Research Article
Effects of the Photosystem II Inhibitors CCCP and DCMU
on Hydrogen Production by the Unicellular Halotolerant
Cyanobacterium Aphanothece halophytica
Sunisa Pansook,
1
Aran Incharoensakdi,
2,3
and Saranya Phunpruch
1,4
1
Department of Biology, Faculty of Science, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, ailand
2
Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science,
Chulalongkorn University, Bangkok 10330, ailand
3
Academy of Science, Royal Society of ailand, Bangkok 10300, ailand
4
Bioenergy Research Unit, Faculty of Science, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10530, ailand
Correspondence should be addressed to Saranya Phunpruch; saranya.ph@kmitl.ac.th
Received 8 February 2019; Revised 3 June 2019; Accepted 11 June 2019; Published 27 June 2019
Academic Editor: Mehmet Yakup Arica
Copyright © 2019 Sunisa Pansook et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
e unicellular halotolerant cyanobacterium Aphanothece halophytica is a potential dark fermentative producer of molecular
hydrogen (H
2
) that produces very little H
2
under illumination. One factor limiting the H
2
photoproduction of this cyanobacterium
is an inhibition of bidirectional hydrogenase activity by oxygen (O
2
) obtained from splitting water molecules via photosystem
II activity. e present study aimed to investigate the effects of the photosystem II inhibitors carbonyl cyanide m-chlorophenyl
hydrazone (CCCP) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on H
2
production of A. halophytica under light and dark
conditions and on photosynthetic and respiratory activities. e results showed that A. halophytica treated with CCCP and DCMU
produced H
2
at three to five times the rate of untreated cells, when exposed to light. e highest H
2
photoproduction rates, 2.26±0.24
and 3.63 ± 0.26 mol H
2
g
−1
dry weight h
−1
, were found in cells treated with 0.5 M CCCP and 50 M DCMU, respectively.
Without inhibitor treatment, A. halophytica incubated in the dark showed a significant increase in H
2
production compared with
cells that were incubated in the light. Only CCCP treatment increased H
2
production of A. halophytica during dark incubation,
because CCCP functions as an uncoupling agent of oxidative phosphorylation. e highest dark fermentative H
2
production rate
of 39.50 ± 2.13 mol H
2
g
−1
dry weight h
−1
was found in cells treated with 0.5 M CCCP aſter 2 h of dark incubation. Under
illumination, CCCP and DCMU inhibited chlorophyll fluorescence, resulting in a low level of O
2
, which promoted bidirectional
hydrogenase activity in A. halophytica cells. In addition, only CCCP enhanced the respiration rate, further reducing the O
2
level.
In contrast, DCMU reduced the respiration rate in A. halophytica.
1. Introduction
Molecular hydrogen (H
2
) has attracted a great deal of interest
from researchers because H
2
combustion liberates a high
heating value with 141.6 MJ kg
−1
[1] and does not emit
polluting gases to the environment. H
2
production is a result
of many processes, including physical, chemical, and biolog-
ical processes. Biological H
2
production can be established
in many kinds of microorganisms such as photosynthetic
bacteria, fermentative bacteria, green algae, and cyanobac-
teria [2]. Among these microorganisms, cyanobacteria show
high capability because they can generate H
2
using electrons
obtained from a light reaction of the photosynthetic pathway
and/or from the degradation of storage carbohydrates within
cells in darkness [3, 4].
e unicellular cyanobacterium Aphanothece halophytica
is a halotolerant microorganism that can grow in a wide
range of salinity from 0.25 to 3.0 M NaCl [5]. A. halophytica
produces a large amount of dark fermentative H
2
compared
with other marine cyanobacteria [6, 7]. H
2
production by
A. halophytica is catalyzed by bidirectional hydrogenase
and occurs particularly under nitrogen-deprived and dark
Hindawi
e Scientific World Journal
Volume 2019, Article ID 1030236, 10 pages
https://doi.org/10.1155/2019/1030236