Microbiology Study Guide: Metabolism, Growth, Genetics, and Classification

Microbial Metabolism

Definitions and Key Concepts

Microbial metabolism encompasses all chemical reactions that occur within microorganisms to sustain life. It includes both catabolism (breaking down molecules for energy) and anabolism (building cellular components).

• Metabolism: The sum of all chemical reactions in a living organism.

• Catabolism: Energy-releasing processes that break down complex molecules.

• Anabolism: Energy-consuming processes that build complex molecules from simpler ones.

• Enzymes: Biological catalysts that speed up metabolic reactions; their activity is affected by temperature, pH, and substrate concentration.

Carbohydrate Catabolism

Microorganisms obtain energy through the breakdown of carbohydrates, primarily via aerobic and anaerobic respiration.

• Aerobic Respiration: Utilizes oxygen as the final electron acceptor.

• Anaerobic Respiration: Uses other molecules (e.g., nitrate, sulfate) as final electron acceptors.

• Glycolysis: Converts glucose to pyruvic acid, producing ATP and NADH.

• Krebs Cycle: Further oxidizes pyruvic acid, generating more ATP, NADH, and FADH2.

• Fermentation: Occurs when oxygen is absent; produces organic acids, alcohols, and gases.

Equation for aerobic respiration:

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$

Industrial Applications

• Microbial fermentation is used in the production of yogurt, cheese, alcohol, and other products.

• Bacteria are utilized in biotechnology to produce useful compounds.

Photosynthesis in Bacteria

Some bacteria can perform photosynthesis, converting light energy into chemical energy.

• Photoautotrophs: Use light as an energy source and CO2 as a carbon source.

• Photoheterotrophs: Use light for energy but require organic compounds for carbon.

• Chemotrophs: Obtain energy from chemical compounds.

Bacterial Growth

Definitions and Growth Requirements

Bacterial growth refers to an increase in the number of cells, not cell size. Growth is influenced by environmental and nutritional factors.

• Psychrophiles: Grow best at low temperatures.

• Mesophiles: Prefer moderate temperatures (20–45°C).

• Thermophiles: Thrive at high temperatures.

• Halophiles: Require high salt concentrations.

• Acidophiles: Grow in acidic environments.

• Obligate vs. Facultative: Obligate organisms require specific conditions; facultative organisms can adapt to varying conditions.

Physical and Chemical Requirements

• Temperature, pH, osmotic pressure, and oxygen availability affect growth.

• Nutrient requirements include sources of carbon, nitrogen, sulfur, phosphorus, and trace elements.

Media Types

• Defined Media: Exact chemical composition is known.

• Complex Media: Contains extracts and digests of natural sources; composition varies.

• Selective Media: Inhibits growth of some organisms while allowing others to grow.

• Differential Media: Distinguishes between different types of bacteria based on metabolic properties.

• Reducing Media: Used for growing anaerobic bacteria.

Bacterial Genetics

Genetic Material and Replication

Bacterial genetics studies the structure, function, and transmission of genetic information in bacteria.

• Chromosome: Most bacteria have a single, circular chromosome.

• Plasmids: Small, circular DNA molecules that replicate independently and often carry antibiotic resistance genes.

• DNA Replication: DNA polymerase synthesizes new strands; replication is semi-conservative.

Gene Expression and Regulation

• Transcription: DNA is transcribed into RNA.

• Translation: RNA is translated into proteins.

• Operon Model: Explains gene regulation via repression and induction.

Genetic Recombination

• Transformation: Uptake of naked DNA from the environment.

• Conjugation: Transfer of DNA between bacteria via direct contact.

• Transduction: Transfer of DNA by bacteriophages.

• Transposons: Segments of DNA that can move within the genome; important for genetic diversity.

Prokaryotic Classification

Taxonomy and Major Groups

Prokaryotes are classified based on genetic, biochemical, and morphological characteristics.

• Proteobacteria: Includes Alpha, Beta, Gamma, Delta, and Epsilon subgroups.

• Non-proteobacteria: Includes Cyanobacteria, Chlamydiae, Chlorobi, Chloroflexi, Planctomycetes, Bacteroidetes, Fusobacteria, Spirochaetes.

• Gram-positive bacteria: Includes Bacillus, Mycoplasmatales, Actinomycetota, Deinococci.

Identification Methods

• Biochemical Tests: Assess metabolic capabilities (e.g., fermentation, enzyme activity).

• Serological Tests: Use antibodies to detect specific bacterial antigens.

• Genotypic Tests: PCR (Polymerase Chain Reaction) is used for rapid identification.

• Dichotomous Key: A tool for identifying organisms based on a series of choices.

• Bergey's Manual: Reference guide for bacterial classification.

Table: Major Bacterial Groups and Characteristics

Group	Main Characteristics	Examples
Proteobacteria	Gram-negative, diverse metabolism	Escherichia, Salmonella
Cyanobacteria	Photosynthetic, oxygenic	Anabaena, Nostoc
Firmicutes	Gram-positive, spore-forming	Bacillus, Clostridium
Actinobacteria	Gram-positive, high G+C content	Streptomyces, Mycobacterium
Spirochaetes	Spiral-shaped, motile	Treponema, Borrelia

Examples and Applications

• Extreme Thermophiles: Thrive in hot environments (e.g., hot springs).

• Halophiles: Adapted to high salt concentrations (e.g., salt lakes).

• Acidophiles: Grow in acidic conditions (e.g., acid mine drainage).

Additional info: Some context and definitions were expanded for clarity and completeness based on standard microbiology curriculum.