Core Concepts in Microbiology: Study Guide

Lecture 1: Introduction

Overview of Microbiology

Microbiology is the study of microscopic organisms, including bacteria, archaea, viruses, fungi, and protozoa. This field encompasses various disciplines and explores the diversity, classification, and roles of microbes in nature and human health.

• Disciplines of Microbiology: Includes bacteriology, virology, mycology, parasitology, and immunology.

• Relative Size of Microbes: Microbes vary in size; viruses are generally the smallest, followed by bacteria and eukaryotic microbes.

• Domains of Life: The three domains are Bacteria, Archaea, and Eukarya. Each has distinct cellular structures and genetic makeup.

• Distinguishing Features: Bacteria and archaea are prokaryotes (lack a nucleus), while eukaryotes have membrane-bound organelles.

• Taxonomy and Nomenclature: Scientific naming uses binomial nomenclature (Genus species), e.g., Escherichia coli.

• Historical Figures: Leeuwenhoek, Pasteur, Koch, Nightingale, Snow, Jenner, Lister, and Semmelweis made significant contributions to microbiology.

• Germ Theory of Disease: The concept that microorganisms cause disease, proven by Koch's postulates.

Lecture 2: Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

Microbial cells are classified as prokaryotic or eukaryotic based on their structural features. Understanding these differences is essential for studying microbial physiology and genetics.

• Compartmentalization: Eukaryotes have membrane-bound organelles; prokaryotes do not.

• Cellular Components: Eukaryotic cells contain a nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus. Prokaryotic cells have ribosomes, cell wall, and plasma membrane.

• Genetic Organization: Eukaryotes package DNA in chromosomes within the nucleus; prokaryotes have a nucleoid region.

• Structures in Eukaryotes: Organelles such as mitochondria and chloroplasts perform specialized functions.

• Bacterial Shapes: Common shapes include cocci (spherical), bacilli (rod-shaped), and spirilla (spiral).

• Endosymbiotic Theory: Explains the origin of mitochondria and chloroplasts as formerly free-living bacteria.

• Cell Envelope Structure: Gram-positive bacteria have thick peptidoglycan layers; Gram-negative bacteria have thin peptidoglycan and an outer membrane.

• External Structures: Flagella (motility), pili (attachment), and capsules (protection) are found in certain bacteria.

Lecture 3: Metabolism

Microbial Metabolic Pathways

Microbial metabolism includes all chemical reactions that provide energy and build cellular components. Key pathways include glycolysis, fermentation, respiration, and photosynthesis.

• Cellular Machinery: Enzymes, electron carriers, and ATP are central to metabolism.

• Energy Production: Glycolysis converts glucose to pyruvate; respiration uses the electron transport chain and chemiosmosis to generate ATP.

• Fermentation: Occurs in the absence of oxygen, producing products like lactic acid or ethanol.

• Aerobic vs. Anaerobic Respiration: Aerobic uses oxygen as the final electron acceptor; anaerobic uses other molecules.

• Fermentation Pathways: Bacteria utilize various fermentation pathways, such as lactic acid fermentation and alcoholic fermentation.

Equation for ATP Generation (Chemiosmosis):

$\text{ADP} + \text{P}_i \rightarrow \text{ATP}$

Lecture 4: Microbial Nutrition and Growth

Microbial Growth and Nutritional Requirements

Microorganisms require specific nutrients and environmental conditions for growth. Their metabolism and growth rates are influenced by energy sources, carbon sources, and physical factors.

• Nutritional Classifications: Phototrophs (light energy), chemotrophs (chemical energy), autotrophs (CO2 as carbon source), heterotrophs (organic carbon).

• Oxygen Requirements: Aerobes require oxygen; anaerobes do not. Facultative anaerobes can use either.

• Photosynthesis vs. Chemosynthesis: Photosynthetic organisms use light; chemosynthetic use inorganic chemicals.

• Bacterial Growth Curve: Four phases: lag, log (exponential), stationary, and death.

• Biofilms: Communities of microorganisms attached to surfaces, important in health and disease.

• Culture Media: Types include defined, complex, enriched, selective, and differential media.

• Environmental Factors: Temperature, osmolarity, hydrostatic pressure, and pH affect growth.

• Oxygen Toxicity: Some bacteria produce enzymes (e.g., catalase, superoxide dismutase) to neutralize toxic oxygen species.

Table: Bacterial Oxygen Requirements

Type	Oxygen Requirement	Protective Enzymes
Obligate Aerobe	Requires oxygen	Catalase, superoxide dismutase
Obligate Anaerobe	Cannot tolerate oxygen	None
Facultative Anaerobe	Can grow with or without oxygen	Catalase, superoxide dismutase
Microaerophile	Requires low oxygen	Some protective enzymes
Aerotolerant Anaerobe	Does not use oxygen but tolerates it	Superoxide dismutase

Table: Bacterial Growth Phases

Phase	Description
Lag	Adaptation to environment; no cell division
Log (Exponential)	Rapid cell division and population growth
Stationary	Growth rate slows; nutrients deplete
Death	Cells die due to lack of nutrients and accumulation of waste

Equation for Bacterial Growth:

$N_t = N_0 \times 2^n$

Where $N_t$ is the final number of cells, $N_0$ is the initial number, and $n$ is the number of generations.

Additional info: These notes expand on the syllabus outline by providing definitions, examples, and key equations relevant to each topic for comprehensive exam preparation.