Microbiology Study Guide: Nutrition, Metabolism, Genetics, and Microbial Physiology

Chapter 9: Microbial Nutrition and Physiology

Nutrition and Nutrients

Microorganisms require various nutrients for growth, maintenance, and reproduction. Understanding the types and sources of nutrients is fundamental in microbiology.

• Nutrition: The process by which organisms obtain and use nutrients for energy, growth, and maintenance.

• Essential Nutrient: A nutrient required for normal physiological function that cannot be synthesized by the organism and must be obtained from the environment.

• Macronutrients: Nutrients required in large amounts, such as carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S).

• Micronutrients (Trace Elements): Nutrients required in small amounts, often as enzyme cofactors (e.g., iron, zinc, copper).

• Organic vs. Inorganic: Organic nutrients contain carbon and hydrogen; inorganic nutrients do not.

Example: Glucose is an organic macronutrient, while magnesium is an inorganic micronutrient.

Reservoirs and Sources of Nutrients

Microbes obtain nutrients from various reservoirs in the environment.

• Major Reservoirs: Atmosphere (for gases), soil, water, and living organisms.

• Carbon Sources: Autotrophs use CO2; heterotrophs use organic compounds.

• Nitrogen Sources: Nitrogen gas (N2), ammonia (NH3), nitrate (NO3-), and organic nitrogen.

• Oxygen Sources: O2 from the atmosphere, water, and organic molecules.

• Hydrogen Sources: Water (H2O), organic compounds.

• Phosphorus Sources: Phosphate minerals, organic phosphates.

• Sulfur Sources: Sulfate (SO42-), sulfide, organic sulfur compounds.

Growth Factors and Energy Sources

Microbes may require specific organic compounds (growth factors) and obtain energy from various sources.

• Growth Factor: An organic compound (e.g., vitamin, amino acid) required for growth because the organism cannot synthesize it.

• Phototrophs: Use light as an energy source.

• Chemotrophs: Use chemical compounds as energy sources.

• Autotrophs vs. Heterotrophs: Autotrophs use CO2 as a carbon source; heterotrophs use organic carbon.

Transport Mechanisms

Microbes transport nutrients across membranes using various mechanisms.

• Passive Transport: Movement of substances down their concentration gradient (e.g., diffusion, osmosis).

• Active Transport: Movement against the gradient, requiring energy (e.g., pumps, group translocation).

• Facilitated Diffusion: Passive transport via membrane proteins.

Osmosis and Environmental Adaptations

Microbes adapt to different osmotic environments.

• Osmosis: Movement of water across a semipermeable membrane.

• Osmotolerant: Can survive in high solute concentrations.

• Halophiles: Thrive in high salt environments.

• Acidophiles/Alkaliphiles: Prefer acidic or alkaline pH.

Microbial Growth and Classification

Microbes are classified based on temperature, oxygen, and other requirements.

• Psychrophile: Optimal growth at low temperatures (0–15°C).

• Mesophile: Optimal growth at moderate temperatures (20–45°C).

• Thermophile: Optimal growth at high temperatures (45–80°C).

• Hyperthermophile: Optimal growth above 80°C.

• Aerobe: Requires oxygen.

• Anaerobe: Grows without oxygen.

• Facultative Anaerobe: Can grow with or without oxygen.

• Microaerophile: Requires low oxygen levels.

• Barophile: Thrives under high pressure.

Symbiotic Relationships

Microbes interact with other organisms in various symbiotic relationships.

• Mutualism: Both partners benefit.

• Commensalism: One benefits, the other is unaffected.

• Parasitism: One benefits at the expense of the other.

• Synergism: Cooperative interaction for enhanced effect.

• Antagonism: One organism inhibits another.

Microbial Growth Curve

Microbial populations grow in distinct phases.

• Lag Phase: Adaptation, no increase in cell number.

• Log (Exponential) Phase: Rapid cell division.

• Stationary Phase: Growth rate equals death rate.

• Death Phase: Decline in viable cells.

Methods of Enumerating Bacteria

Several methods are used to count bacteria.

• Direct Count: Microscopy or electronic counters.

• Viable Plate Count: Counting colonies on agar plates.

• Turbidity Measurement: Using spectrophotometry.

• Advantages: Direct counts are quick; plate counts measure only living cells.

