Microbial Nutrition, Growth, Genetics, and Biotechnology: Study Guide

Microbial Metabolism Metabolism Overview Metabolism: All chemical reactions in a cell. Catabolism: Breakdown of molecules, releases energy. Anabolism: Synthesis of molecules, requires energy. ATP and Phosphorylation ATP: Main energy currency of the cell. Phosphorylation Types: Substrate-level, oxidative, photophosphorylation. Role of ATP: Couples energy-releasing and energy-consuming reactions. Oxidation-Reduction Reactions Oxidation: Loss of electrons. Reduction: Gain of electrons. Redox Reaction: Electron transfer from donor to acceptor. Enzymes and Enzyme Activity Enzyme: Biological catalyst, speeds up reactions. Substrate: Molecule acted upon by enzyme. Active Site: Region where substrate binds. Specificity: Enzymes act on specific substrates. Cofactor/Coenzyme: Non-protein helpers for enzyme activity. Activation Energy: Lowered by enzymes. Factors Affecting Activity: Temperature, pH, concentration. Inhibition: Competitive (blocks active site), noncompetitive (binds elsewhere). Carbohydrate Metabolism and Respiration Aerobic Respiration: Includes glycolysis, Krebs cycle, electron transport chain (ETC). Glycolysis: Glucose to pyruvate; produces ATP and NADH. Krebs Cycle: Oxidizes acetyl-CoA; produces NADH, FADH2, ATP, CO2. ETC: Transfers electrons to oxygen; generates ATP via oxidative phosphorylation. Electron Carriers: NADH, FADH2, cytochromes, ubiquinone. Chemiosmosis: Proton gradient drives ATP synthesis. Net Energy: Aerobic respiration yields more ATP than fermentation. Anaerobic Respiration: Uses other final electron acceptors (not O2). Fermentation: Incomplete oxidation; produces organic end products (e.g., lactic acid, ethanol). Fats/Proteins: Can be catabolized to enter glycolysis/Krebs cycle. Photosynthesis and Amphibolic Pathways Photosynthesis: Light-dependent (produces ATP, NADPH) and light-independent (Calvin cycle; fixes CO2) reactions. Products: Glucose, O2 (in oxygenic photosynthesis). Amphibolic Reactions: Pathways that function in both catabolism and anabolism. Additional info: For equations such as ATP production, glycolysis, and redox reactions, refer to standard biochemistry texts for detailed mechanisms and stoichiometry.

Microbial Nutrition and Growth

Nutritional Factors for Microbial Growth

Microorganisms require specific nutrients for growth, which can be categorized as major elements, trace elements, and growth factors.

• Major elements: Carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus are required in large amounts for cell structure and metabolism.

• Trace elements: Elements such as iron, copper, zinc, and manganese are needed in small quantities, often as enzyme cofactors.

• Growth factors: Organic compounds (e.g., vitamins, amino acids, nucleotides) that some microbes cannot synthesize and must obtain from the environment.

Example: Escherichia coli can synthesize most of its own growth factors, while Neisseria species require many supplied in the medium.

Oxygen Toxicity and Neutralization

Oxygen can be toxic due to the formation of reactive oxygen species (ROS) such as superoxide radicals, hydrogen peroxide, and hydroxyl radicals. Cells neutralize these using enzymes:

• Superoxide dismutase (SOD): Converts superoxide radicals to hydrogen peroxide.

• Catalase: Converts hydrogen peroxide to water and oxygen.

• Peroxidase: Reduces hydrogen peroxide to water using NADH.

Equation:

$2H_2O_2 \xrightarrow{catalase} 2H_2O + O_2$

Classification by Carbon and Energy Sources

Microorganisms are classified based on their sources of carbon and energy:

• Photoautotrophs: Use light for energy and CO2 as a carbon source (e.g., cyanobacteria).

• Chemoautotrophs: Use inorganic chemicals for energy and CO2 as a carbon source (e.g., nitrifying bacteria).

• Photoheterotrophs: Use light for energy and organic compounds for carbon (e.g., purple non-sulfur bacteria).

