The electron transport of acetate-grown Methanosarcina acetivorans
Open Access
- Author:
- Wang, Mingyu
- Graduate Program:
- Biochemistry, Microbiology, and Molecular Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 18, 2010
- Committee Members:
- James Gregory Ferry, Dissertation Advisor/Co-Advisor
James Gregory Ferry, Committee Chair/Co-Chair
Sarah Ellen Ades, Committee Member
Donald Ashley Bryant, Committee Member
Christopher Howard House, Committee Member
Ming Tien, Committee Member - Keywords:
- electron transport
acetate
Etp
Rnf
Archaea
methanogenesis
methanogen
Methanosarcina acetivorans - Abstract:
- The electron transport of marine acetate-utilizing methanogen Methanosarcina acetivorans was investigated, leading to the first identification and partial characterization of two novel ferredoxin: CoM-S-S-CoB electron transport chains. The study of an Rnf-dependent membrane-bound pathway of aceticlastic M. acetivorans that doesn’t reduce CO2 with H2 characterized members both unique to Rnf-dependent pathway and also in common with Ech-dependent ferredoxin: CoM-S-S-CoB electron transport chain in CO2 utilizing aceticlastic methanogens. These include the Rnf complex, cytochrome c, ferredoxin, Cdh, methanophenazine, heterodisulfide reductase and CoM-S-S-CoB. The purification and phylogenetic analysis of ferredoxin suggested an aceticlastic-specific ferredoxin clade among methanogens. This Rnf-dependent electron transport pathway, shared with non-CO2 utilizing Methanosarcina thermophila is analogous to Ech-dependent electron transport pathway in its location and terminal electron partners but differs from the later in that it lacks the use of hydrogenases and H2. A novel soluble ferredoxin: CoM-S-S-CoB pathway was identified in M. acetivorans by comparing soluble and membrane-bound ferredoxin: CoM-S-S-CoB oxidoreductase activities and was hypothesized to involve a HdrA: MvhD fusion protein, named Etp. Etp was heterologously overexpressed in Escherichia coli, purified, reconstituted and partially characterized for the first time, showing heavy iron-sulfur cluster content. The reduction of Etp is linked to the oxidation of ferredoxin mediated by unknown soluble factors. Finally, a model of energy conservation for M. acetivorans was constructed suggesting this soluble electron transport chain serves to bypass certain energy coupling sites and maximize energy conservation efficiency under substrate-limited scenarios.