Chapter 10: Microbial Metabolism

Metabolism, Catabolism, and Anabolism

Microbial metabolism includes all chemical reactions in the cell.

• Metabolism: Sum of all chemical reactions in a cell.

• Catabolism: Breakdown of molecules to release energy.

• Anabolism: Synthesis of complex molecules from simpler ones.

• Catabolic Reaction: Exergonic (releases energy).

• Anabolic Reaction: Endergonic (requires energy).

Enzymes and Their Properties

Enzymes are biological catalysts that speed up reactions.

• Enzyme: Protein that catalyzes biochemical reactions.

• Substrate: The molecule upon which an enzyme acts.

• Active Site: Region of enzyme where substrate binds.

• Apoenzyme: Protein portion of an enzyme.

• Cofactor: Non-protein component required for enzyme activity (e.g., metal ions).

• Coenzyme: Organic cofactor (e.g., NAD+, FAD).

• Constitutive Enzyme: Always present.

• Regulated Enzyme: Produced as needed.

Enzyme Classification and Mechanisms

• Oxidoreductases: Catalyze oxidation-reduction reactions.

• Transferases: Transfer functional groups.

• Hydrolases: Catalyze hydrolysis reactions.

• Lyases: Add or remove groups to form double bonds.

• Isomerases: Rearrange atoms within a molecule.

• Ligases: Join two molecules together.

Energy Production and ATP

ATP is the universal energy currency in cells.

• ATP (Adenosine Triphosphate): Stores and transfers energy.

• Substrate-Level Phosphorylation: Direct transfer of phosphate to ADP.

• Oxidative Phosphorylation: ATP generated via electron transport chain.

• Photophosphorylation: ATP generated using light energy.

Catabolic Pathways

• Glycolysis: Breakdown of glucose to pyruvate.

• Krebs Cycle: Oxidation of acetyl-CoA to CO2 and NADH.

• Electron Transport Chain: Series of redox reactions producing ATP.

• Fermentation: Anaerobic process producing ATP and organic acids/alcohols.

Equation for aerobic respiration:

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

Chapter 6: Microbial Genetics

Genetics and Genomes

Microbial genetics studies heredity and variation in microorganisms.

• Genetics: Study of heredity and variation.

• Gene: Segment of DNA coding for a protein or RNA.

• Genome: Complete set of genetic material in an organism.

• Genotype: Genetic makeup.

• Phenotype: Observable traits.

• Chromosome: DNA molecule containing genetic information.

• Prokaryotic Chromosome: Usually circular, single.

• Eukaryotic Chromosome: Linear, multiple.

Gene Expression and Protein Synthesis

• Transcription: Synthesis of RNA from DNA template.

• Translation: Synthesis of protein from mRNA template.

• mRNA: Messenger RNA, carries genetic code.

• tRNA: Transfer RNA, brings amino acids.

• rRNA: Ribosomal RNA, part of ribosome.

• Codon: Sequence of three nucleotides coding for an amino acid.

• Anticodon: tRNA sequence complementary to codon.

Mutation and Genetic Variation

• Mutation: Change in DNA sequence.

• Spontaneous Mutation: Occurs naturally.

• Induced Mutation: Caused by mutagens.

• Wild Type: Normal, non-mutated gene.

• Mutant: Organism with a mutation.

Genetic Recombination

• Transformation: Uptake of free DNA from environment.

• Transduction: Transfer of DNA by bacteriophage.

• Conjugation: Transfer of DNA via direct cell-to-cell contact.

Example: Griffith's experiment demonstrated transformation in Streptococcus pneumoniae.

Biotechnology and Genetic Engineering

• Bioengineered Pseudomonas species: Modified for bioremediation and other applications.

• Craig Venter: Pioneered synthetic genomics and creation of artificial life.

HTML Table: Classification of Microbes by Oxygen Requirement

Type	Oxygen Requirement	Example
Obligate Aerobe	Requires oxygen	Mycobacterium tuberculosis
Obligate Anaerobe	Cannot tolerate oxygen	Clostridium botulinum
Facultative Anaerobe	Can grow with or without oxygen	Escherichia coli
Microaerophile	Requires low oxygen	Helicobacter pylori
Aerotolerant Anaerobe	Does not use oxygen but tolerates it	Streptococcus pyogenes

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard microbiology curriculum.