Bacterial Adaptation and Survival Quiz

Bacterial Adaptation and Survival

• Bacteria adapt rapidly to changing circumstances and pressures.
• Most DNA changes are lethal.
• Advantageous mutations, in the right conditions, lead to rapid proliferation of the organism.
• Single nucleotide polymorphisms (SNPs) are one type of genetic change in bacterial DNA.

Lecture Aims

• Explore genetic mechanisms by which bacteria acquire new genes that influence their survival.
• Explain how genetic changes enhance a bacteria's ability to cause disease.
• Discuss how bacteria use different mechanisms to sense and communicate within their environment.

Genetic Change Drivers

• Bacteria's genetic change is driven by "tiny boxes of secrets" (a reference to genetic mechanisms).

Bacterial Multiplication Rates

• Humans have longer generation times (10-12 years for puberty, 9 months gestation).
• Bacteria have much shorter generation times (20-25 minutes for a doubling time).
• Bacteria can rapidly reproduce.
• A single bacterial clone can quickly generate a vast colony in 8 hours (108 colonies).
• The rapid multiplication of bacteria has significant evolutionary implications.

Bacterial Mutations

• Adaptations of bacteria may result from mutations that alter antibiotic efficacy.
• Adaptations may also alter receptor recognition of host tissue and the response of the host's immune system.
• Bacteria can gain genes associated with virulence factors like toxins and adhesins.

Acquiring New Genetic Traits

• Horizontal gene transfer is the acquisition of new genetic traits in bacteria.
• This process enables rapid growth and spread within bacterial populations.

Horizontal Gene Transfer Mechanisms

• Natural Transformation: Uptake and incorporation of "naked" DNA.
• Conjugation: Genetic exchange between bacteria.
• Transduction: Genetic exchange during or as a consequence of phage predation (infection).

Transformation

• Transformation occurs when bacteria take up and incorporate "naked" DNA.
• Transformation is a mechanism for natural repair that can involve the uptake of foreign DNA.
• Some bacteria naturally become competent (capable of accepting DNA) in response to specific compounds released by other organisms.
• Sometimes transformation can result in antibiotic resistance.

Conjugation (Bacterial Sex)

• Conjugative plasmids carry genes for pilus (protein tube) formation and transfer of genetic material.
• Transfer of DNA is initiated by a special pilus extending from a donor cell.
• Transfer occurs in close proximity of cells (by contact).

Transduction (Phage Predation)

• Bacteriophages infect bacteria and often have two reproduction lifecycles:
• Lytic cycle: Genome replication and destruction of the bacteria.
• Lysogenic cycle: Integration of the phage genome into the bacteria's chromosome.

Integration of New DNA - Pathogenicity Islands

• Insertion of foreign DNA into bacterial chromosomes is often detected by differences in GC content.
• Large DNA inserts (pathogenicity islands) often encode virulence traits.

Chromosomal Integration/Excision

• Introduced DNA sometimes doesn't persist due to restriction systems that recognize foreign DNA sequences.
• Endonuclease activity can degrade the introduced DNA.
• Persisting DNA can integrate and multiply within a bacteria's chromosome.

Capacity to Sense and Respond

• Bacteria use multiple mechanisms to regulate gene expression due to their resource constraints.
• Quorum sensing is a method for communication between bacteria based on density.
• Environmental sensing, using two-component systems, allows individuals to respond to changes in their external environment.

Symbiotic Relationship (Aliivibrio fischeri)

• Aliivibrio fischeri produces fluorescent light that helps to camouflage squid.

Quorum Sensing (Bacterial Tweeting)

• Quorum sensing is defined as a minimum number of bacteria needed for coordinated response.
• The behavior of bacteria changes based on their population density, which triggers the accumulation of autoinducer proteins.

Quorum Sensing in Aliivibrio fischeri

• Lux operon controls light production in A. fischeri.
• LuxR produces a transcription activator.
• Luxl produces AHL.
• High AHL binds to LuxR, increasing activation of luxl and resulting in expression of lux genes and light production.

Quorum Sensing in General

• Many bacteria exploit quorum sensing to control expression of traits.

Environmental Sensing and Two Component Signal Transduction

• Transmembrane sensor kinase is a sensor that detects external environmental conditions.
• Phosphorylation cascade with a response regulator leads to gene expression changes.

Goldilocks Syndrome

• EnvZ/OmpR two component system (in pathogens like Salmonella) ensures optimal nutrient intake.
• Lifestyle exposure to different nutrients is reflected in the membrane pore size.
• OmpF pores are larger and susceptible to osmotic shock, while OmpC pores are smaller and less susceptible to osmotic shock.

Pore Size and Bacterial Sensing

• OmpC and OmpF pore variations in response to osmotic stress.

Other Two Component Regulation Examples

• PhoPQ sensing low Mg+ ions found within phagolysosomes during infection.
• PhoPQ system influences virulence traits and intracellular survival in bacteria.

Transcriptomics

• Understanding bacterial adaptation to various environments using mRNA sequencing.
• Increased gene transcripts and adaptation are correlated in a given bacterial niche.

Comparative Transcriptomics

• Using mRNA sequencing to identify genes that are up-or down-regulated in bacteria experiencing particular environmental conditions.

Lecture Summary

• The lecture highlighted bacterial adaptation to different environments, which include their ability to mutate and acquire new genetic characteristics.
• The lecture explained how bacteria communicate and sense their environment through different mechanisms, including quorum sensing and two-component systems.