• Chemoheterotrophs: Use organic compounds for both energy and carbon (e.g., most bacteria, fungi, animals).

Oxygen Requirements

• Obligate aerobes: Require oxygen for growth.

• Facultative anaerobes: Can grow with or without oxygen but grow better with oxygen.

• Obligate anaerobes: Cannot tolerate oxygen and may be killed by it.

Temperature Classifications

• Psychrophiles: Grow best at 0–15°C; found in cold environments like Arctic lakes.

• Mesophiles: Grow best at 20–40°C; includes most human pathogens.

• Thermophiles: Grow best at 45–80°C; found in hot springs.

• Hyperthermophiles: Grow above 80°C; found in hydrothermal vents.

pH Preferences

• Acidophiles: Thrive at pH < 5.5; found in acidic hot springs.

• Neutrophiles: Grow best at pH 6.5–7.5; most human pathogens.

• Alkalinophiles: Grow best at pH > 8; found in alkaline lakes.

Osmotic Pressure and Salt Tolerance

High salt or sugar concentrations create hypertonic environments, causing water to leave microbial cells (plasmolysis), inhibiting growth. This is why salt and sugar are effective preservatives.

• Obligate halophiles: Require high salt concentrations (e.g., Halobacterium).

• Facultative halophiles: Tolerate high salt but do not require it (e.g., Staphylococcus aureus).

Quorum Sensing and Biofilms

Quorum sensing is a process where bacteria communicate using chemical signals to coordinate group behaviors, such as biofilm formation.

• Biofilms: Complex communities of microorganisms attached to surfaces, protected by an extracellular matrix.

Colony Formation

A colony is a visible mass of microbial cells arising from a single cell or group of cells. Colonies form when bacteria are spread on solid media and multiply.

Obtaining Pure Cultures

• Streak plate method: Involves spreading a sample over the surface of agar to isolate individual colonies.

• Pour plate method: Involves diluting a sample and mixing it with molten agar before pouring into a plate.

Types of Culture Media

• Defined (synthetic) media: Exact chemical composition is known.

• Complex media: Contains extracts and digests of yeasts, meat, or plants; composition varies.

Specialized Media

• Selective media: Inhibits unwanted microbes and supports desired ones.

• Differential media: Distinguishes between organisms based on metabolic reactions.

• Anaerobic media: Supports growth of anaerobes by removing oxygen.

• Enrichment media: Favors the growth of a particular microbe from a mixed culture.

Generation Time and Growth Calculations

Generation time is the time required for a cell to divide or a population to double.

Equation:

$N = N_0 \times 2^n$

Where $N$ = final cell number, $N_0$ = initial cell number, $n$ = number of generations.

Bacterial Growth Curve

Bacterial populations exhibit four major phases:

1. Lag phase: Cells adjust to environment; little or no cell division.

2. Log (exponential) phase: Rapid cell division; population doubles at constant rate.

3. Stationary phase: Growth rate slows; nutrients deplete, waste accumulates.

4. Death phase: Cells die at an exponential rate.

Measuring Microbial Growth

• Plate counts: Counting colonies on agar plates.

• Membrane filtration: Filtering a sample and counting colonies on a filter.

• Direct microscopic count: Counting cells under a microscope using a counting chamber.

• Turbidity: Measuring cloudiness of a culture with a spectrophotometer.

Microbial Genetics

Genetic Terminology

• Gene: A segment of DNA encoding a functional product.

• Plasmid: Small, circular DNA molecule independent of the chromosome.

• Chromosome: DNA molecule containing most of the genetic material.

• Genome: The complete set of genetic material in a cell.

DNA Structure and Function

• DNA is a double helix composed of nucleotides.

• Nucleotide components: Deoxyribose sugar, phosphate group, nitrogenous base (A, T, G, C).

DNA Replication

• DNA polymerase: Synthesizes new DNA strands.

• DNA ligase: Joins Okazaki fragments on the lagging strand.

• DNA helicase: Unwinds the DNA double helix.

• Primase: Synthesizes RNA primers.

