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