Friday, May 15, 2009

Throwing the Clutch (not the Brake) on a Bacterial Flagella

ResearchBlogging.orgFor most my of readers, it is common knowledge that bacteria are more than just singled celled entities; and instead bacteria are complex organisms capable of undergoing large-scale, multicellular activities. Of particular interest to many current microbiologists, is the development of biofilms.

These multicellular structures are likely how many bacteria exist in the environment, and are implemented in a variety of diseases. Taken alone, biofilms are fascinating, but I have a keen interest in understanding exactly how a bacterial cell decides it is time to create a biofilm. (In reality, I have a keen interest in how a bacterial cell decides it is time to do anything, but that is beside the point)

While studying the switch between motility and biofilm development in Bacillus subtilis, Daniel Kearns of Indiana University, wanted to know the status of the flagella during the switch.

Mutants of the biofilm regulator sinR are constitutively in a biofilm state and are nonmotile. However, flagellar genes are still expressed and flagella are still produced. The question then became what is preventing the flagella from moving while in a biofilm.

The first idea would be that the extracellular matrix is physically inhibiting the movement of the flagella. By knocking out a gene required for matrix production (epsH), Kearns saw that the flagella became free, but were unpowered.

Then, as any good geneticist, he screened for mutants that were able to suppress the non-motility phenotype of a sinR, epsH double mutant. All of these mutants mapped to a putative glycosyltransferase (epsE) within the matrix operon. Furthermore, expression of epsE alone was sufficient to inhibit flagellar motion, and known conserved glycosyltransferase residues were not required for inhibition.

This brings up the questions: Where is epsE acting? and Is it a brake (completely stopping all flagellar movement) or a clutch (preventing active rotation)?
By selecting for supressors of redundant epsE, the group found that all suppressors mapped to the fliG gene; a gene known to encode the transduction motor between the proton pump (motAB) and flagellar basal body. So, somehow epsE acts to inhibit the motor.

Furthermore, upon examining flagellar motion (in some awesome movies available here) Kearns showed that the flagella were not braked, that is, the flagella were still capable to rotate freely (and in fact did), however all rotation was due to Brownian motion. This implies that the flagella were disconnected from the motor, rather than stopped completely.

So, epsE is acting as a clutch to disconnect the flagellar basal body from the motor. This actually makes quite a bit of sense. If the cell no longer requires flagellar motion as it went into biofilms, it could do a variety of techniques. One is that it could shut off gene expression for the flagella. However, it would take many generations before its progeny were non-motile and the flagellar apparatus was diluted out. Another is that it could put a brake into the flagella and prevent motion entirely. But, this would cause lots of cell envelope stress while in a biofilm. Brownian motion alone could potentially tear the cell apart.

This leaves the cell with the clutch option. Capable of stopping flagellar motion quickly while keeping the cell envelope intact. Due to its high homology to glycosyltransferases, epsE likely represents an example of a duplicative evolution; whereby a duplication of an enzyme leads to the capability to take one copy of said enzyme and "play with it" to create new functions. In this case a sugar-acting enzyme has become a structural protein in the flagellar apparatus.

Blair, K., Turner, L., Winkelman, J., Berg, H., & Kearns, D. (2008). A Molecular Clutch Disables Flagella in the Bacillus subtilis Biofilm Science, 320 (5883), 1636-1638 DOI: 10.1126/science.1157877

Other Articles of Interst:
Extracellular Membrane Vesicles in Bacteria: Taking Quorum Sensing in New Directions
Altruism in Bacteria: Allowing Yourself to Die for the Good of the Species
Where the Wild Microbes Are: A New Theory in How Pathogens Survive Food Processing

Saturday, May 9, 2009

Phage + Metal = Battery? By now, many people have read about Angela Belcher, a professor at MIT, and her lab's recent developments in the use of bacteriophages as a component of batteries. Having had a very distinct privilege to hear her speak yesterday, I wish to share what I have learned.

In a broad sense, the goal of her lab is to give inorganic compounds (batteries, medical devices, solar cells, etc), "genetic intelligence." That is, to give the power of evolutionary adaptation and self-correction to inanimate objects. Life evolved the ability to perfectly use the ions and metals present in its environment, things like calcium, silica, etc. However, she wants to know what happens when we allow life to evolve in the presence of technologically important compounds, like gold, silver, aluminum, platinum, etc.

One of the original goals was to develop a biological system that could recognize and mark atomic scale cracks in layered materials. She set to do this using a phage library. The phage, M13, is capable of having many of its parts replaced with random gene sequences, allowing us to add in peptides that allow recognition for any particle of our choosing. (A concept referred to as "phage display" and has been used for lots of detection assays)

She selected for attachment proteins that allowed the phage to attach to atomic scale cracks in the alloy used in engine blocks and computer parts. You can then propagate, mutate, and select for phages that have tail fibers with the strongest possible affinity for the substrate of your choosing. This was very successful, and from my impression, is being scaled up to allow identification of these atomic cracks in engine blocks, airplane wings, and helicopter blades. (She is now figuring out how to mesh the identification of the cracks via phage, to self-healing properties via metal nucleation)

She then found that the proteins in the phage body could be altered as well. Using similar techniques she found that metal ions could be nucleated in both poly crystalline and mono crystalline structures to the phage body. Thus allowing the creation of nanotubes (with a phage inside). By altering ratios of metal ions added, she can create very specifically composed alloys. Importantly, all of this is done at STP, with a rare exception (Ag-Pt tubes for fuel cells) requiring 80C temperatures. She can also rid the system of organic material by heating to >100C, but keep the inorganic structures intact.

Using phages with affinities for cobalt oxide, lithium, these scientists managed to create a functional battery that is only on the order of nanometers in thickness. Paper thin batteries that have the capacity and power to replace automotive batteries now. The batteries are capable of being charged and recharged numerous times without losing power or capacity. (This was a problem at first). They are very fast to produce (<6hrs)>
If you can think of any application for nanowire like phage nucleation of metals, her team is already working on it. This battery concept is definitely going to be an important milestone in development of new energy storage, usage, and production.

Normally when we think of applications of microbial genetic systems, we think of human health and perhaps fermentations. Now, we can truly see the power when genetics are applied to technologically challenging engineering applications.

Lee, Y., Yi, H., Kim, W., Kang, K., Yun, D., Strano, M., Ceder, G., & Belcher, A. (2009). Fabricating Genetically Engineered High-Power Lithium Ion Batteries Using Multiple Virus Genes Science DOI: 10.1126/science.1171541

Other Articles of Interest:
Utilizing Natural Killers: Phage-Based Antimicrobials

Evolution of Phage Capsid and Genome Size
How Far Do Those Phages Stretch?
Phages with Horns? What's Next?
I Got You Phage

Blogging for Bacteriophages is Back

After a rather long sabbatical, Blogging for Bacteriophages is ready to start reporting the exciting and interesting news in the world of microbiology.

The layout is finally optimized. Comments are fully functional. Blogger has also introduced "reaction boxes" to allow you to give feedback with just one click.

Most importantly, I finally have time to devote to publishing again. A realistic goal is 2 articles each month, with a hopeful goal of 4 per month. As always, I would love input from others in the field, especially other graduate students.

I am looking forward to sharing some fun and ground breaking science, as well as interesting experiences I have had over the past few months. I have been privilaged to listen to some fantastic science coming from notable speakers, such as James Watson, Matthew Meselson, Angela Belcher, Pete Greenberg, and many others.

Here's to a new start!