bacteria do not retain their viability after alkaline and heat pretreatment because of
the high concentration of Na
+ ions, as the acidogenesis process in anaerobic digestion is severely inhibited by such conditions [9]. Therefore, an additional step to
dilute or neutralize the alkaline conditions is required before proceeding to the next
step of fermentative hydrogen production. However, this additional step makes the
whole process less economical. One way to overcome this problem is by utilizing
extremely halotolerant hydrogen-producing bacteria in dark fermentation process.
These bacteria are advantageous for developing “Next Generation Industrial Biotechnology” (NGIB) as they cut the costs of freshwater, oxygen, and
sterilization [10].
In the past few years, several studies have investigated hydrogen production
using halotolerant and halophilic bacteria in dark fermentation process. Most of
these studies focused mainly on pure cultures in a moderate halophilic environment
with a salt concentration of 0.5 M (25 g/L) to 2.5 M (150 g/L), although one research
also investigated mixed cultures. Liaw and Mah [11] mentioned the production of
144.5 μmol hydrogen from 5 mL medium with 12% NaCl and 0.5% glucose at 37
C
by Haloanaerobacter chitinovorans sp. nov., while Mouné et al. [12] found that
Haloanaerobacter salinarius sp. nov. was able to produce 2 mM hydrogen from
4.17 mM glucose substrate in 14–15% NaCl, 45
C, and pH 7.4–7.8. Matsumura
et al. [13] discussed the production of 1.7-mol H 2 /mol mannitol by Vibrio tritonius
strain AM2 at initial 2.25% (w/v) NaCl, pH 6, and 37
C.
Kivistö et al. [14] reported that H. saccharolyticum subspecies saccharolyticum
produced 0.6-mol H 2 /mol glycerol at a salt concentration of 150 g/L (2.6 M), pH of
7.4, temperature of 37
C, and glycerol concentration of 2.5 g/L, while
H. saccharolyticum subspecies senegalensis produced 1.6 mol H 2 /mol glycerol at
pH 7.0. Brown et al. [15] found that H. hydrogeniformans was capable of producing
hydrogen at a pH of 11, 7% (wt./vol.) NaCl, and 33
C. Pierra et al. [16] described
the ability of a mixed culture affiliated to the family of Vibrionaceae to produce
0.9 Æ 0.02 mol H 2 /mol glucose at initial pH of 8 and temperature of 35
C under a
moderate halophilic environment (75 g/L NaCl). To date, no studies have investigated hydrogen production under conditions of a high salinity of 26% (6 M or
351.35 g/L NaCl).
This research aims to investigate hydrogen production from lignocellulosic
biomass by extremely halotolerant bacteria. The hypothesis is that extremely
halotolerant hydrogen-producing bacteria can tolerate high concentrations of Na
+
ions. Based on this hypothesis, hydrogen production under different salinity concentrations before and after acclimatization was evaluated. The bacteria’s requirement for chloride ions in high salinity conditions was also investigated. In addition,
it will be discussed about the suitability of our isolated extremely halotolerant
bacteria for hydrogen production from lignocellulosic biomass.
414
D. A. H. Taroepratjeka et al.
the high concentration of Na
+ ions, as the acidogenesis process in anaerobic digestion is severely inhibited by such conditions [9]. Therefore, an additional step to
dilute or neutralize the alkaline conditions is required before proceeding to the next
step of fermentative hydrogen production. However, this additional step makes the
whole process less economical. One way to overcome this problem is by utilizing
extremely halotolerant hydrogen-producing bacteria in dark fermentation process.
These bacteria are advantageous for developing “Next Generation Industrial Biotechnology” (NGIB) as they cut the costs of freshwater, oxygen, and
sterilization [10].
In the past few years, several studies have investigated hydrogen production
using halotolerant and halophilic bacteria in dark fermentation process. Most of
these studies focused mainly on pure cultures in a moderate halophilic environment
with a salt concentration of 0.5 M (25 g/L) to 2.5 M (150 g/L), although one research
also investigated mixed cultures. Liaw and Mah [11] mentioned the production of
144.5 μmol hydrogen from 5 mL medium with 12% NaCl and 0.5% glucose at 37
C
by Haloanaerobacter chitinovorans sp. nov., while Mouné et al. [12] found that
Haloanaerobacter salinarius sp. nov. was able to produce 2 mM hydrogen from
4.17 mM glucose substrate in 14–15% NaCl, 45
C, and pH 7.4–7.8. Matsumura
et al. [13] discussed the production of 1.7-mol H 2 /mol mannitol by Vibrio tritonius
strain AM2 at initial 2.25% (w/v) NaCl, pH 6, and 37
C.
Kivistö et al. [14] reported that H. saccharolyticum subspecies saccharolyticum
produced 0.6-mol H 2 /mol glycerol at a salt concentration of 150 g/L (2.6 M), pH of
7.4, temperature of 37
C, and glycerol concentration of 2.5 g/L, while
H. saccharolyticum subspecies senegalensis produced 1.6 mol H 2 /mol glycerol at
pH 7.0. Brown et al. [15] found that H. hydrogeniformans was capable of producing
hydrogen at a pH of 11, 7% (wt./vol.) NaCl, and 33
C. Pierra et al. [16] described
the ability of a mixed culture affiliated to the family of Vibrionaceae to produce
0.9 Æ 0.02 mol H 2 /mol glucose at initial pH of 8 and temperature of 35
C under a
moderate halophilic environment (75 g/L NaCl). To date, no studies have investigated hydrogen production under conditions of a high salinity of 26% (6 M or
351.35 g/L NaCl).
This research aims to investigate hydrogen production from lignocellulosic
biomass by extremely halotolerant bacteria. The hypothesis is that extremely
halotolerant hydrogen-producing bacteria can tolerate high concentrations of Na
+
ions. Based on this hypothesis, hydrogen production under different salinity concentrations before and after acclimatization was evaluated. The bacteria’s requirement for chloride ions in high salinity conditions was also investigated. In addition,
it will be discussed about the suitability of our isolated extremely halotolerant
bacteria for hydrogen production from lignocellulosic biomass.
414
D. A. H. Taroepratjeka et al.