Microbial Genetics, Biotechnology, and Classification: Study Notes

Chapter 8: Microbial Genetics

Mechanisms of Genetic Change

Microorganisms can acquire new genetic traits through several mechanisms, leading to genetic diversity and adaptation. The main mechanisms include mutation, transformation, transduction, and conjugation.

• Mutation: A mutation is a heritable change in the nucleotide sequence of an organism's DNA. Mutations can be spontaneous or induced by mutagens (e.g., chemicals, radiation).

• Transformation: Transformation is the uptake of naked DNA fragments from the environment by a bacterial cell. The incorporated DNA may recombine with the host genome, leading to genetic change.

• Transduction: In transduction, bacterial DNA is transferred from one cell to another by a bacteriophage (virus that infects bacteria). There are two types: generalized and specialized transduction.

• Conjugation: Conjugation involves the direct transfer of DNA from one bacterial cell to another via cell-to-cell contact, typically mediated by a pilus. Plasmids, such as the F (fertility) plasmid, are often transferred this way.

Example: Streptococcus pneumoniae can acquire genes for capsule formation via transformation, increasing its virulence.

Chapter 9: Biotechnology and DNA Technology

Restriction Enzymes and Plasmid Cutting

Restriction enzymes are molecular scissors that recognize specific DNA sequences and cut DNA at or near these sites. They are essential tools in genetic engineering.

• Restriction Enzyme: An enzyme that cleaves DNA at specific nucleotide sequences, producing defined fragments.

• Cutting Plasmids: Plasmids are circular DNA molecules used as vectors. Restriction enzymes can cut both plasmid and foreign DNA, allowing insertion of new genes.

Example: EcoRI recognizes the sequence GAATTC and cuts between G and A.

DNA Fingerprinting

DNA fingerprinting is a technique used to identify individuals or organisms based on unique patterns in their DNA.

• Process: DNA is cut with restriction enzymes, separated by gel electrophoresis, and visualized to compare banding patterns.

• Interpretation: Similar banding patterns suggest genetic relatedness; differences indicate genetic variation.

Biotechnology and Recombinant DNA

Biotechnology involves the use of living organisms or their products to modify or make products for specific uses. Recombinant DNA technology allows for the manipulation and transfer of genes between organisms.

• Definition: Biotechnology is the application of biological systems or organisms to technical and industrial processes.

• Transforming with Recombinant Plasmid: A recombinant plasmid contains foreign DNA inserted into a vector. Bacteria can be transformed with this plasmid to express new traits.

• Selectable Markers: Genes (e.g., antibiotic resistance) on the plasmid allow for selection of successfully transformed cells.

Example: Inserting the gene for human insulin into Escherichia coli allows the bacteria to produce insulin for medical use.

Steps for Constructing a Genomic Library

A genomic library is a collection of DNA fragments that represent the entire genome of an organism, stored in vectors for study or manipulation.

1. Isolate genomic DNA from the organism.

2. Cut the DNA into fragments using restriction enzymes.

3. Insert the fragments into vectors (e.g., plasmids, phages).

4. Introduce the vectors into host cells (e.g., bacteria).

5. Screen the library for clones containing genes of interest.

Steps for PCR (Polymerase Chain Reaction)

PCR is a technique used to amplify specific DNA sequences rapidly and efficiently.

1. Denaturation: Heat the DNA to separate strands.

2. Annealing: Cool to allow primers to bind to target sequences.

3. Extension: DNA polymerase synthesizes new DNA strands from the primers.

4. Repeat the cycle (typically 25-35 times) to exponentially amplify the target DNA.

Equation:

$\text{Number of DNA copies after n cycles} = 2^n$

Gene Silencing

Gene silencing refers to techniques that prevent the expression of specific genes, often using RNA interference (RNAi).

• Mechanism: Small interfering RNAs (siRNAs) bind to mRNA, leading to its degradation and preventing translation.

• Applications: Used in research and medicine to study gene function or treat diseases by silencing harmful genes.

Ethics of Bioengineering

Bioengineering raises important ethical questions regarding safety, environmental impact, and societal consequences.

• Concerns: Potential for unintended effects, gene flow to wild populations, and ethical considerations in modifying organisms.

• Regulation: Oversight by governmental and international bodies to ensure responsible use of biotechnology.

Chapter 10: Classification of Microorganisms

Domains: Bacteria and Archaea

Microorganisms are classified into three domains: Bacteria, Archaea, and Eukarya. This classification is based on differences in cell structure, genetics, and biochemistry.

• Bacteria: Prokaryotic, cell walls contain peptidoglycan, diverse metabolic pathways, found in many environments.

• Archaea: Prokaryotic, cell walls lack peptidoglycan, unique membrane lipids, often found in extreme environments (e.g., hot springs, salt lakes).

• Eukarya: Includes all eukaryotic organisms (not detailed in this section).

Evidence for Classification

Classification is supported by molecular, biochemical, and morphological evidence.

• Ribosomal RNA (rRNA) Sequencing: Comparison of 16S rRNA sequences reveals evolutionary relationships.

• Biochemical Tests: Assess metabolic capabilities and chemical composition.

• Morphology: Cell shape, structure, and staining characteristics.

Domain	Cell Type	Cell Wall	Membrane Lipids	Typical Habitats
Bacteria	Prokaryotic	Peptidoglycan	Ester-linked	Soil, water, living hosts
Archaea	Prokaryotic	No peptidoglycan	Ether-linked	Extreme environments

Additional info: Eukarya is the third domain, including fungi, protozoa, algae, and plants/animals, but is not detailed in the provided notes.