Microbial Cell Structure and Function: Study Notes

2.6 Cell Surface Structures

Capsules and Slime Layers

Capsules and slime layers are sticky polysaccharide coats outside the cell envelope, found in many bacteria. These structures play a crucial role in microbial survival and pathogenicity.

• Capsule: A tightly attached, dense matrix, visible under special stains, that protects bacteria from phagocytosis and desiccation.

• Slime Layer: A loosely attached, easily deformed layer, often washed away during sample preparation.

Capsules and slime layers assist in attachment to surfaces, contribute to infectivity, and prevent dehydration/desiccation.

Fimbriae and Pili

Fimbriae are short, hair-like appendages that mediate attachment to surfaces, while pili are longer, filamentous structures that can conduct electrons and facilitate motility.

2.7 Cell Inclusions

Energy Reserves and Storage Polymers

Cell inclusions are specialized structures that store energy and nutrients for microbial cells. These include:

• Glycogen: A glucose polymer that stores energy for microbial cells.

• Polyphosphate: A polymer of phosphate groups that stores energy for microbial cells.

Cell inclusions are enclosed by a thin protein membrane, which reduces osmotic stress and allows for efficient storage and utilization of energy.

2.8 Endospores

Endospore Formation and Germination

Endospores are specialized, dormant cells that are resistant to heat, radiation, and chemical exposure. They are formed by the differentiation of vegetative cells and are ideal for dispersal via wind, water, or animal gut.

• Endospore: A highly differentiated, dormant cell that is resistant to heat, radiation, and chemical exposure.

Endospores are present only in some gram-positive bacteria, such as Bacillus and Clostridium.

2.9 Flagella, Archaella, and Swimming Motility

Flagella and Archaella

Flagella and archaella are specialized structures that assist in swimming motility. They are present in both bacteria and archaea, and are responsible for the movement of cells and the formation of biofilms.

• Flagella: A long, thin appendage that assists in swimming motility.

• Archaella: A short, thick appendage that assists in swimming motility.

Flagella and archaella are present in both bacteria and archaea, and are responsible for the movement of cells and the formation of biofilms.

2.10 Chemotaxis

Measuring Chemotaxis

Chemotaxis is the directed movement of cells in response to chemical or physical stimuli. It is measured by inserting a capillary tube containing an attractant or a repellent in a suspension of motile bacteria.

2.13 The Nucleus and Cell Division

Nucleus and Cell Division

The nucleus is the central organelle of the cell, containing the chromosomes and responsible for cell division. It is present in both bacteria and archaea.

2.14 Mitochondria and Chloroplasts

Mitochondria and Chloroplasts

Mitochondria and chloroplasts are specialized organelles that are responsible for energy metabolism and photosynthesis. They are present in both bacteria and archaea.

2.15 Other Eukaryotic Cell Structures

Other Eukaryotic Cell Structures

Other eukaryotic cell structures include the cytoskeleton, endoplasmic reticulum, Golgi complex, and lysosomes. These structures are responsible for maintaining cell shape and position, and for the synthesis of proteins and other molecules.