Bacterial Genetics: Mechanisms and Applications

1. Concept:

• Pure culture: Bacteria originating from a single bacterial cell, possessing identical genetic material and exhibiting similar characteristics.

• Genetics: Preservation of stable bacterial traits across generations.

2. Mutations:

• Types of mutations:

• Spontaneous mutations: Occur naturally.

• Induced mutations: Triggered by external factors like chemicals or radiation.

• Location of mutations: DNA.

• Consequences of mutations:

• Abrupt alteration of a trait within a population, leading to new bacterial strains called variants.

• Characteristics of mutations:

• Random

• Stable

• Independent

• Rare (approximately 1 mutant bacterium per 10^8 bacteria)

• Specific (related to a particular trait)

• Results of mutations:

• Morphological changes: May lead to omission in testing.

• Trait variations: Impact bacterial identification.

3. Transfer of Genetic Material:

• Mechanisms:

• Transformation

• Conjugation

• Transduction

4. Transformation:

• Mechanism: Transfer of a DNA segment from a donor bacterium to a recipient bacterium.

• Experiments:

• Griffith: Proposed that the capsule caused transformation -> INCORRECT

• Avery: DNA caused transformation -> CORRECT

• Conditions:

• Donor bacterium must be broken down to release DNA.

• Recipient bacterium must be in a specific physiological state to allow DNA entry.

• Donor and recipient bacteria must be of the same species or closely related, as the genes require homology.

• Application: Vaccine production.

5. Conjugation:

• Mechanism: Transfer of genetic material from a male bacterium to a female bacterium through a conjugation bridge.

• Experiments:

• Lederberg and Tatum: Discovered conjugation.

• Hays: Identified sex (male donor, female recipient).

• Sex Factor (F Factor):

• F+: Located in the bacterial cytoplasm.

• Hfr: Integrated into the chromosome.

• F’: F carrying a chromosomal segment, located in the cytoplasm.

• Stages:

• Male bacterium contacts female bacterium, forming a conjugation bridge.

• Transfer of genetic material from the male to the female bacterium.

• Integration of the transferred DNA segment.

6. Transduction:

• Mechanism: Transfer of genetic material through temperate phages.

• Experiment: Zinder and Lederberg.

• Types of transduction:

• Generalized and non-specific transduction: Transfers any DNA segment.

• Complete: Integration of genes.

• Incomplete: No gene integration.

• Specialized and specific transduction: Transfers a specific DNA segment.

7. Plasmids:

• Circular DNA molecules outside the chromosome, capable of self-replication.

8. Transposons:

• DNA segments capable of integrating into chromosomes or plasmids at different locations.

• Carry genes conferring antibiotic resistance and bacterial virulence.

Conclusion: Understanding bacterial genetics enables us to apply it in various fields, including vaccine production, disease treatment, and molecular biology research.