title: Deletion of alternative pathways for reductant recycling in Thermococcus kodakarensis increases hydrogen production.
abstract: Hydrogen (H₂) production by Thermococcus kodakarensis compares very favourably with the levels reported for the most productive algal, fungal and bacterial systems. T. kodakarensis can also consume H₂ and is predicted to use several alternative pathways to recycle reduced cofactors, some of which may compete with H₂ production for reductant disposal. To explore the reductant flux and possible competition for H₂ production in vivo, T. kodakarensis TS517 was mutated to precisely delete each of the alternative pathways of reductant disposal, H₂ production and consumption. The results obtained establish that H₂ is generated predominantly by the membrane-bound hydrogenase complex (Mbh), confirm the essential role of the SurR (TK1086p) regulator in vivo, delineate the roles of sulfur (S°) regulon proteins and demonstrate that preventing H₂ consumption results in a substantial net increase in H₂ production. Constitutive expression of TK1086 (surR) from a replicative plasmid restored the ability of T. kodakarensis TS1101 (ΔTK1086) to grow in the absence of S° and stimulated H₂ production, revealing a second mechanism to increase H₂ production. Transformation of T. kodakarensis TS1101 with plasmids that express SurR variants constructed to direct the constitutive synthesis of the Mbh complex and prevent expression of the S° regulon was only possible in the absence of S° and, under these conditions, the transformants exhibited wild-type growth and H₂ production. With S° present, they grew slower but synthesized more H₂ per unit biomass than T. kodakarensis TS517.
authors.affiliation: Department of Microbiology and Center for RNA Biology, Ohio State University, Columbus, OH 43210, USA. santangelo.11@osu.edu
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Santangelo
authors.forename: L'ubomíra
authors.initials: L
authors.lastname: Cuboňová
authors.forename: John N
authors.initials: JN
authors.lastname: Reeve
mesh_terms: D015870:Gene Expression; D006859:Hydrogen / Q000378:metabolism*; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D010957:Plasmids; D019163:Reducing Agents / Q000378:metabolism*; D017384:Sequence Deletion; D019712:Thermococcus / Q000235:genetics* / Q000378:metabolism*
chemical_list: D019163:Reducing Agents; D006859:Hydrogen