Sometimes, not seeing is believing: animated GIFs of disabled bacteria


This post goes well with the last about bacterial stress. What if the stress is only perceived because the cell is missing an important protein needed to respond to a given stress? Let’s look at an example from Azospirillum brasilense. The protein named ChsA, which breaks down the second messenger cyclic-di-GMP, was deleted from A. brasilense. ChsA enzyme activity is regulated by a protein domain called a PAS domain common to both prokaryotes and eukaryotes. This particular PAS of ChsA had a sequence predicted to sense oxygen. So what happens if the cell is missing this protein necessary to regulate cyclic-di-GMP levels by monitoring oxygen levels of the environment? Take a look:

animated bacteria gif, chemotaxis gif
A. brasilense cells deleted for the protein ChsA are unable to correctly sense oxygen and regulate cyclic-di-GMP levels within the cell. Therefore, the cell is in a constant stressed state with high c-di-GMP levels causing cells to aggregate.
animated gif, chemotaxis gif
Same as previous image but in a binary mode.

For this particular example, we were able to determine how ChsA functions within A. brasilense by measuring intracellular cyclic-di-GMP levels of cells when cells transition from aerobic to anaerobic atmosphere and from anaerobic to aerobic. In other words, when oxygen is removed or added to the gaseous atmosphere surrounding the cell suspension. Compared to wild type, ChsA deleted cells had significantly higher cyclic-di-GMP levels after oxygen was added back to the atmosphere suggesting ChsA breaks down cyclic-di-GMP when oxygen concentrations increase around the cell. So these cells have an artificially high amount of a signal for cells to produce extracellular sugar polymers leading to cell aggregation. Another example of perception being reality…

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