonas)

  • Mesophiles (e.g., Staphylococcus aureus, E. coli)

  • Thermophiles (e.g., Thermus aquaticus)

Metabolic

• Types of Metabolism:

  • Phototrophic: organisms that obtain energy from light (e.g., Rhodospirillum)

  • Chemotrophic: organisms that make their own energy using chemical energy (e.g., Archaebacteria)

Antigenic

• Distinctive antigens that may include:

  • Capsule (K antigen in Salmonella)

  • Somatic (O antigen, cell wall antigen)

  • Flagellar (H antigen)

Atmospheric Requirements

• Oxygen relationships and requirements:

  • Obligate Anaerobes (do not require O₂)

  • Facultative Anaerobes (can grow with or without O₂)

  • Obligate Aerobes (require O₂)

  • Microaerophiles (require reduced O₂ levels)

  • Capnophiles (grow better in increased CO₂)

Genetic

• Distinctive hereditary materials such as nucleoproteins (RNA)

Pathogenicity

• Ability to cause disease:

  • Examples include:

    • Group A Streptococcus (strep throat)

    • Salmonella (food poisoning)

    • Influenza virus (flu)

Ecological

• Distribution and interaction of microorganisms in nature

Eukaryotic Microbes

Types

• Eukaryotes include:

  • Algae

  • Fungi

  • Lichens

  • Slime molds

Algae

Characteristics

• Photosynthetic

• Diverse morphology: microscopic (unicellular) to macroscopic (multicellular)

Morphology

• Varied structure including chloroplasts, nucleus, and cell wall

Habitats

• Aquatic environments (marine and freshwater) and terrestrial environments

Pathogenicity

• Examples include:

  • Paralytic shellfish poisoning caused by dinoflagellates

  • Ciguatera poisoning from specific fish

Fungi

Characteristics

• Non-photosynthetic; lack chlorophyll

• Composed of chitin in cell walls

Morphology

• Divided into macroscopic (e.g., mushrooms) and microscopic (e.g., molds, yeasts)

Importance

• Decomposers, food sources, and production of antibiotics

Viruses

Characteristics

• The smallest known organisms, acellular infectious agents

• Obligate intracellular parasites

Morphology

• Bacteriophages and viral structure

• Participate in a complex life cycle including:

  • Attachment, penetration, uncoating, synthesis, assembly, release

Pathogenicity

• Cause many diseases (e.g., rabies, influenza)

Importance

• Vaccines, genetic engineering, and drug development