thiosulfatophilus [71, 72]. Accumulation of demethylspheroidene and demethylspheroidenone carotenoids in substantial amounts was observed in the cells of a
novel alkaliphilic purple nonsulfur bacterium Rhodobaca bogoriensis strain LBB1.
That is regarded to be unique among anoxygenic phototrophs, as these two carotenoids are known intermediates of the spheroidene pathway, but their content is
typically low in organisms that express enzymes of this pathway [75]. A novel type
of membrane-bound yellow pigments was detected in the extremely salt-tolerant
alkaline strain of Thioalkalivibrio, whose specific concentration correlated with
increasing salinity of the growth medium. In contrast to carotenoids, the new
pigments possess considerably less carbon atoms (i.e., total number of carbon
atoms is 23) and have a straight polyene instead of an isoprenoid chain. This polyene
chain is terminated with a hydrophilic methylated phenol and a carboxymethyl
group. The compound (2) differs from the compound (1) by the presence of chloride
in the phenol group, which makes it even more unusual. The names natronochrome
and chloronatronochrome were suggested to the compounds (1) and (2) in Fig. 3,
respectively [76].
Marine alkali-tolerant strain 11shimoA1 (JCM19538), Jejuia pallidilutea, synthesized a novel monocyclic carotenoid, 2
0 -isopentenylsaproxanthin, as well as
zeaxanthin. Saproxanthin and myxol, which have monocyclic carotenoids with a
γ-carotene skeleton, have been reported to show a stronger antioxidant activity than
those with β-carotene and zeaxanthin. The strain 11shimoA1 produced more
2
0 -isopentenylsaproxanthin in the alkaline medium (pH 9.2) than in medium with
a pH of 7.0. These carotenoids are likely to play some roles in the adaptation of the
bacterium to the environmental conditions [77].
8 Exopolysaccharides
Microorganisms synthetize a wide spectrum of multifunctional polysaccharides
including intracellular, cell wall, and extracellular polysaccharides. Extracellular
polysaccharides, exopolysaccharides, or EPSs can be found in capsular materials
or as a dispersed slime with no obvious association to any one particular cell
common to the microbes. EPSs are composed of sugar monomers and some
noncarbohydrate substituents. Attachment to material surfaces (biofilms) is one
function of EPSs. EPSs could serve also as protective barrier to hostile environment
and an external energy storage for microbes.
Microbial sugar polymers and their derivatives form a very complicated and less
known class of chemical compounds. The statistical variability of the chemical
bonds can be enormous. There are analytical methods to study EPSs, but they are
laborious and demand specialists even though a great progress has taken place
during recent years for introducing advanced mass spectrometric and NMR methods.
Pathogenic microbes require first to make a firm adherence to host organs in order to
colonize. Pathogens have not only carbohydrates to attach but also protein chains
which are synthetized as monomers and joined together with “lock strands”
176
E. Khalikova et al.
novel alkaliphilic purple nonsulfur bacterium Rhodobaca bogoriensis strain LBB1.
That is regarded to be unique among anoxygenic phototrophs, as these two carotenoids are known intermediates of the spheroidene pathway, but their content is
typically low in organisms that express enzymes of this pathway [75]. A novel type
of membrane-bound yellow pigments was detected in the extremely salt-tolerant
alkaline strain of Thioalkalivibrio, whose specific concentration correlated with
increasing salinity of the growth medium. In contrast to carotenoids, the new
pigments possess considerably less carbon atoms (i.e., total number of carbon
atoms is 23) and have a straight polyene instead of an isoprenoid chain. This polyene
chain is terminated with a hydrophilic methylated phenol and a carboxymethyl
group. The compound (2) differs from the compound (1) by the presence of chloride
in the phenol group, which makes it even more unusual. The names natronochrome
and chloronatronochrome were suggested to the compounds (1) and (2) in Fig. 3,
respectively [76].
Marine alkali-tolerant strain 11shimoA1 (JCM19538), Jejuia pallidilutea, synthesized a novel monocyclic carotenoid, 2
0 -isopentenylsaproxanthin, as well as
zeaxanthin. Saproxanthin and myxol, which have monocyclic carotenoids with a
γ-carotene skeleton, have been reported to show a stronger antioxidant activity than
those with β-carotene and zeaxanthin. The strain 11shimoA1 produced more
2
0 -isopentenylsaproxanthin in the alkaline medium (pH 9.2) than in medium with
a pH of 7.0. These carotenoids are likely to play some roles in the adaptation of the
bacterium to the environmental conditions [77].
8 Exopolysaccharides
Microorganisms synthetize a wide spectrum of multifunctional polysaccharides
including intracellular, cell wall, and extracellular polysaccharides. Extracellular
polysaccharides, exopolysaccharides, or EPSs can be found in capsular materials
or as a dispersed slime with no obvious association to any one particular cell
common to the microbes. EPSs are composed of sugar monomers and some
noncarbohydrate substituents. Attachment to material surfaces (biofilms) is one
function of EPSs. EPSs could serve also as protective barrier to hostile environment
and an external energy storage for microbes.
Microbial sugar polymers and their derivatives form a very complicated and less
known class of chemical compounds. The statistical variability of the chemical
bonds can be enormous. There are analytical methods to study EPSs, but they are
laborious and demand specialists even though a great progress has taken place
during recent years for introducing advanced mass spectrometric and NMR methods.
Pathogenic microbes require first to make a firm adherence to host organs in order to
colonize. Pathogens have not only carbohydrates to attach but also protein chains
which are synthetized as monomers and joined together with “lock strands”
176
E. Khalikova et al.