Role of hydrogenases 3 and 4 in Escherichia coli
growth and H
2
producing hydrogenase activity
during anaerobic utilization of lactose
Satenik Mirzoyan
a
, Armen Trchounian
a,b
, Karen Trchounian
a,*
a
Scientific-Research Institute of Biology, Faculty of Biology, Yerevan State University, 0025 Yerevan, Armenia
b
Department of Biochemistry, Microbiology and Biotechnology, Faculty of Biology, Yerevan State University, 0025
Yerevan, Armenia
article info
Article history:
Received 21 May 2018
Received in revised form
29 July 2018
Accepted 5 August 2018
Available online xxx
Keywords:
Lactose fermentation
H
2
production
Hydrogenases 3 and 4
pH
Escherichia coli
abstract
It is known that Escherichia coli produces hydrogen gas (H
2
) during mixed acid fermentation
via hydrogenase (Hyd) enzymes utilizing sugars, alcohols or organic acids. However, there
are many sugars including lactose which are not studied well. Therefore, H
2
production
and responsible Hyd enzymes activity and role have been investigated. During lactose
fermentation (1e5gL
1
) by E. coli mainly Hyd-4 and partially Hyd-3 have been shown to
affect cell growth and H
2
production at different pHs. At 2 g L
1
lactose fermentation in
hyfG (lacking large subunit of Hyd-4) mutant at pH 5.5 and 6.5 resulted in the decrease of
specific growth rate ~2.5-fold and ~1.8-fold, respectively, compared to wild type. Hyd-3
contribution to cell growth was observed at pH 6.5 with 1 g L
1
and at pH 7.5 with
5gL
1
lactose fermentation. In addition, external pH during 24 or 48 h was less acidified in
hyfG mutant cells grown at pH 6.5 than in wild type. Moreover, the H
2
yield in wild type
cells was 6.00 ± 0.017 mmol L
1
. Hyd-3 and Hyd-4 were responsible for H
2
production at pH
7.5, 6.5 and 5.5, as shown by using hycE (lacking large subunit of Hyd-3) and hyfG single and
hycE hyfB-R (lacking Hyd-3 large subunit and several subunits of Hyd-4) double mutants.
These findings provide novel insights into the H
2
producing activity of E. coli Hyd-3 and
Hyd-4 during utilization of lactose and might be useful for improving H
2
production from
lactose or lactose containing various wastes.
© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction
Under fermentative conditions Escherichia coli and many other
bacteria has the ability to oxidize formate to H
2
and CO
2
. This
process is of great interest to reveal basic mechanisms of
fermentation and find out ways to enhance H
2
production.
The latter is considered as effective, eco-friendly and renew-
able source of energy [1,2] to be used for increased energy
demand. In the last decade investigation of H
2
production
from various biomass had been significantly expanded [3e5];
hence, H
2
generation has advantages e unifies waste utiliza-
tion and energy recovery. Wastes of different origin have been
practiced for production of chemicals or fermentation end
* Corresponding author. Scientific-Research Institute of Biology, Faculty of Biology, Yerevan State University, 1 A. Manoogian Str., 0025
Yerevan, Armenia.
E-mail address: k.trchounian@ysu.am (K. Trchounian).
Available online at www.sciencedirect.com
ScienceDirect
journal homepage: www.elsevier.com/locate/he
international journal of hydrogen energy xxx (2018) 1 e9
https://doi.org/10.1016/j.ijhydene.2018.08.032
0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mirzoyan S, et al., Role of hydrogenases 3 and 4 in Escherichia coli growth and H
2
producing hy-
drogenase activity during anaerobic utilization of lactose, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/
j.ijhydene.2018.08.032