Probing the physiological role of chlorobiumquinone in Chlorobaculum tepidum using a novel synthetic analog

Hess, Daniel
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University of Delaware
Chlorobaculum (Cba.) tepidum is a model organism for studying the anoxic autotrophic oxidation of reduced sulfur compounds. Understanding the cellular mechanisms in which these compounds are oxidized is necessary for developing bioremediation technologies that mitigate the release of toxic sulfur compounds, such as hydrogen sulfide, into the environment. Sulfide: quinone oxidoreductases (SQRs) oxidize sulfide to persulfide and donates the resulting electrons to the quinone pool. The two major quinones in Cba. tepidum are menaquinone-7 (MK-7) and chlorobiumquinone (CK). This thesis investigates the role of CK in sulfide metabolism by performing physiological studies using a novel chlorobiumquinone analog (CKA) that was chemically synthesized. Growth studies involving CKA determined that the analog inhibits growth in CK producing organisms through bacteriostatic means. Cyclic voltammetry studies showed that addition of CKA to cells has no significant impact on the ability of Cba. tepidum to uptake sulfide. However, fluorescent measurements revealed that CKA is an efficient quencher of cellular fluorescence. These results support prior work in the literature suggesting that CK is involved in sequestering energy transfer from BChl c to the reaction center complex under oxidizing conditions in order to prevent the production of highly toxic oxygen radicals. Additionally, the gene CT1509 whose gene product may be involved in the biosynthesis of CK was identified though a precomputed bi-directional BLASTP genome comparison between Cba. tepidum and Leishmania major strain Friedlin (a eukaryote that produces CK) . Future work involving the silencing of CT1509 gene expression and physiological studies of the resultant mutant will further contribute to our understanding of the biosynthesis and physiological relevance of chlorobiumquinone.