hydrolysate, it is possible to control the fermentation without pumping base. Moreover, in mixed culture system, better ethanol production has been reported at higher
pH [215, 216].
The second possibility of alkaliphiles in biofuel production is their use as biofuel
producers. In fact, this approach allows direct utilization of alkaline hydrolysate, and
it is attractive from economic as well as technical stand. Bacillus marmarensis, an
obligate alkaliphile that grows optimally at pH 10, was used as model organism in an
effort of evaluating the true potential of alkaliphiles in biorefineries. An engineered
B. marmarensis is reportedly producing 38 g/l ethanol at yield of 65% using glucose
as carbon source in unsterilized media at very high pH [217]. These authors also
indicated that the alkaliphile can produce ethanol from xylose and cellobiose at a
titer of 12 g/l and 50% yield in media prepared with unsterilized seawater. This
approach of successfully running unsterilized fermentation indicates the possibility
of contamination-resistant biorefining which utilizes pentoses and disaccharides
using alkaliphiles. The approach has a great potential in minimizing the biofuel
production cost. In addition to bioethanol production, alkaliphiles have been also
used successfully to produce biohydrogen [218] and biogas [219].
The third possibility of using alkaliphiles in biofuel production is related to
biodiesel. Certain alkaliphilic organisms accumulate lipid which can be of interest
for biodiesel production. Lipogenic alkaliphiles such as Neochloris oleoabundans
[220] and Chlorella vulgaris BA050 [221] accumulate high amount of lipids.
Studies have indicated that biodiesel production using these kinds of alkaliphilic
lipogenic organisms could be energy efficient [222]. Although outdoor cultivation
can significantly reduce the production cost, cultivating of non-alkaliphiles is often
challenged by poor economic feasibility due to the high cost of CO 2 supply and
contamination problems [223]. On the other hand, unlike non-alkaliphiles, the
outdoor cultivation of alkaliphilic algae is very attractive for production of biofuels.
This is due to the high pH growth condition which promotes CO 2 solubility and
avoids the need for CO 2 sparging. Moreover, the high pH heavily minimizes the
possibility of contamination and further promotes the economic viability [221].
4.8 Organic Acids
Organic acids are versatile substances with a wide range of applications in several
industries such as in food, beverage, feed, chemicals, personal care and pharmaceuticals. Commercially, these valuable compounds are produced through multi-step
chemical synthesis from petroleum-based resources or by microbial fermentation.
Compared to the chemical synthesis route, the microbial production approach has
several advantages including high purity, enantioselectivity, cost-efficiency and its
environmental benign nature.
Organic acid production is among the adaptive strategies deployed by alkaliphiles
to thrive in high pH habitats. This ability of alkaliphiles can be potentially attractive
for commercial production of organic acids. So far, the studies in this regard are
28
G. Mamo and B. Mattiasson
pH [215, 216].
The second possibility of alkaliphiles in biofuel production is their use as biofuel
producers. In fact, this approach allows direct utilization of alkaline hydrolysate, and
it is attractive from economic as well as technical stand. Bacillus marmarensis, an
obligate alkaliphile that grows optimally at pH 10, was used as model organism in an
effort of evaluating the true potential of alkaliphiles in biorefineries. An engineered
B. marmarensis is reportedly producing 38 g/l ethanol at yield of 65% using glucose
as carbon source in unsterilized media at very high pH [217]. These authors also
indicated that the alkaliphile can produce ethanol from xylose and cellobiose at a
titer of 12 g/l and 50% yield in media prepared with unsterilized seawater. This
approach of successfully running unsterilized fermentation indicates the possibility
of contamination-resistant biorefining which utilizes pentoses and disaccharides
using alkaliphiles. The approach has a great potential in minimizing the biofuel
production cost. In addition to bioethanol production, alkaliphiles have been also
used successfully to produce biohydrogen [218] and biogas [219].
The third possibility of using alkaliphiles in biofuel production is related to
biodiesel. Certain alkaliphilic organisms accumulate lipid which can be of interest
for biodiesel production. Lipogenic alkaliphiles such as Neochloris oleoabundans
[220] and Chlorella vulgaris BA050 [221] accumulate high amount of lipids.
Studies have indicated that biodiesel production using these kinds of alkaliphilic
lipogenic organisms could be energy efficient [222]. Although outdoor cultivation
can significantly reduce the production cost, cultivating of non-alkaliphiles is often
challenged by poor economic feasibility due to the high cost of CO 2 supply and
contamination problems [223]. On the other hand, unlike non-alkaliphiles, the
outdoor cultivation of alkaliphilic algae is very attractive for production of biofuels.
This is due to the high pH growth condition which promotes CO 2 solubility and
avoids the need for CO 2 sparging. Moreover, the high pH heavily minimizes the
possibility of contamination and further promotes the economic viability [221].
4.8 Organic Acids
Organic acids are versatile substances with a wide range of applications in several
industries such as in food, beverage, feed, chemicals, personal care and pharmaceuticals. Commercially, these valuable compounds are produced through multi-step
chemical synthesis from petroleum-based resources or by microbial fermentation.
Compared to the chemical synthesis route, the microbial production approach has
several advantages including high purity, enantioselectivity, cost-efficiency and its
environmental benign nature.
Organic acid production is among the adaptive strategies deployed by alkaliphiles
to thrive in high pH habitats. This ability of alkaliphiles can be potentially attractive
for commercial production of organic acids. So far, the studies in this regard are
28
G. Mamo and B. Mattiasson