Microbial Genetics, Classification, Viruses, and Eukaryotic Microorganisms: Study Notes

Microbial Genetics

Genetic Material and Processes

Microbial genetics explores the structure, function, and transmission of genetic material in microorganisms. Understanding these processes is essential for grasping how microbes evolve, adapt, and cause disease.

• Genome: The complete set of genetic material in an organism, including all genes and non-coding sequences.

• Gene: A segment of DNA that encodes a functional product, usually a protein.

• Chromosome: A DNA molecule with part or all of the genetic material of an organism.

• STRs (Short Tandem Repeats): Repeated sequences of DNA that are useful in genetic fingerprinting.

• Purines and Pyrimidines: Nitrogenous bases in DNA and RNA. Purines (A, G), Pyrimidines (C, T, U).

• Complementarity: The property that allows bases to pair (A-T, G-C in DNA).

Replication, Transcription, and Translation

• Replication: The process by which DNA is copied before cell division. Key enzymes include DNA polymerase, helicase, ligase, and primase.

• Transcription: The synthesis of RNA from a DNA template, involving RNA polymerase.

• Translation: The process by which ribosomes synthesize proteins using mRNA as a template.

Key Enzymes: DNA/RNA polymerases, helicase, ligase, topoisomerase, exonucleases, endonucleases.

Key Molecules: mRNA, tRNA, rRNA, snRNA, microRNA.

Gene Regulation

• Promoter: DNA sequence where RNA polymerase binds to initiate transcription.

• Operator: Segment of DNA to which a repressor binds, regulating gene expression.

• Repressor/Activator: Proteins that decrease/increase transcription rates.

• Inducer/Corepressor: Molecules that modulate the activity of repressors/activators.

• Operon: A cluster of genes under control of a single promoter (e.g., lac operon).

Plasmids and Gene Exchange

• Plasmid: Small, circular DNA molecule independent of chromosomal DNA, often carrying antibiotic resistance genes.

• Conjugation: Transfer of genetic material between bacteria via direct contact.

• Transformation: Uptake of free DNA from the environment.

• Transduction: Transfer of DNA via bacteriophages.

Example: The lac operon in Escherichia coli regulates lactose metabolism and is a classic model of gene regulation.

Additional info: PCR (Polymerase Chain Reaction) is a technique used to amplify DNA sequences for analysis.

Microbial Classification

Taxonomy and Systematics

Microbial classification organizes microorganisms into groups based on shared characteristics. This helps in identification, understanding evolutionary relationships, and predicting behavior.

• Taxonomy: The science of classification, including identification, nomenclature, and grouping.

• Hierarchy: Domain, Phylum, Class, Order, Family, Genus, Species.

• Major Groups: Bacteria, Archaea, Eukarya (including fungi, protozoa, algae).

Examples of Bacterial Genera

• Gram-positive: Staphylococcus, Streptococcus, Bacillus, Clostridium

• Gram-negative: Escherichia, Salmonella, Shigella, Yersinia

Symbiosis and Microbial Interactions

• Mutualism: Both organisms benefit (e.g., gut bacteria in humans).

• Commensalism: One benefits, the other is unaffected (e.g., skin flora).

• Parasitism: One benefits at the expense of the other (e.g., pathogenic bacteria).

Type of Symbiosis	Description	Example
Mutualism	Both benefit	Gut microbiota
Commensalism	One benefits, other unaffected	Skin bacteria
Parasitism	One benefits, other harmed	Pathogenic bacteria

Additional info: Microbiota refers to the community of microorganisms living in a particular environment, such as the human gut.

Viruses

Structure and Replication

Viruses are acellular infectious agents that require host cells for replication. They consist of genetic material (DNA or RNA) surrounded by a protein coat (capsid), and sometimes an envelope.

• Capsid: Protein shell enclosing viral genetic material.

• Envelope: Lipid membrane derived from host cell.

• Positive/Negative RNA Virus: Refers to the sense of the RNA genome.

• PFU (Plaque Forming Unit): Measurement of viral quantity.

Viral Life Cycle

1. Adsorption: Virus attaches to host cell.

2. Penetration: Entry of viral genome into host cell.

3. Uncoating: Release of viral genome from capsid.

4. Replication and Transcription: Synthesis of viral components.

5. Assembly: Formation of new viral particles.

6. Release: Virions exit host cell, often causing cell lysis.

Example: The lytic cycle of bacteriophage involves rapid replication and destruction of the host cell.

Additional info: Persistent infections (e.g., herpesvirus) can remain in host cells for long periods.

Eukaryotic Microorganisms

Fungi and Protozoa

Eukaryotic microorganisms include fungi, protozoa, and helminths. They have complex cellular structures and diverse life cycles.

• Fungi: Includes yeasts, molds, and mushrooms. Can cause superficial, cutaneous, subcutaneous, and systemic mycoses.

• Protozoa: Single-celled eukaryotes, some of which cause diseases such as malaria and giardiasis.

• Helminths: Parasitic worms (e.g., roundworm, tapeworm, fluke).

Life Cycles and Disease Transmission

• Definitive Host: Host in which parasite reaches maturity.

• Intermediate Host: Host in which parasite undergoes development but does not reach maturity.

• Vector: Organism that transmits pathogens (e.g., mosquito, tick).

Protozoal Disease	Life Cycle	Treatment
Malaria (Plasmodium)	Mosquito (vector) transmits sporozoites to human; liver and blood stages	Antimalarial drugs (e.g., chloroquine)
Giardiasis (Giardia)	Ingestion of cysts; trophozoite stage in intestine	Metronidazole

Additional info: Treatment depends on the life cycle stage and drug susceptibility of the organism.