Monday, June 16, 2014

Glass-like Cytoplasm?!

The biology department has started a research in progress/journal club for the graduate students. Research in progress the poor sap has to present what they are doing, while journal club the student has to pick the paper and then lead the discussion. I must admit that I am skeptical about journal club because there are so few plant people that I know I will have to read a bunch of random papers that are out in left field from my beloved plants. While I do understand, and appreciate, the acquisition of knowledge outside of my corner, I have sooooo much in my corner it's just one more thing.

Then, the first week of journal club this paper showed up:  The bacterial cytoplasm has glass-like properties and is fluidized by metabolic activity,  Parry et al. 2014. you've seen the movie Sweet Home Alabama, you'll remember the iconic scene at the end where he is putting out lightening rods on the beach to make "beach glass." It was kind of an important scene ;)  In this movie's physics, lightening hits the sand and liquifies it, which then recools into beautiful sculptures. Apparently, bacteria can do a similar process but in reverse and using metabolism instead of lightening!

Cytoplasm is the fluid that fills the cell. In bacteria, everything exists in the cytoplasm, DNA, ribosomes, enzymes, carbohydrates, etc., making it very crowded. Parry and his colleagues made "a serendipitous observation while studying the bacterial intermediate filament protein crescentin," where crescentin movement within the cells stopped when metabolism stopped. Since we've always visualized particles moving around based on diffusion (higher to lower concentrations, like how perfume spreads from the bottle to your nose), seeing a molecule stop moving because the cell metabolism ceased is just plain weird!

Through several incredible methods, including developing a genetically engineered probe, florescent tagging, and good old fashion microscopy, they were able to determine that larger particles have similar physics to that of liquids as they transition to glass, such as nonergodicity, caging and dynamic heterogeneity.  Nonergodicity simply means that their probes were confined to certain areas instead of diffusing freely as would be predicted in non-glass-like liquids. They showed larger molecules can become trapped within small areas due to crowding (caging) in metabolically inactive cells, but when metabolism activates these cages are rearranged the the molecules released. The cells also showed dynamic heterogeneity, meaning that "slow" vs "fast" particles can exist and exhibit very different movement patterns.

Thus, having glass-like liquid properties probably acts as a way for bacteria to exert fine scale control over activities essential to survival, as certain molecules will only be released from the cages when metabolically required. This could also indicate that in bacterial cells that are dormant (not metabolically active) cytoplasm fluidity is greatly reduced by glass-like regions, and preserving the cellular setup so that when conditions allow the bacteria can resume growth in an efficient fashion.

Understanding this on/off switch from fluid to glass-like and back has the potential to enhance our understanding of metabolism. Now I can't wait to see if these same principles hold true in eukaryotic cells, or even within individual organelles!

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