An alkaliphilic bacterium, Alkaliphilus metalliredigens, was isolated from leachate ponds at the US Borax Company, Boron, California. It was able to grow with
metals Fe(III)-citrate, Fe(III)-EDTA, Co(III)-EDTA, and Cr(VI) as the electron
acceptors, at pH values up to 11 in the presence of elevated salt levels in anaerobic
conditions. This metal-reducing bacterium might be unique for bioremediation of
metal-contaminated alkaline environments and for mobilizing metal ions in the
process of bioleaching in anaerobic conditions [52]. An alkaliphilic bacterial isolate
Halomonas sp. SL01 was found to produce relatively high concentrations of
siderophores in liquid medium (up to 40 μM). Structure of the purified siderophore
was determined using LC/MS and fatty acid methyl ester (FAME) GC. Two distinct
new families of amphiphilic siderophores were produced by the isolate SL01. All the
siderophores were 989–1,096 Da in size and consisted of a conserved peptide-head
group, which binds iron together with coordinated fatty acids. These siderophores
resembled amphiphilic aquachelin siderophores produced by H. aquamarina strain
DS40M3, a marine bacterium, as well as siderophores from Halomonas sp. SL28
which also produced amphiphilic siderophores. The names of halochelins B, C, D, E,
and F were proposed for the siderophores produced by Halomonas sp. SL01 [53].
The alkaliphilic strain Pseudomonas pseudoalcaligenes CECT5344 isolated from
sludge of the Guadalquivir River (Cordoba, Spain) can metabolize cyanide, cyanate,
some metal-cyanide complexes, and different nitriles (cyanohydrins) as nitrogen
source under alkaline conditions, thus preventing volatile HCN formation. This
strain was able to tolerate pH of 11.5 and up to 100 mM cyanate. Although it
has been discussed that the synthesis of siderophores for iron acquisition should
be necessary for an efficient cyanide assimilation process, it seems that
Pseudoalcaligenes CECT5344 does not produce siderophores and lacks putative
genes involved in the synthesis of these ferric ion-specific chelators [54]. However,
quantitative proteomic analysis revealed that the cyanotrophic strain possesses the
ferric-uptake system FhuC (ATP-binding component of a hydroxamate-type
siderophore import system) [55]. It can use Prussian blue as the source of nitrogen
and iron generating decolored halos around the colonies when growing on agar
plates [54].
Two siderophore-producing strains VITVK5 and VITVK6 were found and characterized [56]. The bacterial isolates showed a close resemblance to species of the
genera Bacillus and Enterobacter sp., respectively. Both strains grew and produced
siderophores in the pH range of 4.0–10 and temperature 25–45
C and optimally
produce siderophores at pH 8 and at 37
C with glucose or sucrose as the carbon
source and NaNO 3 as the nitrogen source. The strains VITVK5 and VITVK6 are
promising candidates for the production of the siderophores because of simple
nutrient requirement. The authors considered them to suit for many applications in
medicine and industry [56].
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
173
metals Fe(III)-citrate, Fe(III)-EDTA, Co(III)-EDTA, and Cr(VI) as the electron
acceptors, at pH values up to 11 in the presence of elevated salt levels in anaerobic
conditions. This metal-reducing bacterium might be unique for bioremediation of
metal-contaminated alkaline environments and for mobilizing metal ions in the
process of bioleaching in anaerobic conditions [52]. An alkaliphilic bacterial isolate
Halomonas sp. SL01 was found to produce relatively high concentrations of
siderophores in liquid medium (up to 40 μM). Structure of the purified siderophore
was determined using LC/MS and fatty acid methyl ester (FAME) GC. Two distinct
new families of amphiphilic siderophores were produced by the isolate SL01. All the
siderophores were 989–1,096 Da in size and consisted of a conserved peptide-head
group, which binds iron together with coordinated fatty acids. These siderophores
resembled amphiphilic aquachelin siderophores produced by H. aquamarina strain
DS40M3, a marine bacterium, as well as siderophores from Halomonas sp. SL28
which also produced amphiphilic siderophores. The names of halochelins B, C, D, E,
and F were proposed for the siderophores produced by Halomonas sp. SL01 [53].
The alkaliphilic strain Pseudomonas pseudoalcaligenes CECT5344 isolated from
sludge of the Guadalquivir River (Cordoba, Spain) can metabolize cyanide, cyanate,
some metal-cyanide complexes, and different nitriles (cyanohydrins) as nitrogen
source under alkaline conditions, thus preventing volatile HCN formation. This
strain was able to tolerate pH of 11.5 and up to 100 mM cyanate. Although it
has been discussed that the synthesis of siderophores for iron acquisition should
be necessary for an efficient cyanide assimilation process, it seems that
Pseudoalcaligenes CECT5344 does not produce siderophores and lacks putative
genes involved in the synthesis of these ferric ion-specific chelators [54]. However,
quantitative proteomic analysis revealed that the cyanotrophic strain possesses the
ferric-uptake system FhuC (ATP-binding component of a hydroxamate-type
siderophore import system) [55]. It can use Prussian blue as the source of nitrogen
and iron generating decolored halos around the colonies when growing on agar
plates [54].
Two siderophore-producing strains VITVK5 and VITVK6 were found and characterized [56]. The bacterial isolates showed a close resemblance to species of the
genera Bacillus and Enterobacter sp., respectively. Both strains grew and produced
siderophores in the pH range of 4.0–10 and temperature 25–45
C and optimally
produce siderophores at pH 8 and at 37
C with glucose or sucrose as the carbon
source and NaNO 3 as the nitrogen source. The strains VITVK5 and VITVK6 are
promising candidates for the production of the siderophores because of simple
nutrient requirement. The authors considered them to suit for many applications in
medicine and industry [56].
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
173