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Investigation of Sulfur Salvage Pathways in Rhodopseudomonas palustris

Miller, Anthony Raymond, Miller
http://rave.ohiolink.edu/etdc/view?acc_num=osu1511908420156965

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Molecular, Cellular and Developmental Biology.
Ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) is the key enzyme for carbon fixation in the Calvin-Benson-Bassham (CBB) reductive pentose phosphate pathway. In addition, many bacteria possess a RubisCO-Like Protein (RLP). These form IV RubisCOs have high sequence and structural similarity to bona fide RubisCO, but are unable to assimilate CO2. Of the six various subgroups of RLPs, only two groups contain a RLP whose function has been elucidated within their respective organism. All characterized RLPs to date have been shown to be involved with some aspect of sulfur metabolism. Recently, it was discovered in Rhodospirillum rubrum, that its form IV- DeepYkr RLP functions in a novel methionine salvage pathway (MSP) wherein the dead- end metabolic by-product, 5’-methylthioadenosine (MTA), is metabolized into methanethiol and subsequently methionine. This novel pathway was found to link MTA metabolism with isoprenoid biosynthesis and thus was named the MTA-isoprenoid shunt. The closely related bacterium Rhodopseudomonas palustris is the only known sequenced organism to date that contains two RubisCO genes (cbbLS and cbbM) and two RLP genes (rlp1 and rlp2). The R. palustris RLPs belong to separate phylogenetic subgroups (RLP1, IV-DeepYkr; RLP2, IV-Photo) and neither RLP has been fully characterized in vivo. Thus this organism provides a useful model to study RLP function. Like R. rubrum, R. palustris is able to grow using MTA as a sole sulfur source, however, the manner in which R. palustris metabolizes MTA under aerobic conditions is unknown. In the current study we used directed metabolite analysis, gene knockouts and in vitro assays to elucidate the R. palustris MSP and the possible role the RLP enzymes play in MTA metabolism. Our observations indicated that R. palustris contains a functional MTA-isoprenoid shunt in which only the RLP1, not RLP2, is required. Moreover, R. palustris mutant strains lacking a functional MTA-isoprenoid shunt were still capable of MTA-dependent growth and corresponding methanethiol production, suggesting an additional pathway is present for aerobic MTA metabolism. Further studies revealed that R. palustris contained a second, previosly unknown aerobic MTA metabolic pathway, characterized by a Class II Aldolase-Like Protein (Ald2) that seemingly leads to a methanethiol intermediate. This same enzyme is also known to function in a strictly anaerobic MTA metabolic pathway in R. palustris in which ethylene in lieu of methanethiol is formed. R. palustris mutant strains lacking a functional MTA-isoprenoid shunt and Ald2 pathway still supported anaerobic MTA-dependent growth, indicating that a novel route for anaerobic MTA metabolism likely exists. Moreover, unlike R. rubrum, growth phenotypes of RubisCO deletion strains suggest that RubisCOs are not required for anaerobic MTA metabolism in R. palustris. However, continued investigations uncovered a possible linked between a transsulfuration pathway via cystathionine beta synthase and anaerobic MTA metabolism. Several observations provided here necessitate thoughtful and investigative extensions of this work. It will be of interest to further study sulfur metabolism in R. palustris to gain insight into the regulation of MTA metabolism and the environmental impacts of resulting methanethiol production. Additionally, exploring RLP2 function in R. palustris will provide impactful information towards understanding and advancing the RLP field.
Robert Tabita, PhD (Advisor)
226 p.
Microbiology
Sulfur Salvage Pathways; Rhodopseudomonas palustris

Recommended Citations

Citations

  • Miller, Miller, A. R. (2017). Investigation of Sulfur Salvage Pathways in Rhodopseudomonas palustris [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1511908420156965

    APA Style (7th edition)

  • Miller, Miller, Anthony. Investigation of Sulfur Salvage Pathways in Rhodopseudomonas palustris. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1511908420156965.

    MLA Style (8th edition)

  • Miller, Miller, Anthony. "Investigation of Sulfur Salvage Pathways in Rhodopseudomonas palustris." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1511908420156965

    Chicago Manual of Style (17th edition)

osu1511908420156965
107
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