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Discussing Quorum Sensing

Define the term "quorum sensing" and describe (at the cellular/biochemical level) the mechanism by which microbes participate in this phenomenon.
Provide a real-world example of quorum sensing by a) naming a microorganism that carries out quorum sensing, b) describing the microbial activity that is induced, and c) briefly describing the advantage this activity provides to the microbe .
Given what you know about the role of quorum sensing in the context of certain infections microorganisms and the human diseases they cause, describe a means of treatment or therapy that would take advantage of a pathogen's reliance on quorum sensing.

Solution Preview

Hello! Thanks for using Brainmass! I'm going to respond to this by giving you a general explanation of both biofilms and quorum sensing, since the two go hand-in-hand. I'm going to go in depth into the formation of biofilms and what happens when the quorum sensing genes kick on. Once you go over this, you can use that information to figure out a means of treatment or therapy. I'll give you some hints on that last part, though. Don't worry! :) Here we go.

First up, my plan of attack. There's a lot of information out there about biofilms (they're the darling of the microbiology world at the moment, and lots of time and effort is going into studying them), so there's no way I'll be able to memorize everything about them in the next few weeks. What I can do, however, is focus on a model specimen, and know everything about that particular model.

Pseudomonas aeruginosa is a bacterium that is frequently found in biofilms, and happens to be one of the most studied species in the biofilm world. (This is probably due to its annoying tendency to infect humans).
This makes it the perfect subject for me to use as my model specimen. Let's get to it!

First and foremost: what are biofilms?

Biofilms are communities of microorganisms embedded and immobilized in an extracellular polymeric substance (EPS) attached to a solid surface. The biofilm gives microorganisms protection from things like desiccation, predation, and antibiotics, and allows them to share water and nutrients. It has also been proposed that biofilms allow for the sharing of DNA, thereby facilitating the transfer of beneficial genes from cell to cell. This community organization is in direct opposition to the way we have studied microorganisms for many years: as free living single-celled organisms (called planktonic organisms).

Biofilms are highly variable, and their exact make up and structure changes with species, temperature, stress, nutrients, and other environmental factors. While this is super annoying for those of us who want to know everything about biofilms, it's actually a very good strategy for the micro communities that utilize these biofilms as environments: great diversity keeps a single organsim from decimating the world-wide biofilm population.

What makes a biofilm a biofilm is the presence of the extracellular polymeric substance (EPS for short).

"Extracellular" is outside the cell; "polymeric" is a repeated molecular unit
This stuff was originally called "extracellular polysaccharides" until scientists figured out that there were lipids, proteins and DNA involved as well. Luckily, they were able to come up with a phrase that kept the EPS acronym, so everything worked out in the end.

In order to form biofilms, planktonic bacteria go through five primary stages of biofilm development:

1. Initial attachment

2. Irreversible attachment

3. Maturation I

4. Maturation II

5. Dispersal

The five stages.
I'll look at these in order, using P. aeruginosa as a model organism.

1. Initial attachment.

First and foremost, the planktonic bacteria need to get to the surface of something in order to form a biofilm (remember that the definition of a biofilm is a community of bacteria embedded in an external matrix attached to a solid surface). Pseudomonas aeruginosa does this via diffusive transport

Remember this type of diffusion drawing from your bio classes? Yep, bacteria move the same way.
convective transport

convective transport is when the bacteria gets carried along with the movement of a fluid...kinda like a surfer on a wave
and active transport driven by bacterium flagella.

This species has a single, polar flagellum that it uses to move.
Once the bacterial cells arrive at an appropriate spot, they attach to the surface. They are able to attach due to their flagellum, type IV pili, extracellular DNA, and Psl polysaccharides.

The flagellum is involved in attachment due to its stators.

You see, the flagellum works by spinning. There's a spinning rotor portion, and a stationary stator portion, within which the rotor spins. In P. aeruginosa there are two stators, and both must be present for biofilm ...

Solution Summary

A general explanation of both biofilms and quorum sensing is presented here. References are also provided to justify the assertions.

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