using [276]. Similarly, the degradation of azo dyes and nitroaromatics by NDP(H)dependent azoreductase from an alkaliphilic strain Aquiflexum sp. DL6 is
reported [277].
Petroleum industries and oil refineries often contaminate aquatic and terrestrial
environments with a range of hydrocarbons. Removal of these pollutants has always
been important, and it seems that alkaliphiles have a great potential in remediation of
environments polluted with hydrocarbons and its derivatives. An array of
alkaliphiles belonging to the genera Dietzia, Micrococcus, Bacillus, Oceanobacillus,
Citricoccus, Cronobacter, Marinobacter, Psychralcaliphila, Halomonas,
Alteromonas, etc. are capable of efficiently degrading and metabolizing these pollutants [194, 278–282]. Moreover, benzoates and pyrenes which are widely used in
several industries and appear in many environments as pollutants can be degraded
and removed by alkaliphilic microbes such as Bacillus krulwichiae, Mycobacterium
sp., Halomonas campisalis, and Bacillus badius [283–285], a phenomenon which
indicates the alkaliphiles’ bioremediation potential.
Activities such as jewelry-making, gold mining, steel and aluminum processing,
electroplating, and production of nitrile pesticides generate highly toxic cyanidecontaining wastewater which need to be treated. Although cyanides are known to be
highly toxic and lethal, a handful of organisms are known to resist this effect. One of
such organisms is the alkaliphilic strain of Pseudomonas pseudoalcaligenes which
utilizes cyanide as sole nitrogen source and has been used effectively to treat
wastewater containing cyanide [286, 287].
Heavy metal pollution is a serious concern not only due to its toxicity but also due
to its recalcitrant nature. Unlike organic pollutants, heavy metals are not biodegradable, and removing these contaminants from polluted environments has been a
challenge. Microbes which are capable of precipitating metal ions are very attractive
in handling heavy metal pollution. In this regard, alkaliphiles which are known for
their effective siderophores, organic acids, and innate abilities of reducing metals can
be of great importance. For example, the alkaliphilic bacteria Alkaliphilus
metalliredigens QYMF cells are known to effectively reduce iron in anaerobic
alkaline condition and precipitate it [260, 261]; this shows the possibility of using
such alkaliphiles in removing metal contaminants from alkaline effluents. The
alkaliphile-induced metal precipitation is expected to reduce the metal mobility
which subsequently prevents the spreading of the pollutant.
Another area where alkaliphiles are useful in managing waste is in the textile and
leather industry. The roles of alkaliphiles in the leather industry are discussed in this
volume(see [288]) and hence, will not be discussed here. In the textile industry,
bleaching is performed using alkaline hydrogen peroxide which is accompanied by
washing. However, if the copious amount of water used in the extensive washing of
the bleaching agent must be recycled, the hydrogen peroxide should be removed. In
this regard, the use of alkaline active catalases or alkaliphiles is the most attractive
approach which provides economic, environmental, and technical rewards [289–
292].
As a way of counteracting the high pH effect of their habitats, alkaliphiles often
produce organic acids. This ability of alkaliphiles can be tapped to neutralize
Alkaliphiles: The Versatile Tools in Biotechnology
35
reported [277].
Petroleum industries and oil refineries often contaminate aquatic and terrestrial
environments with a range of hydrocarbons. Removal of these pollutants has always
been important, and it seems that alkaliphiles have a great potential in remediation of
environments polluted with hydrocarbons and its derivatives. An array of
alkaliphiles belonging to the genera Dietzia, Micrococcus, Bacillus, Oceanobacillus,
Citricoccus, Cronobacter, Marinobacter, Psychralcaliphila, Halomonas,
Alteromonas, etc. are capable of efficiently degrading and metabolizing these pollutants [194, 278–282]. Moreover, benzoates and pyrenes which are widely used in
several industries and appear in many environments as pollutants can be degraded
and removed by alkaliphilic microbes such as Bacillus krulwichiae, Mycobacterium
sp., Halomonas campisalis, and Bacillus badius [283–285], a phenomenon which
indicates the alkaliphiles’ bioremediation potential.
Activities such as jewelry-making, gold mining, steel and aluminum processing,
electroplating, and production of nitrile pesticides generate highly toxic cyanidecontaining wastewater which need to be treated. Although cyanides are known to be
highly toxic and lethal, a handful of organisms are known to resist this effect. One of
such organisms is the alkaliphilic strain of Pseudomonas pseudoalcaligenes which
utilizes cyanide as sole nitrogen source and has been used effectively to treat
wastewater containing cyanide [286, 287].
Heavy metal pollution is a serious concern not only due to its toxicity but also due
to its recalcitrant nature. Unlike organic pollutants, heavy metals are not biodegradable, and removing these contaminants from polluted environments has been a
challenge. Microbes which are capable of precipitating metal ions are very attractive
in handling heavy metal pollution. In this regard, alkaliphiles which are known for
their effective siderophores, organic acids, and innate abilities of reducing metals can
be of great importance. For example, the alkaliphilic bacteria Alkaliphilus
metalliredigens QYMF cells are known to effectively reduce iron in anaerobic
alkaline condition and precipitate it [260, 261]; this shows the possibility of using
such alkaliphiles in removing metal contaminants from alkaline effluents. The
alkaliphile-induced metal precipitation is expected to reduce the metal mobility
which subsequently prevents the spreading of the pollutant.
Another area where alkaliphiles are useful in managing waste is in the textile and
leather industry. The roles of alkaliphiles in the leather industry are discussed in this
volume(see [288]) and hence, will not be discussed here. In the textile industry,
bleaching is performed using alkaline hydrogen peroxide which is accompanied by
washing. However, if the copious amount of water used in the extensive washing of
the bleaching agent must be recycled, the hydrogen peroxide should be removed. In
this regard, the use of alkaline active catalases or alkaliphiles is the most attractive
approach which provides economic, environmental, and technical rewards [289–
292].
As a way of counteracting the high pH effect of their habitats, alkaliphiles often
produce organic acids. This ability of alkaliphiles can be tapped to neutralize
Alkaliphiles: The Versatile Tools in Biotechnology
35