A Novel CO-Responsive Transcriptional Regulator and Enhanced H 2 Production by an Engineered Thermococcus onnurineus NA1 Strain

Genome analysis revealed the existence of a putative transcriptional regulatory system governing CO metabolism inThermococcus onnurineus NA1, a carboxydotrophic hydrogenogenic archaeon. The regulatory system is composed of CorQ with a 4-vinyl reductase domain and CorR with a DNA-binding domain of the LysR-type transcriptional regulator family in close proximity to the CO dehydrogenase (CODH) gene cluster. Homologous genes of the CorQR pair were also found in the genomes ofThermococcus species and “Candidatus Korarchaeum cryptofilum” OPF8. In-frame deletion of eithercorQ orcorR caused a severe impairment in CO-dependent growth and H2 production. WhencorQ andcorR deletion mutants were complemented by introducing thecorQR genes under the control of a strong promoter, the mRNA and protein levels of the CODH gene were significantly increased in a ΔCorR strain complemented with integratedcorQR (ΔCorR/corQR ↑ ) compared with those in the wild-type strain. In addition, the ΔCorR/corQR ↑ strain exhibited a much higher H2 production rate (5.8-fold) than the wild-type strain in a bioreactor culture. The H2 production rate (191.9 mmol liter−1 h−1 ) and the specific H2 production rate (249.6 mmol g−1 h−1 ) of this strain were extremely high compared with those of CO-dependent H2 -producing prokaryotes reported so far. These results suggest that thecorQR genes encode a positive regulatory protein pair for the expression of a CODH gene cluster. The study also illustrates that manipulation of the transcriptional regulatory system can improve biological H2 production.