glycine [GalpA(Gly)]. The following linear structure of the repeating unit was
established:
!3)-α-D-GalpA(Gly)-(1!4)-β-D-ManpNAcA-(1!4)-α-D-GalpA(1!3)-α-D-QuipNAc4NAc-(1! [92]. The gross chemical composition of the
EPS, produced by halophilic bacterium Vagococcus carniphilus from alkaline
Lonar Lake, India, indicated content of 20% of protein and 75% neutral sugars.
The monosaccharide composition revealed the presence of galactose and mannose
with an additional three unidentified compounds. FTIR analysis confirmed the
presence of an alkyl groups in the polysaccharide and a 75% similarity with standard
dextran. The organism produced 1.1 g/L of EPS under optimized conditions [93].
Isolated from the radon hot spring, a thermophilic, endospore-forming, and
radiation-resistant bacterium Geobacillus sp. produced an exopolysaccharide with
the average molecular weight 3.2 Â 10
6 Da and exhibited maximum growth at 60
C
and pH 8.0. The EPS was a heteropolysaccharide, composed of mainly D-mannose,
D-glucose, and rhamnose. The uronic acids and acetyl contents were at 18.6% and
6.1%, respectively. The EPS demonstrated good antioxidant activities and restrained
proliferation of hepatoma carcinoma cells [86]. A thermophilic haloalkaliphilic
Bacillus licheniformis strain, produced a novel 1,000 kDa exopolysaccharide. In
particular, EPS1 displayed a high carbohydrate content (99%) with fructose and
fucose as the major monosaccharides, low content of protein (1.2%), and 0.5% of
uronic acid. Due to its structure, it could be a convenient thickener in industrial
products. Under optimal growth conditions (50
C; pH 8 and 5% (w/v) NaCl), a
366 mg/L EPS production was achieved after 48 h of cultivation. The EPS was stable
and exhibit decomposition at very high temperature, 240
C. Screening for biological
activity showed its cytoprotective effect against Avarol in the brine shrimp test,
indicating a potential use in the development of novel drugs [85]. Another thermostable EPS that degrades at a very high temperature (290
C) has been reported from
haloalkaliphilic Bacillus sp. The amount of neutral sugars, uronic acid, and amino
sugars were 52.4, 17.2, and 2.4%, respectively. Heteroglucan with Mw 2.2 Â 10
6 Da
had considerable flocculation activity and high gel strength [94]. The EPS produced
by haloalkaliphilic Methylophaga murata Kr3 was composed of carbohydrate and
protein moieties that could stabilize the cells and prevent them from drying
[88]. Strain Kr3T represents a promising candidate for cost-effective large-scale
production of EPS as the result of the ability to use methanol, methylamine,
trimethylamine, and fructose as carbon and energy sources under a wide range of
pHs and salinities.
The limitation for commercial applications of alkaliphiles EPS is associated with
the lack of proper large-scale production. Overcoming such constrains by process
development and with more proper bioreactor design specific for alkaliphiles will
help in the commercialization of EPSs from alkaliphiles. Most probably, metabolic
engineering of the alkaliphiles will be also required. Abundant EPSs production is
often induced by special factors in the nutritional conditions (often a lack of a
nutrient). This is controversial in increasing the production. While EPSs protect
microbes, they can also prevent them to access to low-molecular opportunistic
nutrient sources.
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
179
established:
!3)-α-D-GalpA(Gly)-(1!4)-β-D-ManpNAcA-(1!4)-α-D-GalpA(1!3)-α-D-QuipNAc4NAc-(1! [92]. The gross chemical composition of the
EPS, produced by halophilic bacterium Vagococcus carniphilus from alkaline
Lonar Lake, India, indicated content of 20% of protein and 75% neutral sugars.
The monosaccharide composition revealed the presence of galactose and mannose
with an additional three unidentified compounds. FTIR analysis confirmed the
presence of an alkyl groups in the polysaccharide and a 75% similarity with standard
dextran. The organism produced 1.1 g/L of EPS under optimized conditions [93].
Isolated from the radon hot spring, a thermophilic, endospore-forming, and
radiation-resistant bacterium Geobacillus sp. produced an exopolysaccharide with
the average molecular weight 3.2 Â 10
6 Da and exhibited maximum growth at 60
C
and pH 8.0. The EPS was a heteropolysaccharide, composed of mainly D-mannose,
D-glucose, and rhamnose. The uronic acids and acetyl contents were at 18.6% and
6.1%, respectively. The EPS demonstrated good antioxidant activities and restrained
proliferation of hepatoma carcinoma cells [86]. A thermophilic haloalkaliphilic
Bacillus licheniformis strain, produced a novel 1,000 kDa exopolysaccharide. In
particular, EPS1 displayed a high carbohydrate content (99%) with fructose and
fucose as the major monosaccharides, low content of protein (1.2%), and 0.5% of
uronic acid. Due to its structure, it could be a convenient thickener in industrial
products. Under optimal growth conditions (50
C; pH 8 and 5% (w/v) NaCl), a
366 mg/L EPS production was achieved after 48 h of cultivation. The EPS was stable
and exhibit decomposition at very high temperature, 240
C. Screening for biological
activity showed its cytoprotective effect against Avarol in the brine shrimp test,
indicating a potential use in the development of novel drugs [85]. Another thermostable EPS that degrades at a very high temperature (290
C) has been reported from
haloalkaliphilic Bacillus sp. The amount of neutral sugars, uronic acid, and amino
sugars were 52.4, 17.2, and 2.4%, respectively. Heteroglucan with Mw 2.2 Â 10
6 Da
had considerable flocculation activity and high gel strength [94]. The EPS produced
by haloalkaliphilic Methylophaga murata Kr3 was composed of carbohydrate and
protein moieties that could stabilize the cells and prevent them from drying
[88]. Strain Kr3T represents a promising candidate for cost-effective large-scale
production of EPS as the result of the ability to use methanol, methylamine,
trimethylamine, and fructose as carbon and energy sources under a wide range of
pHs and salinities.
The limitation for commercial applications of alkaliphiles EPS is associated with
the lack of proper large-scale production. Overcoming such constrains by process
development and with more proper bioreactor design specific for alkaliphiles will
help in the commercialization of EPSs from alkaliphiles. Most probably, metabolic
engineering of the alkaliphiles will be also required. Abundant EPSs production is
often induced by special factors in the nutritional conditions (often a lack of a
nutrient). This is controversial in increasing the production. While EPSs protect
microbes, they can also prevent them to access to low-molecular opportunistic
nutrient sources.
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
179