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A. Das et al.
1 Introduction
Arsenic is a metalloid element which is widely distributed on surface of the earth.
Arsenic is 20th most abundant element in earth’s crust, 14th in seawater and 12th in
human body (Woolson 1975). Arsenic is a highly toxic pollutant that is released in
the environment due to the natural calamities and anthropogenic actions. The indiscriminate release of the heavy metal into the soil and water is a major health concern
worldwide, as it cannot be broken down into non-toxic form and therefore has longlasting effects on ecosystem (Dixit et al. 2015). Arsenic is found in almost 20 minerals
but the free metal is rare. The major forms of arsenic in environment exist in several
oxidation states, As(V), As(III), As(0), and Arsenide(-III). The most common forms
encountered in the soil are As(V) and As(III); i.e. arsenate and arsenite. Arsenite is
the most toxic form of arsenic salt. Arsenic is exposed in the environment through the
pedogenic process of weathering and also through human activities. The most significant natural source is weathering of minerals, erosion and volcanic activities (Dixit
et al. 2015). The anthropogenic activities which release arsenic in the environment are
mining, industries, agrochemicals, waste disposal and atmospheric disposal. Toxicity
of Arsenic varies amongst the nature of species as well as with the oxidation state of
the metal ion (Acharya et al. 1999). The probable reason has been explained as the
expression of genes which are involved in the synthesis of AQP9 enzymes (Acharya
et al. 1999). The toxicity of the arsenite is due to its affinity for closely-related spaced
cysteine thiolates, it inactivates enzymes and receptors by binding to active site of
cysteine residue, formation of disulphide bonds and production of reactive oxygen
species by binding to reduced glutathione (Bhattacharjee et al. 2008). The industries such as paint, mining, agrochemicals are the major source of arsenic pollution.
The groundwater is contaminated heavily due to effluents released by these industries. This has been recognized as one of the major catastrophic proportions. One
doesn’t normally associate arsenic with life, but it is now apparent that various types
of microorganisms gain energy for growth from these toxic metals (Oremland and
Stolz 2005). Microorganisms and their enzymes are actively involved in the arsenic
cycle. They are involved in oxidation, reduction and methylation reactions. Usually,
microbes have two types of uptake system, one is non-specific and the other is highly
substrate specific. Bioremediation is the microbial-based cleaning mechanism of
contaminants which may include toxins like hydrocarbons, agrochemicals and other
organic toxicants. The heavy metals are not entirely rendered harmless by microbes
and their enzymes but this is the technology they use to get rid of the arsenic. Potent
metal sorbent bacteria are under the genera of Bacillus, Pseudomonads, Streptomyces
and P. Aeroginosa. The mechanism that involves tolerating the metal in their cell has
been reported as, (i) Exclusion of the metal ions by keeping away from the target sites;
(ii) extrusion of the metals by pushing out of the cell through chromosomal/plasmidmediated events; (iii) accommodation of metal form complex with the metal-binding
proteins or other cell components; (iv) biotransformation: toxic metal is reduced to
less toxic forms and (v) methylation and demethylation. This study aims to isolate,
A. Das et al.
1 Introduction
Arsenic is a metalloid element which is widely distributed on surface of the earth.
Arsenic is 20th most abundant element in earth’s crust, 14th in seawater and 12th in
human body (Woolson 1975). Arsenic is a highly toxic pollutant that is released in
the environment due to the natural calamities and anthropogenic actions. The indiscriminate release of the heavy metal into the soil and water is a major health concern
worldwide, as it cannot be broken down into non-toxic form and therefore has longlasting effects on ecosystem (Dixit et al. 2015). Arsenic is found in almost 20 minerals
but the free metal is rare. The major forms of arsenic in environment exist in several
oxidation states, As(V), As(III), As(0), and Arsenide(-III). The most common forms
encountered in the soil are As(V) and As(III); i.e. arsenate and arsenite. Arsenite is
the most toxic form of arsenic salt. Arsenic is exposed in the environment through the
pedogenic process of weathering and also through human activities. The most significant natural source is weathering of minerals, erosion and volcanic activities (Dixit
et al. 2015). The anthropogenic activities which release arsenic in the environment are
mining, industries, agrochemicals, waste disposal and atmospheric disposal. Toxicity
of Arsenic varies amongst the nature of species as well as with the oxidation state of
the metal ion (Acharya et al. 1999). The probable reason has been explained as the
expression of genes which are involved in the synthesis of AQP9 enzymes (Acharya
et al. 1999). The toxicity of the arsenite is due to its affinity for closely-related spaced
cysteine thiolates, it inactivates enzymes and receptors by binding to active site of
cysteine residue, formation of disulphide bonds and production of reactive oxygen
species by binding to reduced glutathione (Bhattacharjee et al. 2008). The industries such as paint, mining, agrochemicals are the major source of arsenic pollution.
The groundwater is contaminated heavily due to effluents released by these industries. This has been recognized as one of the major catastrophic proportions. One
doesn’t normally associate arsenic with life, but it is now apparent that various types
of microorganisms gain energy for growth from these toxic metals (Oremland and
Stolz 2005). Microorganisms and their enzymes are actively involved in the arsenic
cycle. They are involved in oxidation, reduction and methylation reactions. Usually,
microbes have two types of uptake system, one is non-specific and the other is highly
substrate specific. Bioremediation is the microbial-based cleaning mechanism of
contaminants which may include toxins like hydrocarbons, agrochemicals and other
organic toxicants. The heavy metals are not entirely rendered harmless by microbes
and their enzymes but this is the technology they use to get rid of the arsenic. Potent
metal sorbent bacteria are under the genera of Bacillus, Pseudomonads, Streptomyces
and P. Aeroginosa. The mechanism that involves tolerating the metal in their cell has
been reported as, (i) Exclusion of the metal ions by keeping away from the target sites;
(ii) extrusion of the metals by pushing out of the cell through chromosomal/plasmidmediated events; (iii) accommodation of metal form complex with the metal-binding
proteins or other cell components; (iv) biotransformation: toxic metal is reduced to
less toxic forms and (v) methylation and demethylation. This study aims to isolate,