environments. Below is an account of the usefulness of each group as bioremediation agents.
Bacterial Remediation
Bacteria possess multiple bioremediation potentials and hence certainly are beneficial agents, from both environmental and economic point of view, for toxic pollutants cleanup. Such bioremediation (of toxic pollutants including metals/metalloids)
is achieved by using native bacteria isolated from the contaminated sites and
stimulating their detoxification ability by process and product engineering (Das
and Dash 2014). The use of suitable non-native and/or genetically engineered
microbes suited for arsenic bioremediation has been successfully demonstrated at
least at research-scale if not at field-scale (Das and Dash 2014).
Mechanism of Arsenic Bioremediation
The mechanisms in arsenic bioremediation are majorly biotransformation and
biosorption.
Biotransformation Mechanism
In this, the microbes could decrease the toxicity of the contaminants by using them
as energy sources while transforming them through the energy-yielding oxidationreduction reactions utilising oxygen, carbon dioxide, nitrates, sulphate acetate,
lactate and glucose as electron acceptors/donors during metabolism (Dey et al.
2017; Akhtar et al. 2013). Dey et al. (2017) reported that the bacteria having the
capacity to resist toxic metals can chemically transform heavy metals/metalloids
through their common cellular metabolism through oxidation, reduction, methylation, demethylation, precipitation etc. Bacteria could exploit arsenic in their metabolic process either as an electron acceptor as in case of anaerobic respiration or as an
electron donor as in case of chemoautotrophic fixation of CO 2 into cell carbon
(Akhtar et al. 2013). Dissimilatory arsenate-reducing bacteria use arsenate as an
electron acceptor and reduce it to arsenite. Chemoautotrophic arsenite oxidising
bacteria use CO 2 as the carbon source and arsenite as an electron acceptor, oxidising
it to arsenate for energy, whereas heterotrophic arsenite oxidisers use oxygen as an
electron acceptor to oxidise arsenite to arsenate (Fig. 8.3; Akhtar et al. 2013).
Biosorption of Arsenic
Microbial arsenic biosorption involves the sorption of arsenate ions (sorbate) present
in aqueous form on to the surface of a solid microbial biomass (biosorbent). Due to
their higher affinity towards charged ions which further dependent on the chemical
constituents of the cell wall, biosorbents facilitate the binding of the contaminant
ions. Further, the degree of biosorption differs according to the distribution of
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P. K. Parhi et al.
Bacterial Remediation
Bacteria possess multiple bioremediation potentials and hence certainly are beneficial agents, from both environmental and economic point of view, for toxic pollutants cleanup. Such bioremediation (of toxic pollutants including metals/metalloids)
is achieved by using native bacteria isolated from the contaminated sites and
stimulating their detoxification ability by process and product engineering (Das
and Dash 2014). The use of suitable non-native and/or genetically engineered
microbes suited for arsenic bioremediation has been successfully demonstrated at
least at research-scale if not at field-scale (Das and Dash 2014).
Mechanism of Arsenic Bioremediation
The mechanisms in arsenic bioremediation are majorly biotransformation and
biosorption.
Biotransformation Mechanism
In this, the microbes could decrease the toxicity of the contaminants by using them
as energy sources while transforming them through the energy-yielding oxidationreduction reactions utilising oxygen, carbon dioxide, nitrates, sulphate acetate,
lactate and glucose as electron acceptors/donors during metabolism (Dey et al.
2017; Akhtar et al. 2013). Dey et al. (2017) reported that the bacteria having the
capacity to resist toxic metals can chemically transform heavy metals/metalloids
through their common cellular metabolism through oxidation, reduction, methylation, demethylation, precipitation etc. Bacteria could exploit arsenic in their metabolic process either as an electron acceptor as in case of anaerobic respiration or as an
electron donor as in case of chemoautotrophic fixation of CO 2 into cell carbon
(Akhtar et al. 2013). Dissimilatory arsenate-reducing bacteria use arsenate as an
electron acceptor and reduce it to arsenite. Chemoautotrophic arsenite oxidising
bacteria use CO 2 as the carbon source and arsenite as an electron acceptor, oxidising
it to arsenate for energy, whereas heterotrophic arsenite oxidisers use oxygen as an
electron acceptor to oxidise arsenite to arsenate (Fig. 8.3; Akhtar et al. 2013).
Biosorption of Arsenic
Microbial arsenic biosorption involves the sorption of arsenate ions (sorbate) present
in aqueous form on to the surface of a solid microbial biomass (biosorbent). Due to
their higher affinity towards charged ions which further dependent on the chemical
constituents of the cell wall, biosorbents facilitate the binding of the contaminant
ions. Further, the degree of biosorption differs according to the distribution of
228
P. K. Parhi et al.