title: Citrobacter amalonaticusY19 for constitutive expression of carbon monoxide-dependent hydrogen-production machinery.
abstract: BACKGROUND
  Citrobacter amalonaticusY19 is a good biocatalyst for production of hydrogen (H2) from oxidation of carbon monoxide (CO) via the so-called water-gas-shift reaction (WGSR). It has a high H2-production activity (23.83 mmol H2g-1cell h-1) from CO, and can grow well to a high density on various sugars. However, its H2-production activity is expressed only when CO is present as an inducer and in the absence of glucose.
  
  
  RESULTS
  In order to avoid dependency on CO and glucose, in the present study, the native CO-inducible promoters of WGSR operons (CO dehydrogenase, CODH, and CODH-dependent hydrogenase, CO-hyd) in Y19 were carefully analyzed and replaced with strong and constitutive promoters screened from Y19. One engineered strain (Y19-PR1), selected from three positive ones after screening ~10,000 colonies, showed a similar CO-dependent H2-production activity to that of wild-type Y19, without being affected by glucose and/or CO. Compared with wild-type Y19, transcription of the CODH operon in Y19-PR1 increased 1.5-fold, although that of the CO-hydoperon remained at a similar level. To enhance the activity of CO-Hyd in Y19-PR1, further modifications, including an increase in gene copy number and engineering of the 5' untranslated region, were attempted, but without success.
  
  
  CONCLUSIONS
  Convenient recombinant Y19-PR1 that expresses CO-dependent H2-production activity without being limited by CO and glucose was obtained.
authors.affiliation: School of Chemical and Biomolecular Engineering, Pusan National University, San 30, Jangeon-dong, Geumjeong-gu, Busan, 609-735 Republic of Korea.
authors.forename: Satish Kumar
authors.initials: SK
authors.lastname: Ainala
authors.affiliation: School of Chemical and Biomolecular Engineering, Pusan National University, San 30, Jangeon-dong, Geumjeong-gu, Busan, 609-735 Republic of Korea.
authors.forename: Eunhee
authors.initials: E
authors.lastname: Seol
authors.affiliation: School of Chemical and Biomolecular Engineering, Pusan National University, San 30, Jangeon-dong, Geumjeong-gu, Busan, 609-735 Republic of Korea.
authors.forename: Jung Rae
authors.initials: JR
authors.lastname: Kim
authors.affiliation: School of Chemical and Biomolecular Engineering, Pusan National University, San 30, Jangeon-dong, Geumjeong-gu, Busan, 609-735 Republic of Korea.
authors.forename: Sunghoon
authors.initials: S
authors.lastname: Park
keywords: CO-Hyd; CODH; Citrobacter amalonaticus; Water–gas-shift reaction; gapA; narG