A novel co-responsive transcriptional regulator and enhanced H₂ production by an engineered Thermococcus onnurineus NA1 strain

Genome analysis revealed the existence of a putative transcriptional regulatory system governing CO metabolism in Thermococcus 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 of Thermococcus species and "Candidatus Korarchaeum cryptofilum" OPF8. In-frame deletion of either corQ or corR caused a severe impairment in CO-dependent growth and H₂ production. When corQ and corR deletion mutants were complemented by introducing the corQR 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 integrated corQR (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 the corQR 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.