title: Increasing the metabolic capacity of Escherichia coli for hydrogen production through heterologous expression of the Ralstonia eutropha SH operon.
abstract: BACKGROUND
  Fermentative hydrogen production is an attractive means for the sustainable production of this future energy carrier but is hampered by low yields. One possible solution is to create, using metabolic engineering, strains which can bypass the normal metabolic limits to substrate conversion to hydrogen. Escherichia coli can degrade a variety of sugars to hydrogen but can only convert electrons available at the pyruvate node to hydrogen, and is unable to use the electrons available in NADH generated during glycolysis.
  
  
  RESULTS
  Here, the heterologous expression of the soluble [NiFe] hydrogenase from Ralstonia eutropha H16 (the SH hydrogenase) was used to demonstrate the introduction of a pathway capable of deriving substantial hydrogen from the NADH generated by fermentation. Successful expression was demonstrated by in vitro assay of enzyme activity. Moreover, expression of SH restored anaerobic growth on glucose to adhE strains, normally blocked for growth due to the inability to re-oxidize NADH. Measurement of in vivo hydrogen production showed that several metabolically engineered strains were capable of using the SH hydrogenase to derive 2 mol H2 per mol of glucose consumed, close to the theoretical maximum.
  
  
  CONCLUSIONS
  Previous introduction of heterologous [NiFe] hydrogenase in E. coli led to NAD(P)H dependent activity, but hydrogen production levels were very low. Here we have shown for the first time substantial in vivo hydrogen production by a heterologously expressed [NiFe] hydrogenase, the soluble NAD-dependent H2ase of R. eutropha (SH hydrogenase). This hydrogenase was able to couple metabolically generated NADH to hydrogen production, thus rescuing an alcohol dehydrogenase (adhE) mutant. This enlarges the range of metabolism available for hydrogen production, thus potentially opening the door to the creation of greatly improved hydrogen production. Strategies for further increasing yields should revolve around making additional NADH available.
authors: Département de Microbiologie et Immunologie, Université de Montréal, CP 6128 Succursale Centre-ville, Montréal, Québec, Canada H3C 3J7. patrick.hallenbeck@umontreal.ca.
authors: Dipankar
authors: D
authors: Ghosh
authors: Ariane
authors: A
authors: Bisaillon
authors: Patrick C
authors: PC
authors: Hallenbeck
references: Microbiology (Reading). 2011 May;157(Pt 5):1363-1374
references: 21349975
references: Adv Microb Physiol. 2006;51:1-71
references: 17091562
references: Chem Rev. 2007 Oct;107(10):4206-72
references: 17927159
references: J Bacteriol. 2004 Jan;186(2):580-7
references: 14702328
references: J Bacteriol. 2005 May;187(9):3122-32
references: 15838039
references: Bioresour Technol. 2012 Apr;110:1-9
references: 22342581
references: Metab Eng. 2009 May;11(3):139-47
references: 19558967
references: J Bacteriol. 1981 Mar;145(3):1144-9
references: 6782086
references: J Bacteriol. 1996 Apr;178(8):2368-74
references: 8636040
references: J Bacteriol. 1989 Jul;171(7):3650-5
references: 2661531
references: Trends Biotechnol. 2009 May;27(5):287-97
references: 19329204
references: Dalton Trans. 2009 Dec 7;(45):9970-8
references: 19904422
references: PLoS One. 2010 May 06;5(5):e10526
references: 20463892
references: Bioresour Technol. 2010 Mar;101(6):1820-5
references: 19897361
references: Bioresour Technol. 2011 Sep;102(18):8357-67
references: 21733680
references: J Bacteriol. 1990 Jun;172(6):2920-9
references: 2188945
references: Arch Mikrobiol. 1961;38:209-22
references: 13747777
references: Arch Microbiol. 1998 Nov;170(6):451-9
references: 9799289
references: Bioresour Technol. 2011 Sep;102(18):8414-22
references: 21470849
references: Curr Issues Mol Biol. 2004 Jul;6(2):159-88
references: 15119826
references: J Bacteriol. 2002 Dec;184(23):6642-53
references: 12426353
references: Microb Cell Fact. 2012 Aug 27;11:115
references: 22925149
references: Microb Biotechnol. 2008 Sep;1(5):382-94
references: 21261858
references: J Bacteriol. 1981 Feb;145(2):1110-1
references: 7007341
references: Metab Eng. 2011 Jul;13(4):445-53
references: 21276867
references: Dalton Trans. 2009 Jun 14;(22):4274-85
references: 19662302
references: J Bacteriol. 1991 Aug;173(15):4851-61
references: 1856178
references: Microb Cell Fact. 2012 Jan 04;11:2
references: 22217184
references: Biotechnol Bioeng. 2011 Dec;108(12):2941-6
references: 21732330
references: Biochim Biophys Acta. 1976 Nov 8;452(1):66-80
references: 186126
references: J Biotechnol. 2011 Sep 20;155(3):312-9
references: 21794837
references: J Bacteriol. 1998 Jun;180(12):3197-204
references: 9620971