cutting down the operating cost involved in separate processes. Also, enzymes that
are able to tolerate higher temperatures promote faster reactions, allow high solubility of the substrate, and also lower the viscosity of solution, thereby enhancing the
solvent’s mixability. Thermophiles possess many additional benefits such as wide
spectrum of substrates, thereby allowing them to go for simultaneous degradation of
both hexoses and pentoses; some thermophiles are inherently robust to break down
complex carbohydrates. Use of thermophiles enables a one-step operation of enzymatic breakdown, fermentation, and distillation of formed ethanol (Xiao et al. 2012).
3.5
Habitat of Thermophiles
Thermophiles can potentially grow at temperatures of 55
C or more than this. The
minimum temperature necessary for their growth is usually around 45
C, and they
often have optimum temperature in the range of 55–65
C. Majority of prokaryotes
and some of the algae and fungi are thermophiles. Habitats like composts, selfheating haystacks, hot water lines, and hot springs are best suited for their propagation. These organisms possess enzymes that are stable at high temperature as well as
machineries of protein synthesis are capable of functioning even at elevated temperature. These features make thermophiles different from mesophiles. Lipids present in
membranes of thermophiles are highly saturated and possess elevated melting
points. It is due to this property that the membranes of these organisms remain in
their configuration at higher temperature. Hyperthermophiles cannot grow well
below 55
C, as their optimal temperature toward cultivation lies in the range of
80–113
C. There are few hyperthermophiles like Pyrococcus abyssi and
Pyrodictium occultum, which are able to exist in hot areas of the seafloor. Sulfide
chimneys or “black smokers” are also a well-known habitat for thermophiles. The
temperature of superheated vent water, which is rich in sulfide is about 350
C.
These microbes can grow and reproduce at 113
C. Seawater does not boil until
460
C, as the pressure found in these habitats is about 265 atm, which is responsible
for keeping water at liquid state. Crenarchaeota are the thermophiles that are not only
acidophiles but sulfur dependent too. Sulfur serves as an electron acceptor in
anaerobic respiration or as an electron source by lithotrophs. Solfatara are the
habitats where hot springs are found, which are sulfur enriched in Yellowstone
National Park, Wyoming. Solfatara also include the waters surrounding areas of
submarine volcanic activity. Solfatara are also fields of elevated temperature found
within zones of volcanic activity, with high sulfur acidic soil, acidic hot springs, and
boiling mud. Thermophiles can grow in soils rich in sulfur as well as in geothermally
heated water. Almost all thermophiles are anaerobes.
The photosynthetic bacteria such as cyanobacteria, green, and purple bacteria are
the examples of the thermophile marine microorganisms. The prominent bacterial
domains that are thermophiles include Actinobacteria sp., Bacillus sp., Clostridium
sp., Desulfotomaculum sp., Thermus sp., Thiobacillus sp., fermenting bacteria,
spirochetes, and numerous other genera. The archaea domains such as Pyrococcus
sp., Sulfolobus sp., Thermococcus sp., Thermoplasma sp., and methanogens are also
3 Role of Thermophiles in Production of Aviation Biofuels: Fueling the Future
73
are able to tolerate higher temperatures promote faster reactions, allow high solubility of the substrate, and also lower the viscosity of solution, thereby enhancing the
solvent’s mixability. Thermophiles possess many additional benefits such as wide
spectrum of substrates, thereby allowing them to go for simultaneous degradation of
both hexoses and pentoses; some thermophiles are inherently robust to break down
complex carbohydrates. Use of thermophiles enables a one-step operation of enzymatic breakdown, fermentation, and distillation of formed ethanol (Xiao et al. 2012).
3.5
Habitat of Thermophiles
Thermophiles can potentially grow at temperatures of 55
C or more than this. The
minimum temperature necessary for their growth is usually around 45
C, and they
often have optimum temperature in the range of 55–65
C. Majority of prokaryotes
and some of the algae and fungi are thermophiles. Habitats like composts, selfheating haystacks, hot water lines, and hot springs are best suited for their propagation. These organisms possess enzymes that are stable at high temperature as well as
machineries of protein synthesis are capable of functioning even at elevated temperature. These features make thermophiles different from mesophiles. Lipids present in
membranes of thermophiles are highly saturated and possess elevated melting
points. It is due to this property that the membranes of these organisms remain in
their configuration at higher temperature. Hyperthermophiles cannot grow well
below 55
C, as their optimal temperature toward cultivation lies in the range of
80–113
C. There are few hyperthermophiles like Pyrococcus abyssi and
Pyrodictium occultum, which are able to exist in hot areas of the seafloor. Sulfide
chimneys or “black smokers” are also a well-known habitat for thermophiles. The
temperature of superheated vent water, which is rich in sulfide is about 350
C.
These microbes can grow and reproduce at 113
C. Seawater does not boil until
460
C, as the pressure found in these habitats is about 265 atm, which is responsible
for keeping water at liquid state. Crenarchaeota are the thermophiles that are not only
acidophiles but sulfur dependent too. Sulfur serves as an electron acceptor in
anaerobic respiration or as an electron source by lithotrophs. Solfatara are the
habitats where hot springs are found, which are sulfur enriched in Yellowstone
National Park, Wyoming. Solfatara also include the waters surrounding areas of
submarine volcanic activity. Solfatara are also fields of elevated temperature found
within zones of volcanic activity, with high sulfur acidic soil, acidic hot springs, and
boiling mud. Thermophiles can grow in soils rich in sulfur as well as in geothermally
heated water. Almost all thermophiles are anaerobes.
The photosynthetic bacteria such as cyanobacteria, green, and purple bacteria are
the examples of the thermophile marine microorganisms. The prominent bacterial
domains that are thermophiles include Actinobacteria sp., Bacillus sp., Clostridium
sp., Desulfotomaculum sp., Thermus sp., Thiobacillus sp., fermenting bacteria,
spirochetes, and numerous other genera. The archaea domains such as Pyrococcus
sp., Sulfolobus sp., Thermococcus sp., Thermoplasma sp., and methanogens are also
3 Role of Thermophiles in Production of Aviation Biofuels: Fueling the Future
73