Bacterial Cell Structure and Microbial Metabolism Essentials

Mycolic Acids

Mycolic acids are beta-hydroxy acids with branched, very long chains. They form a unique component of the bacterial cell wall skeleton, specifically associated with peptidoglycan (PG) and arabinogalactan.

Properties Conferred by the Cell Wall (AFB)

• Appearance: Waxy consistency of colonies in Petri dishes.
• Liquid Growth: Forms clumps in liquid media.
• Waterproofing: Provides high resistance to desiccation and antibacterial agents, including detergents, oxidants, acids, and bases.

Cellular Components

Nucleoid

Represented by the bacterium's chromosome, consisting of circular, single-stranded DNA.

Plasmid

Extrachromosomal genetic elements (DNA) with self-replicating capacity.

Spore

Spherical or ovoid refractile structures included within the vegetative cell. Composed of calcium and dipicolinic acid, which confer high resistance to harsh conditions. They can be disfiguring or deforming to the cell.

Flagella

Long, helical extracellular filaments consisting of flagellin. They act as antigens (flagellar antigen or "H"). Types include:

• Lophotrichous
• Peritrichous
• Monotrichous

Fimbriae

Straight, rigid filamentous appendages that are shorter and thinner than flagella, composed of pilin. There are two main types of pili: adhesive and sexual.

Microbial Physiology

Reproduction

Reproduction occurs by bipartition or fission, where one stem cell gives rise to two identical daughter cells. The time required to form two cells from one is called the generation time, which can range from minutes to days.

Microbial Nutrition

Includes autotrophy and heterotrophy, utilizing macronutrients and micronutrients, universal and particular nutrients, nitrogen fixation, and growth factors.

Metabolic Energy Concepts

Phototrophy (Light Energy)

• Photolithotrophy: Capturing light energy for nutrition using inorganic substances.
• Photoorganotrophy: Capturing light energy using organic substances.

Chemotrophy (Chemical Energy)

• Chemolithotrophy: Chemical energy derived from inorganic substances.
• Chemoorganotrophy: Chemical energy derived from organic substances.

Types of Fermentation and Products

• Lactic Fermentation: Produces lactic acid.
• Alcoholic Fermentation: Produces ethanol and CO₂.
• Mixed Acid Fermentation: Produces ethanol, succinic, acetic, formic, and lactic acids, plus CO₂ and H₂.
• Butylene Glycol Fermentation: Produces butylene glycol and CO₂.
• Acetone-Butyric Fermentation: Produces acetic acid, acetone, butyric acid, butanol, CO₂, and H₂.