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CtrA Positively Regulates Flagella Expression in Rhodospirillum centenum Mark Pelka Faculty Advisor: Terry Bird Department of Biology
Rhodospirillum centenum is a metabolically diverse bacterium that grows through anaerobic and aerobic respiration or anoxygenic photosynthesis. R. centenum can differentiate between swim and swarm cells and, to avoid starvation when nutrients are scarce, can also develop into dormant cysts. Because they have no active metabolism, cyst cells do not require nutrients and are resistant to desiccation. We hypothesized that a pathway, which included three gene products, was responsible for initiating encystment. The proteins involved in this pathway include Cyd2, a histidine kinase, ChpT, a phosphorelay protein, and CtrA, a response regulator. Through observation of different knockout phenotypes we discovered that it is unlikely that all three proteins function in the same pathway in R. centenum. However, ChpT and CtrA do appear to be in the same pathway that regulates flagella expression because analysis of strains with chpT or ctrA mutations exhibited lower expression of genes that contribute to flagella biosynthesis.
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Characterization of a Novel CLC Homolog from Citrobacter koseri Sabrina Phillips Faculty Advisor: Kimberly Matulef Department of Chemistry and Biochemistry
CLC chloride-transport proteins are expressed ubiquitously and are vital to several physiological processes. This family is distinctive in that some members are chloride channels while others are chloride/proton antiporters. To better understand the mechanics of CLC proteins, we have characterized a novel bacterial homolog, CLC-b. CLC-b is 24% identical and 42% similar in sequence to CLC-ec1, but lacks several highly conserved amino acids near the chloride binding sites. Despite lacking these regions, we found that CLC-b does transport chloride ions. CLC-b contains an isoleucine at the position equivalent to the intracellular proton transfer glutamate. Since all known CLC ion channels contain a hydrophobic residue at this position whereas all antiporters contain a protonatable residue, we had hypothesized that CLC-b would be an ion channel. To our surprise, we found that CLC-b is a chloride/proton antiporter. Hence, a protonatable residue at the intracellular glutamate position is not necessary for proton transfer.
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Sources of Brown Carbon: Aldehyde/Amine Reactions in the Aerosol Phase Michelle Powelson Faculty Advisor: David De Haan Department of Chemistry and Biochemistry
The formation of light-absorbing ‘brown carbon’ in atmospheric aerosol has an important impact on climate. However, the processes and precursors responsible for brown carbon formation have not been identified. Several carbonyl compounds are present in clouds and have the potential to create brown products when reacted with ammonium sulfate or primary amines such as methylamine. The formation of light-absorbing products from these reactions is characterized as a function of temperature and cloud-relevant pH (from 3-6) using UV Visible spectroscopy. The formation of light-absorbing products in the methylamine-methylglyoxal reaction was faster at higher pH and higher temperature, consistent with NMR kinetics measurements. It was found that glycolaldehyde produces light-absorbing products at the fastest rate of any aldehyde tested, un i v ers i t y o f san d i egO
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