be injected into the column. However, if the sulfide content is high, there will be a
precipitate that must be separated from the rest of the solution. For instance, this
should be done when analyzing organic products in the course of anaerobic respiration with sulfate or sulfur when sulfide content in the sample can reach 1 g/L and
even higher. In this case, after preliminary acidification, a small amount of 30%
H 2 O 2 is added. Precipitation of sulfur takes several hours (depending on the initial
sulfide content), and after its completion, a little dry MnO 2 is put into the reaction
mixture. The latter will decompose the unreacted H 2 O 2 , since in case of entering the
column, hydrogen peroxide can disrupt covalent linkages in the ion-exchange resin.
The reaction mixture must then be clarified by centrifugation or filtration, and the
sample can be safely injected. Since hydrogen peroxide is a strong oxidizer, drawback of the method is the possible oxidation of unstable substrates/products, if they
are present in the sample. If it is known a priori, another technique involving the use
of heavy metal salts (Cu
2+ , Sn
2+ ) can be applied. These cations bind the soluble
sulfide and precipitate it in an insoluble form stable at acidic conditions. The reaction
proceeds quickly, but this technique should be applied with caution, if used in excess
the free metal ions in the reaction mixture can bind to the resin too and, subsequently, are difficult to wash off the column. Thiosulfate (often used as an electron
acceptor) is also unstable in the acidic eluent and, if present, is degraded to sulfur.
So, the abovementioned notes about sulfide removal are also valid for this sulfur
species.
Another risk associated with the analysis of brines is the possibility of salt
precipitation (the salting out effect) if the eluent contains some organic modifier
(e.g., methanol or acetonitrile) that may result in clogging of the capillaries.
To avoid, in advance, it is necessary to mix the test sample with the eluent in various
proportions, in order to make sure that there is no salting out.
6 Concluding Remarks
The increasing number of publications on alkaliphilic microorganisms convincingly
demonstrates their importance for both fundamental and applied research in microbiology and biotechnology. It is now generally accepted that alkaliphiles, along with
thermophiles, are the oldest organisms on Earth, and their study from the standpoint
of paleomicrobiology will provide more knowledge about Earth’s history when the
biosphere was exclusively prokaryotic. This knowledge can be especially valuable in
the case of discovery of extraterrestrial life. At the same time, despite the large
number of already known alkaliphiles and the commonness of the basic biochemical
processes, nature gives practically “inexhaustible” combinations of biomolecules,
including industrially important enzymes. Therefore, the search for this group of
microorganisms will continue to isolate alkaliphiles which are still waiting for their
discoverers.
76
V. V. Kevbrin
precipitate that must be separated from the rest of the solution. For instance, this
should be done when analyzing organic products in the course of anaerobic respiration with sulfate or sulfur when sulfide content in the sample can reach 1 g/L and
even higher. In this case, after preliminary acidification, a small amount of 30%
H 2 O 2 is added. Precipitation of sulfur takes several hours (depending on the initial
sulfide content), and after its completion, a little dry MnO 2 is put into the reaction
mixture. The latter will decompose the unreacted H 2 O 2 , since in case of entering the
column, hydrogen peroxide can disrupt covalent linkages in the ion-exchange resin.
The reaction mixture must then be clarified by centrifugation or filtration, and the
sample can be safely injected. Since hydrogen peroxide is a strong oxidizer, drawback of the method is the possible oxidation of unstable substrates/products, if they
are present in the sample. If it is known a priori, another technique involving the use
of heavy metal salts (Cu
2+ , Sn
2+ ) can be applied. These cations bind the soluble
sulfide and precipitate it in an insoluble form stable at acidic conditions. The reaction
proceeds quickly, but this technique should be applied with caution, if used in excess
the free metal ions in the reaction mixture can bind to the resin too and, subsequently, are difficult to wash off the column. Thiosulfate (often used as an electron
acceptor) is also unstable in the acidic eluent and, if present, is degraded to sulfur.
So, the abovementioned notes about sulfide removal are also valid for this sulfur
species.
Another risk associated with the analysis of brines is the possibility of salt
precipitation (the salting out effect) if the eluent contains some organic modifier
(e.g., methanol or acetonitrile) that may result in clogging of the capillaries.
To avoid, in advance, it is necessary to mix the test sample with the eluent in various
proportions, in order to make sure that there is no salting out.
6 Concluding Remarks
The increasing number of publications on alkaliphilic microorganisms convincingly
demonstrates their importance for both fundamental and applied research in microbiology and biotechnology. It is now generally accepted that alkaliphiles, along with
thermophiles, are the oldest organisms on Earth, and their study from the standpoint
of paleomicrobiology will provide more knowledge about Earth’s history when the
biosphere was exclusively prokaryotic. This knowledge can be especially valuable in
the case of discovery of extraterrestrial life. At the same time, despite the large
number of already known alkaliphiles and the commonness of the basic biochemical
processes, nature gives practically “inexhaustible” combinations of biomolecules,
including industrially important enzymes. Therefore, the search for this group of
microorganisms will continue to isolate alkaliphiles which are still waiting for their
discoverers.
76
V. V. Kevbrin