lipopeptide nature of the surfactant [30]. Biosurfactant production by marine
alkaliphilic bacterium Pseudomonas aeruginosa was strongly dependent on the
cultivation pH. The strain was able to grow and reduce the surface tension of the
culture broth to 28 mN/m when cultured using sunflower oil as the sole carbon
source and peptone as the nitrogen source in pH 9 medium and at 30
C [36].
Ochrobactrum intermedium produces a thermostable lipase and biosurfactants
and known to be resistant to alkaline washing powders. Biosurfactant produced by
O. intermedium exhibited high stability at pH 10–13 and temperature of 70–90
C.
The biosurfactant was stable in the presence of various metal ions, detergents, and
organic solvents and exhibited good antimicrobial activity [35]. The biosurfactants
produced by the marine bacteria Bacillus amyloliquefaciens and Bacillus
thuringiensis showed high emulsifying indexes. These biosurfactants were stable
at moderate temperature (30
C), high alkalinity (pH 11), and high salt concentration
(15%, w/v). Characterization of a partially purified biosurfactant from the most
active strain, B. amyloliquefaciens, indicated that the biosurfactant is a non-anionic
didemnin surfactant [29].
The lipopeptide biosurfactant produced by a strain of Hydrogenophaga sp. under
iron-reducing condition facilitated anaerobic degradation of pyrene and benzopyrene. Temperature and initial pH value of medium for both aerobic and anaerobic
growth were set at 28
C and pH 9.0, respectively. This indigenous alkaliphilic
organism seems to be suitable for bioremediation of petroleum- contaminated
alkaline sediment [37].
6 Siderophores
Iron (Fe) in its different ionic forms is biologically active compound which have
various functions in living organisms. Two readily convertible ferrous Fe(II) and
ferric Fe(III) forms allow iron to play pivotal role in numerous electron transfer
processes. The precisely tuned steric and electronic environments within enzyme
active sites permit even more highly oxidized Fe(IV) and Fe(V) or reduced Fe(I)
states to function as intermediates of enzyme catalyzes. Iron ions have been studied
for decades in bioorganic chemistry, and their coordination chemistry has solid
background as can be found in textbooks. Iron is an essential nutrient for all
known life forms.
Under iron-depleted conditions, microorganisms secrete small molecules known
as siderophores (Greek: “iron carrier”). These compounds have high affinity for iron
and are known to be iron-chelating agents. Siderophores may serve as iron transporters through the cell membrane of microbes. This is the traditional function, but
studies have shown that the role of siderophores is far more complex. At present,
nearly 500 structures of siderophores are reported from various microorganisms
[41]. The paper by Johnstone and Nolan [42] also reviews structural families of
siderophores. Typical metal-binding motifs of siderophores are catecholates,
hydroxamates, and alpha-hydroxycarboxylic acids. In addition to iron ions, many
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
171
alkaliphilic bacterium Pseudomonas aeruginosa was strongly dependent on the
cultivation pH. The strain was able to grow and reduce the surface tension of the
culture broth to 28 mN/m when cultured using sunflower oil as the sole carbon
source and peptone as the nitrogen source in pH 9 medium and at 30
C [36].
Ochrobactrum intermedium produces a thermostable lipase and biosurfactants
and known to be resistant to alkaline washing powders. Biosurfactant produced by
O. intermedium exhibited high stability at pH 10–13 and temperature of 70–90
C.
The biosurfactant was stable in the presence of various metal ions, detergents, and
organic solvents and exhibited good antimicrobial activity [35]. The biosurfactants
produced by the marine bacteria Bacillus amyloliquefaciens and Bacillus
thuringiensis showed high emulsifying indexes. These biosurfactants were stable
at moderate temperature (30
C), high alkalinity (pH 11), and high salt concentration
(15%, w/v). Characterization of a partially purified biosurfactant from the most
active strain, B. amyloliquefaciens, indicated that the biosurfactant is a non-anionic
didemnin surfactant [29].
The lipopeptide biosurfactant produced by a strain of Hydrogenophaga sp. under
iron-reducing condition facilitated anaerobic degradation of pyrene and benzopyrene. Temperature and initial pH value of medium for both aerobic and anaerobic
growth were set at 28
C and pH 9.0, respectively. This indigenous alkaliphilic
organism seems to be suitable for bioremediation of petroleum- contaminated
alkaline sediment [37].
6 Siderophores
Iron (Fe) in its different ionic forms is biologically active compound which have
various functions in living organisms. Two readily convertible ferrous Fe(II) and
ferric Fe(III) forms allow iron to play pivotal role in numerous electron transfer
processes. The precisely tuned steric and electronic environments within enzyme
active sites permit even more highly oxidized Fe(IV) and Fe(V) or reduced Fe(I)
states to function as intermediates of enzyme catalyzes. Iron ions have been studied
for decades in bioorganic chemistry, and their coordination chemistry has solid
background as can be found in textbooks. Iron is an essential nutrient for all
known life forms.
Under iron-depleted conditions, microorganisms secrete small molecules known
as siderophores (Greek: “iron carrier”). These compounds have high affinity for iron
and are known to be iron-chelating agents. Siderophores may serve as iron transporters through the cell membrane of microbes. This is the traditional function, but
studies have shown that the role of siderophores is far more complex. At present,
nearly 500 structures of siderophores are reported from various microorganisms
[41]. The paper by Johnstone and Nolan [42] also reviews structural families of
siderophores. Typical metal-binding motifs of siderophores are catecholates,
hydroxamates, and alpha-hydroxycarboxylic acids. In addition to iron ions, many
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
171