Diagram: (Not shown; students should be able to draw the replication fork with labeled enzymes.)

Transcription and Translation

• Transcription: Synthesis of mRNA from DNA by RNA polymerase.

• Translation: Synthesis of protein from mRNA by ribosomes.

Flow of genetic information:

$DNA \xrightarrow{transcription} mRNA \xrightarrow{translation} Protein$

Genetic Code and Protein Synthesis

• Codon: Three-nucleotide sequence on mRNA specifying an amino acid.

• Anticodon: Three-nucleotide sequence on tRNA complementary to codon.

• Start codon: AUG (methionine); signals start of translation.

• Stop codons: UAA, UAG, UGA; signal end of translation.

• Ribosome: Site of protein synthesis; facilitates codon-anticodon pairing.

Diagram: (Not shown; students should be able to draw mRNA, ribosome, and tRNAs.)

Genotype vs. Phenotype

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable characteristics resulting from genotype.

Mutations

• Mutation: Permanent change in DNA sequence.

• Substitution mutation: One base is replaced by another.

• Frameshift mutation: Insertion or deletion of bases alters reading frame.

• Silent mutation: No change in amino acid sequence.

• Missense mutation: Changes one amino acid.

• Nonsense mutation: Creates a stop codon, truncating the protein.

Mutagens

• Mutagen: Agent that causes mutations (e.g., UV radiation, chemicals like nitrous acid).

Gene Transfer in Bacteria

• Transformation: Uptake of naked DNA from the environment (Griffith's experiment demonstrated this in Streptococcus pneumoniae).

• Conjugation: Transfer of DNA via direct cell-to-cell contact, often involving F plasmids.

• Transduction: Transfer of DNA by bacteriophages (viruses that infect bacteria).

F plasmids: Carry genes for conjugation (fertility); R plasmids carry antibiotic resistance genes.

Biotechnology and Recombinant DNA Technology

Key Definitions

• Biotechnology: Use of living organisms or their products for practical purposes.

• Genetic engineering: Direct manipulation of an organism's genes.

• Recombinant DNA technology: Techniques for combining DNA from different sources.

Plasmids and Vectors

• Plasmids: Useful as vectors for gene cloning due to their ability to replicate independently and carry foreign genes.

• Vector: DNA molecule used to carry foreign genetic material into a cell (e.g., plasmids, viruses).

Restriction Enzymes and DNA Ligase

• Restriction enzymes: Cut DNA at specific sequences, creating sticky or blunt ends.

• DNA ligase: Joins DNA fragments together.

Applications of Recombinant DNA Technology

• Production of insulin, growth hormones, vaccines.

• Gene therapy, genetically modified organisms (GMOs).

PCR and DNA Analysis

• PCR (Polymerase Chain Reaction): Amplifies specific DNA sequences rapidly.

• Southern blot and RFLP: Techniques for analyzing DNA fragments and patterns.

• DNA fingerprinting: Identifies individuals based on unique DNA patterns.

Genomics and Bioinformatics

• Genomics: Study of whole genomes.

• Bioinformatics: Use of computational tools to analyze genetic data.

Genetic Engineering and Transgenic Organisms

• Genetic engineering: Examples include Bt corn (insect resistance) and golden rice (vitamin A production).

• Transgenic organism: Organism with genes from another species; created by introducing foreign DNA.

CRISPR-Cas System

• CRISPR-Cas: Bacterial/archaeal immune system that uses RNA-guided nucleases to target foreign DNA.

• Gene editing: CRISPR-Cas can be engineered to cut specific DNA sequences, allowing targeted gene modification.

Type of Microbe	Temperature Range (°C)	Example Environment
Psychrophile	0–15	Arctic lakes
Mesophile	20–40	Human body
Thermophile	45–80	Hot springs
Hyperthermophile	>80	Hydrothermal vents

Type of Media	Purpose
Selective	Suppresses unwanted microbes, encourages desired ones
Differential	Distinguishes microbes by metabolic reactions
Anaerobic	Supports growth of anaerobes
Enrichment	Favors growth of a particular microbe

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