attachment to get long fibers possibly capped by a specific attachment protein
[78]. Without the property to the firm attachment, a microbe cannot be pathogenic,
as known from pathogenic and nonpathogenic E. coli strains. EPSs could provide an
evident survival mechanism to extremophiles for making capsules around the cells
and for binding to surfaces for propagation. Structures of EPSs vary and constitute a
wide spectrum of properties.
EPSs biosynthesis can take place either fully extracellularly or partly intracellularly and partly extracellularly. Glycosyltransferase enzymes make the complicated
transfers of sugar units in the growing polymer system. EPSs and their structures,
analysis, biosynthesis, and properties from extremophiles are reviewed in detail
[79]. Alkaliphiles have unusual structures of EPSs. Many haloalkaliphiles strains
produce more than one different EPS [79]. Natural or chemically functionalized
carbohydrates are important biotechnological products in industry as gelling agents,
thickeners, or edible films. EPSs also have multifarious biotechnological applications in food and pharmaceutical industries. Microbial EPSs could add to the
spectrum of related gum-like substances of non-microbial origin. Food industry is
strictly limited to certain accepted nonpathogenic producer strains. This limitation
does not apply to other technical applications where the product repertoire may thus
be much bigger.
Cyclodextrins (CDs) are ring-shaped glucose oligomers (6, 7, or 8 glucose units)
derived from starch by the enzyme cyclomaltodextrin glucanotransferase, CGTase
([80]; a review). Formally, CGTases are messengers of the cells, like any enzymes or
EPSs aimed at acquiring better living conditions for a microbe. There was for a long
time conception that there are separate enzymes for the different CD rings. It was
convincingly shown that there is only one enzyme by purifying CGTase from an
alkaliphilic Bacillus to an extremely homogenous stage on the immobiline
electrofocusing. There were microheterogenic fractions (one or two charge differences), but the CD profile was the same [81, 82]. However, the reaction conditions
affect the equilibrium between acyclic and cyclic forms of CDs, a low water activity
(studied in water-ethanol mixtures) favoring the cyclic forms [83]. The function of a
transglycosylation reaction could be illustrated with using pure maltose as the
substrate for the enzyme CGTase. A decreasing concentration series of higher
polymerization degree malto-oligomers up to maltoheptaose was obtained. The
amount of glucose increased when the polymerization degrees increased. That is,
in a microbial medium, glucose could be ingested by the microbe producing the
enzyme, and CDs can serve as a prolonged supply of glucose. The reaction micromilieu also affects the results. Novel types of sugar syrups containing CDs were
obtained by adding immobilized CGTase enzyme to sugar syrup solutions. If free
soluble enzyme was added, the reaction was negligible [81, 82]. Glycosyltransferases
(exemplified here by the CGTase) can dynamically modify sugar polymers to get
specific and extremely complex EPSs. These carbohydrates can serve as nutrient
storages, means to cell protection, and adhesion to surfaces. The strategic advantage
is in the microbe’s individual structure of EPSs. The structures of different microbes
can originate from only slightly different compositions of enzymes and/or their
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
177
[78]. Without the property to the firm attachment, a microbe cannot be pathogenic,
as known from pathogenic and nonpathogenic E. coli strains. EPSs could provide an
evident survival mechanism to extremophiles for making capsules around the cells
and for binding to surfaces for propagation. Structures of EPSs vary and constitute a
wide spectrum of properties.
EPSs biosynthesis can take place either fully extracellularly or partly intracellularly and partly extracellularly. Glycosyltransferase enzymes make the complicated
transfers of sugar units in the growing polymer system. EPSs and their structures,
analysis, biosynthesis, and properties from extremophiles are reviewed in detail
[79]. Alkaliphiles have unusual structures of EPSs. Many haloalkaliphiles strains
produce more than one different EPS [79]. Natural or chemically functionalized
carbohydrates are important biotechnological products in industry as gelling agents,
thickeners, or edible films. EPSs also have multifarious biotechnological applications in food and pharmaceutical industries. Microbial EPSs could add to the
spectrum of related gum-like substances of non-microbial origin. Food industry is
strictly limited to certain accepted nonpathogenic producer strains. This limitation
does not apply to other technical applications where the product repertoire may thus
be much bigger.
Cyclodextrins (CDs) are ring-shaped glucose oligomers (6, 7, or 8 glucose units)
derived from starch by the enzyme cyclomaltodextrin glucanotransferase, CGTase
([80]; a review). Formally, CGTases are messengers of the cells, like any enzymes or
EPSs aimed at acquiring better living conditions for a microbe. There was for a long
time conception that there are separate enzymes for the different CD rings. It was
convincingly shown that there is only one enzyme by purifying CGTase from an
alkaliphilic Bacillus to an extremely homogenous stage on the immobiline
electrofocusing. There were microheterogenic fractions (one or two charge differences), but the CD profile was the same [81, 82]. However, the reaction conditions
affect the equilibrium between acyclic and cyclic forms of CDs, a low water activity
(studied in water-ethanol mixtures) favoring the cyclic forms [83]. The function of a
transglycosylation reaction could be illustrated with using pure maltose as the
substrate for the enzyme CGTase. A decreasing concentration series of higher
polymerization degree malto-oligomers up to maltoheptaose was obtained. The
amount of glucose increased when the polymerization degrees increased. That is,
in a microbial medium, glucose could be ingested by the microbe producing the
enzyme, and CDs can serve as a prolonged supply of glucose. The reaction micromilieu also affects the results. Novel types of sugar syrups containing CDs were
obtained by adding immobilized CGTase enzyme to sugar syrup solutions. If free
soluble enzyme was added, the reaction was negligible [81, 82]. Glycosyltransferases
(exemplified here by the CGTase) can dynamically modify sugar polymers to get
specific and extremely complex EPSs. These carbohydrates can serve as nutrient
storages, means to cell protection, and adhesion to surfaces. The strategic advantage
is in the microbe’s individual structure of EPSs. The structures of different microbes
can originate from only slightly different compositions of enzymes and/or their
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
177