Hydrogen production by Escherichia coli during glucose fermentation: Effects of oxidative and reductive routes used by the strain lacking hydrogen oxidizing hydrogenases 1(hya) and 2 (hyb) Varduhi Abrahamyan a , Anna Poladyan a,b,* , Anait Vassilian c , Armen Trchounian a a Department of Microbiology & Plants and Microbes Biotechnology, Biology Faculty, Yerevan State University, 1 A. Manoogian Str, 0025 Yerevan, Armenia b Department of Biophysics, Biology Faculty, Yerevan State University, 1 A. Manoogian Str, 0025 Yerevan, Armenia c Department of Ecology and Nature Protection, Biology Faculty, Yerevan State University, 1 A. Manoogian Str, 0025 Yerevan, Armenia article info Article history: Received 27 August 2014 Received in revised form 27 January 2015 Accepted 1 February 2015 Available online 25 February 2015 Keywords: Hydrogenases Hydrogen production Redox potential Fermentation pH Escherichia coli abstract Changes in oxidationereduction potential (ORP) values during Escherichia coli DhyaB DhybC double mutant lacking of large subunits of hydrogenases 1 (Hyd-1) and 2 (Hyd-2) and ef- fects of redox reagents were studied upon glucose fermentation at acidic (5.5) and alkaline (7.5) pHs. H 2 production yield was determined by the readings of platinum and titanium- silicate electrodes. Specific growth rate of mutant was inhibited by ~1.3 fold at pH 5.5 in the presence of membrane-permeating reducing agent DL-dithiothreitol (DTT) and impermeable oxidant potassium ferricyanide (K 3 [Fe(CN) 6 ]), whereas at pH 7.5 the reagents had no significant effects. H 2 production was stimulated by ~1.4 fold with mutant compared to the wild type at pH 7.5. Moreover, 3 mM DTT stimulated H 2 production yield by ~2 and ~4 fold during bacterial log growth phase at pH 5.5 and pH 7.5, respectively. While at pH 5.5 1 mM K 3 [Fe(CN) 6 ] completely inhibited H 2 formation by mutant as well as wild type resulting in alternation of ORP to positive values (200 ± 10 mV) at the end of log growth phase. At pH 7.5H 2 formation by the wild type was inhibited by ~1.2 fold, while in the case of mutant H 2 formation was completely inhibited, but resulting in decrease of ORP to negative values (270 ± 12 mV) at the end of log growth phase. These findings point out the effects of lacked Hyd-1 and Hyd-2 both on H 2 production by E. coli and indicate the importance of reductive conditions for enhanced H 2 production as well. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. * Corresponding author. Department of Microbiology & Plants and Microbes Biotechnology, Yerevan State University, 1 A. Manoogian Str, 0025 Yerevan, Armenia. Tel.: þ374 60710519. E-mail address: APoladyan@ysu.am (A. Poladyan). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 40 (2015) 7459 e7464 http://dx.doi.org/10.1016/j.ijhydene.2015.02.006 0360-3199/Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.