EPSs are very heterogeneous which greatly vary in composition, structure, functional properties, etc. and have got numerous applications in the food, pharmaceutical, cosmetic, nutraceutical, agricultural, and other industries [199]. The market
demand and the scientific interest for these products led to the search for novel EPSs.
Screening studies made so far resulted in the discovery of a vast array of EPS
producing extremophiles including halophiles, psychrophiles, acidophiles, and
alkaliphiles [30].
Microorganisms produce EPSs for various reasons [200]. In alkaliphiles, EPSs
play a vital role in their high pH adaptations that allow them to thrive in their alkaline
habitats. A variety of alkaliphiles such as Cyanospira rippkae and Cyanospira
capsulata are known producing thick EPS capsule [201]. Thus, with further studies,
such alkaliphiles can potentially serve as important sources of EPSs. Probably, the
EPSs of alkaliphiles differ from other groups of microbial EPSs due to their largely
anionic nature. This may indicate the possibility that some alkaliphiles produce
unique EPSs. Indeed, structural studies made so far revealed the presence of novel
EPSs from alkaliphiles [202, 203]. Due to their high density of anions, EPSs from
alkaliphiles have high metal sorption capacity and, hence, can be ideal to trap metal
ions and other cationic pollutants. Thus, the biomass of exopolysaccharide depositing alkaliphilic strains can be used to remove cationic pollutants from industrial
effluents. In this regard, EPS-producing alkaliphilic cyanobacteria have been widely
studied in the removal of heavy metals, and the results indicate their promising
potential [204–206]. EPSs of alkaliphiles have also shown bioflocculant, antioxidant, emulsifying, antivirus, and antitumor properties [207–209] which indicates its
potential in various applications.
4.7 Alkaliphiles in Biofuel Production
Due to environmental concerns and the dwindling of petroleum reserves, the world
has resorted to utilize renewable resources (biomass) to produce fuels. In the
conventional processes of biofuel production, the polymeric biomass is converted
to fermentable sugars which are used by the microbes to make the biofuel. Food and
feed crops such as wheat, sugar beet, sorghum, sugarcane and maize are relatively
easy to hydrolyze to fermentable sugars, and the biofuel production from these
resources can be considered simple, straightforward, and efficient. The biofuels
produced from these kinds of substrates are known as first-generation biofuel.
From economic and environmental point of views, production of first-generation
biofuels is not favorable primarily due to direct competition with food and feed
[210]. Thus, the use of lignocellulosic biomass for production of biofuels has been
promoted. The biofuel produced from agricultural residues or another lignocellulosic
biomass is known as the second-generation biofuel. However, the production of
biofuels from lignocellulosic biomass is not simple. The main challenges in the
second-generation biofuel production process include biomass hydrolysis efficiency,
formation of fermentation inhibitor substances during biomass hydrolysis, risk of
26
G. Mamo and B. Mattiasson
demand and the scientific interest for these products led to the search for novel EPSs.
Screening studies made so far resulted in the discovery of a vast array of EPS
producing extremophiles including halophiles, psychrophiles, acidophiles, and
alkaliphiles [30].
Microorganisms produce EPSs for various reasons [200]. In alkaliphiles, EPSs
play a vital role in their high pH adaptations that allow them to thrive in their alkaline
habitats. A variety of alkaliphiles such as Cyanospira rippkae and Cyanospira
capsulata are known producing thick EPS capsule [201]. Thus, with further studies,
such alkaliphiles can potentially serve as important sources of EPSs. Probably, the
EPSs of alkaliphiles differ from other groups of microbial EPSs due to their largely
anionic nature. This may indicate the possibility that some alkaliphiles produce
unique EPSs. Indeed, structural studies made so far revealed the presence of novel
EPSs from alkaliphiles [202, 203]. Due to their high density of anions, EPSs from
alkaliphiles have high metal sorption capacity and, hence, can be ideal to trap metal
ions and other cationic pollutants. Thus, the biomass of exopolysaccharide depositing alkaliphilic strains can be used to remove cationic pollutants from industrial
effluents. In this regard, EPS-producing alkaliphilic cyanobacteria have been widely
studied in the removal of heavy metals, and the results indicate their promising
potential [204–206]. EPSs of alkaliphiles have also shown bioflocculant, antioxidant, emulsifying, antivirus, and antitumor properties [207–209] which indicates its
potential in various applications.
4.7 Alkaliphiles in Biofuel Production
Due to environmental concerns and the dwindling of petroleum reserves, the world
has resorted to utilize renewable resources (biomass) to produce fuels. In the
conventional processes of biofuel production, the polymeric biomass is converted
to fermentable sugars which are used by the microbes to make the biofuel. Food and
feed crops such as wheat, sugar beet, sorghum, sugarcane and maize are relatively
easy to hydrolyze to fermentable sugars, and the biofuel production from these
resources can be considered simple, straightforward, and efficient. The biofuels
produced from these kinds of substrates are known as first-generation biofuel.
From economic and environmental point of views, production of first-generation
biofuels is not favorable primarily due to direct competition with food and feed
[210]. Thus, the use of lignocellulosic biomass for production of biofuels has been
promoted. The biofuel produced from agricultural residues or another lignocellulosic
biomass is known as the second-generation biofuel. However, the production of
biofuels from lignocellulosic biomass is not simple. The main challenges in the
second-generation biofuel production process include biomass hydrolysis efficiency,
formation of fermentation inhibitor substances during biomass hydrolysis, risk of
26
G. Mamo and B. Mattiasson