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Different RsbR paralogs in Bacillus subtilis affect cell viability when exposed to environmental stress

Osborne, Jacob
Every living organism must find a way to survive stressful situations and bacteria are no different. Bacteria deal with many kinds of stress, including energy stress like starvation or ATP depletion and environmental stress like acids, alcohols, salts, or lack of oxygen. Bacillus subtilis is a model organism that displays a unique stress response involving a large protein complex called a stressosome composed of multiple copies of several different proteins. The RsbR proteins in this stressosome are the stress sensors of the cell and elicit a response through a signal cascade once stress is sensed. There are four different types of RsbR proteins named RsbRA, RsbRB, RsbRC, and RsbRD that are present in the wild type (WT) cell. Considered individually, each of these sensors responds slightly differently to incoming stress, but it is not known whether these differences in response pattern affect cell viability. By isolating each RsbR protein into separate strains and competing them against one another under 4% Ethanol and pH 6.25 HCl stress, I have developed a hierarchy that shows which RsbR proteins outcompete the others. In 4% Ethanol, RC>RD~RB>RA>WT. At pH 6.25 (acid stress), RC>WT>RB>RD>RA. All of the stress hierarchies from competition assays show RC outcompeting the other strains, even though the WT was hypothesized to win because it exists in nature. This is most likely because of the slower, but more sustained stress response pattern of RC compared to the other strains.