Bacterial Genetics and Gene Transfer Methods

Bacterial Genetic Transfer

• Bacterial genetic transfer involves the movement of genetic material between bacteria.
• This transfer can occur through various mechanisms including transformation, transduction, and conjugation.
• Genetic transfer provides new genetic information to microorganisms.
• This helps them adapt to changing environments.
• From a clinical perspective, it aids in the transfer of antibiotic resistance genes from resistant bacteria to sensitive ones.

Intended Learning Outcomes 1

• Students should understand plasmids, bacteriophages, transposons, and pathogenicity islands.
• Students should understand the purpose of quorum sensing.
• Students should understand the role of plasmids, phages, and transposons in gene transfer processes such as conjugation, transformation, and transduction.

Intended Learning Outcomes 2

• Students should know the role of recombination in bacterial genetic transfer.

Introduction

• Acquiring genes through genetic transfer provides new genetic information to microorganisms.
• This new genetic information can benefit the bacteria by helping them survive changing environments.

Importance of Genetic Transfer

• From a clinical perspective, genetic transfer aids in the transfer of antibiotic resistance genes from resistant bacteria to sensitive bacteria.
• Plasmids and bacteriophages can transfer other factors such as virulence genes (e.g., toxins) to bacteria that previously lacked them.

The Bacterial Gene and Expression

• Bacteria usually have only one chromosome.
• Bacteria may also possess extrachromosomal genetic elements such as plasmids and bacteriophages.
• Plasmids and bacteriophages are independent of the bacterial chromosome.
• These elements can be transferred from one cell to another.

Plasmids 1

• Images show bacterial DNA and plasmids within a bacterial cell.

Plasmids 2

• Plasmids are small genetic elements.
• They can replicate independently of the bacterial chromosome.
• Plasmids can facilitate genetic change.
• Plasmids carry genetic information.

Plasmids 3

• The F plasmid is crucial for bacterial conjugation and transfer of resistance to certain antibiotics (R plasmids).
• R plasmids carry genes that confer resistance to specific antibiotics.
• R plasmids can be transferred to other bacteria through conjugation.
• Without antibiotic resistance genes, a bacterium is considered sensitive to that antibiotic.

Plasmids Cont'd

• Diagrams illustrate plasmid integration, replication, and transfer.

Bacteriophages 1

• Bacteriophages are bacterial viruses.
• Bacteriophages can contain either DNA or RNA genomes.
• Bacteriophages are protected by protein shells.
• Bacteriophages can exist outside of a host cell and be transferred between cells.
• Bacteriophages can infect bacterial cells.

Bacteriophages 2

• Illustrations depict the phage's lytic cycle, injection of phage DNA into a bacterial cell, and the formation of new phage particles.
• Bacteriophages can transfer genes from one bacterium to another.

Bacteria Chromosome

• The bacterial genome consists of genes located in both the bacterial chromosome and extrachromosomal genetic elements.

Pathogenicity Islands

• Genes are organized into islands, such as pathogenicity islands.
• Pathogenicity islands share functions or coordinate control of functions.
• Pathogenicity islands exist in Gram-negative and Gram-positive bacteria.

Pathogenicity Islands 2

• Genes for virulence mechanisms may be grouped into pathogenicity islands.

Quorum Sensing

• Quorum sensing is a process where bacteria produce specific small molecules when sufficient numbers of bacteria are present.
• Quorum sensing activates virulence and other genes.

Quorum Sensing Examples

• The activation of toxin production and increased virulence in Staphylococcus aureus is linked to increased cyclic peptide concentrations.
• Biofilm production in Pseudomonas spp. is triggered by a critical concentration of N-acyl homoserine lactone (AHL).

Transposons

• Transposons are transferable genetic elements.
• Transposons are mobile genetic elements.
• Transposons can jump from one position to another within the genome or between different genetic structures.
• Transposons exist as replicative or non-replicative.

Transposons 2

• Transposons are DNA segments.
• Transposons can move locations.
• Transposons can move between chromosomes, plasmids, and even different bacteria.

Two methods of transposition

• Illustrations show the "cut-and-paste" and "copy-and-paste" mechanisms of transposition.

Genetic Transfer

• The mechanism for DNA transfer from a donor to a recipient cell.
• In bacteria, there are three main methods for genetic transfer: transformation, transduction, and conjugation.
• Bacterial recombination must occur after transfer.

Microbial genetic transfer between cells

• Three mechanisms of gene exchange in cells include conjugation, transformation, and transduction.
• Diagrams illustrate the three processes.

Conjugation

• Conjugation involves the transfer of genetic material between bacteria through direct contact.
• The process is typically one-way, from the donor cell to the recipient cell.
• The process involves using a pilus.

Conjugation Cont'd

• Plasmids often carry genes that enable the formation of a bridge, or pilus, between two bacteria
• Plasmids are often replicated and transferred from F+ (donor) cells to F- (recipient) cells.

Summary Question 1

• Conjugation is a method of genetic transfer that involves direct contact between bacteria.

Transformation

• Release of DNA from dying or lysed bacteria.
• Other bacteria of the same species absorb these fragments.
• Those fragments are incorporated into bacterial DNA through recombination.
• Process of transformation results in a recombinant cell.

Transformation 1 & 2

• Images illustrate the process of recipient cells incorporating donor DNA fragments.

Transduction

• Transfer of DNA between bacteria by a bacteriophage.
• Bacteriophages carry donor DNA fragments into recipient cells.

Transduction Cont'd

• Illustrations depict the phage's attachment and injection into a bacterial cell; DNA fragment transfer; cell lysis.

Genetic Recombination

• Exchange between two DNA molecules.
• Forms new gene combinations on the chromosome.
• Involves the crossing over of two homologous chromosomes.
• Leads to genetic diversity in a population.

High Frequency Recombination (Hfr)

• Transfer of a part of the donor's chromosome to the recipient bacterium.
• Occurs via recombination between Hfr chromosome fragment and the recipient F chromosome.

Genetic Mechanisms of Evolution

• Diagram illustrates the various methods used in bacterial evolution, including transformation, conjugation, and transduction, along with examples of how genetic material can move from one bacterial cell to another.

Summary

• Overview of transformation, transduction, conjugation, and transposition.
• Diagrams summarizing the different procedures and processes for gene transfer.

References

• Text gives reference to specific chapters of a book, Medical Microbiology by Murray, Rosenthal, and Pfaller.

This quiz explores various methods of gene transfer in bacteria, including conjugation, transformation, and transduction. You will learn about key concepts such as plasmids, R plasmids, transposons, and quorum sensing. Test your knowledge on genetic recombination and the role of bacteriophages in bacterial genomes.