Biology of Microbial Cells Lecture 1

Biology of Microbial Cell

• Microbiology is the study of very small living organisms, known as microorganisms or microbes, which require a microscope to be seen.
• Microorganisms include bacteria, algae, protozoa, fungi, and viruses, with only 3% of them being pathogenic (disease-causing).

History of Microbiology

• The concept of microorganisms was first suggested by Antony Van Leeuwenhock, who discovered "animalcules".
• The Golden Age of Microbiology was marked by Louis Pasteur's work, which showed that microbes caused fermentation and spoilage, and disproved spontaneous generation.
• Pasteur also developed aseptic techniques, which involved removing pathogenic microorganisms from the environment.

Microbiology and Medicine

• The Germ Theory of Disease states that diseases are transmitted by microorganisms from a diseased person to a healthy person.
• Examples of diseases caused by specific microorganisms include Diphtheria (Corynebacterium diphtheriae) and Tetanus (Clostridium tetani).
• Robert Koch developed solid growth media, pure culture techniques, and aseptic lab techniques, and isolated bacteria as causative agents for Anthrax.

Koch's Postulates

• Koch's Postulates are a series of experimental steps to show that a specific organism causes a specific disease.

Spores and Sterilization

• Ferdinand Cohn discovered and described endospores, and the term "sterile" was introduced to mean the complete removal of all life forms, including endospores.

Microbiology Branches

• Basic Microbiology: classifications, metabolism, nutrition, growth, and requirements.
• Medical Microbiology: human pathogens.
• Industrial Microbiology: microorganisms used to obtain industrial products.
• Pharmaceutical Microbiology: production of drugs, enzymes, and solvents using microorganisms.
• Agricultural Microbiology: microorganisms used as biofertilizers and biocontrol agents of plant pathogens.
• Environmental Microbiology: microbial ecology, pollution, and biodegradation of toxic chemicals.

Classification

• Systematic biology provides scientific names, descriptions, and classifications for organisms.
• Aristotle divided the living world into two kingdoms: plants and animals, which persisted for over 2000 years.
• By the 19th century, a third kingdom, Protista, was added to accommodate microorganisms.

Cell Wall of Bacteria

• The cell wall is responsible for the shape of the cell, protects the interior structure, and prevents bacterial cells from rupturing due to osmotic pressure.
• The cell wall is composed of peptidoglycan, a polymer consisting of sugars and amino acids.
• Peptidoglycan can be destroyed by agents such as lysozyme, an enzyme that breaks the β-1,4-glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acid.

Gram-Positive and Gram-Negative Cell Walls

• Gram-positive bacteria have a thick cell wall consisting of several layers of peptidoglycan, with teichoic acids embedded in the cell wall.
• Gram-negative bacteria have a thin cell wall consisting of peptidoglycan, with a lipopolysaccharide layer (LPS) in the outer membrane.
• LPS is composed of polysaccharide, lipid A, and O-polysaccharide (O antigen), and is responsible for the pathogenicity of Gram-negative bacteria.

Periplasm

• The periplasm is a region between the outer surface of the cytoplasmic membrane and the inner surface of the outer membrane, about 15 nm wide.
• The periplasm contains proteins that are present outside the cytoplasmic membrane, but are kept from diffusing away by the outer membrane.