Quorum Sensing in Bacteria

Quorum sensing is a sophisticated signaling mechanism employed by bacteria to regulate gene expression in response to population density. It enables bacteria to coordinate group behaviors, such as biofilm formation, virulence factor expression, and symbiotic relationships.

Key Components:

1. Autoinducers:
• Bacteria release small signaling molecules called autoinducers into their environment.
• Autoinducers accumulate as the bacterial population grows.
2. Receptor Proteins:
• Bacteria possess receptors that can detect the concentration of autoinducers.
• When the autoinducer concentration reaches a threshold (quorum), it binds to the receptors.

Function:

1. Gene Expression Regulation:
• Binding of autoinducers to receptors activates signal transduction pathways.
• This leads to changes in gene expression, influencing various cellular processes.
2. Coordination of Behaviors:
• Quorum sensing regulates behaviors that are more effective when executed by a population rather than by individual bacteria.
• Examples include the formation of biofilms, expression of virulence factors, and the establishment of symbiotic relationships.
3. Adaptation to Environment:
• Quorum sensing allows bacteria to adapt to changing environmental conditions collectively.
• It enhances survival and competitiveness in diverse ecological niches.

Examples:

• Vibrio fischeri: Bioluminescence in V. fischeri is controlled by quorum sensing, allowing the bacteria to emit light only when present in sufficient numbers.
• Pseudomonas aeruginosa: Quorum sensing regulates the production of virulence factors, contributing to the pathogenicity of this bacterium.

Applications:

• Understanding quorum sensing provides insights for controlling bacterial behaviours, offering potential strategies for disease control and biofilm management.

In conclusion, quorum sensing is a vital mechanism that allows bacteria to sense and respond to their population density, facilitating coordinated group behaviours essential for their survival and adaptation in diverse environments.

 

Gram Staining

 

Gram staining

Principle

When the bacteria is stained with primary stain Crystal Violet and fixed by the mordant, some of the bacteria are able to retain the primary stain and some are decolorized by alcohol. The cell walls of gram positive bacteria have a thick layer of protein-sugar complexes called peptidoglycan and lipid content is low. Decolorizing the cell causes this thick cell wall to dehydrate and shrink, which closes the pores in the cell wall and prevents the stain from exiting the cell. So the ethanol cannot remove the Crystal Violet-Iodine complex that is bound to the thick layer of peptidoglycan of gram positive bacteria and appears blue or purple in colour.

In case of gram negative bacteria, cell wall also takes up the CV-Iodine complex but due to the thin layer of peptidoglycan and thick outer layer which is formed of lipids, CV-Iodine complex gets washed off. When they are exposed to alcohol, decolourizer dissolves the lipids in the cell walls, which allows the crystal violet-iodine complex to leach out of the cells. Then when again stained with safranin, they take the stain and appear red in colour.

Procedure

1. Take a clean, grease free slide.
2. Prepare the smear of buttermilk or curd suspension on the clean slide with a loopful of sample.
3. Air dry and heat fix.
4. Crystal Violet was poured and kept for about 30 seconds to 1 minutes and rinse with water.
5. Flood the gram’s iodine for 1 minute and wash with water.
6. Then ,wash with 95% alcohol or acetone for about 10-20 seconds and rinse with water.
7. Add safranin  for about 1 minute and wash with water.
8. Air dry, Blot dry and Observe under Microscope.

Result

Violet coloured rod shaped gram positive  bacteria observed.