proteins with hydroxyl, phosphate, sulphate and amino functional groups that could
bind to the metal ions and metalloids relatively easily (Maheswari and Murugesan
2011). Most fungi, viz., Trichoderma, Candida, Aspergillus, Fusarium and Penicillium, help in methylating inorganic arsenic to its organic counterpart (Upadhyay
et al. 2018). The advantages of fungi over bacteria as bioremediation agents are their
longer life-span, higher biomass content and a complex hyphal network (Singh et al.
2016). Additionally, metal savouring fungi can compete with native bacteria in
relatively inhospitable conditions (Sun et al. 2012).
Trichoderma is another filamentous Ascomycete fungus of great significance in
plant growth promotion (Waghunde et al. 2016). It improves soil fertility and has the
ability to induce stress-tolerance, a peculiar characteristic unlike the competing
neighbouring rhizospheric microbes. It could promote hormone production, nutrient
release from the soil, and rhizosphere development (de Souza et al. 2017). It contains
a variety of functional groups on the outer layer of cell wall that could bind to metal
ions and metalloids (Tripathi et al. 2017). Westerdykella aurantiaca, a soil fungus,
bears arsenic methyl-transferase (WaarsM) gene which could be expressed in Saccharomyces cerevisiae (Verma and Jaiswal 2016). Such bioengineered yeasts capable of expressing the WaarsM gene demonstrated a higher arsenic methylation
property. Laboratory studies confirmed an enhanced arsenic tolerance in paddy
when such yeast cells were cocultured/inoculated in paddy (Verma and Jaiswal
2016).
8.5 Approach Involving Plant-Microbe Associations
Phytoremediation is a selective way used by plants to clean heavy metals from the
environment through modified rhizospheric PGPR and PGPM. Several studies have
been performed to select hyper-accumulating plants to assess the consequence of
metal stress on the useful rhizospheric microbes (PGPMs) that can further facilitate
the development of a more promising bioremediation strategy (Tak et al. 2013). The
efficacy of phytoremediation is limited by the major factors, such as, tolerance level
for the contaminant by the plant, selection of the plant variety to be employed for
bioremediation, and its capacity to uptake and translocate the heavy metals (Jutsz
and Gnida 2015). Phytoremediation, as indicated earlier, is an economically feasible
bioremediation strategy as it produces the utilisable biomass while removing the
toxic metals (Angelova et al. 2016).
Most plant species harbour vesicular-arbuscular mycorrhizae (VAM) that primarily help in phosphate solubilisation and uptake thereby enhancing their stress
tolerance ability (Sharma et al. 2017). Upadhyay et al. (2018) reported that VAM
supplementation helped overcome arsenic-induced phosphate deficiency in wheat.
VAM also helps in maintaining a good ratio of arsenic and phosphate by
translocating arsenic to inside the plant cells, particularly in soils with low arsenic
contamination. In a similar study, Li et al. (2016) observed a decrease in the
8 Arsenic Contamination: Sources, Chemistry and Remediation Strategies
231
bind to the metal ions and metalloids relatively easily (Maheswari and Murugesan
2011). Most fungi, viz., Trichoderma, Candida, Aspergillus, Fusarium and Penicillium, help in methylating inorganic arsenic to its organic counterpart (Upadhyay
et al. 2018). The advantages of fungi over bacteria as bioremediation agents are their
longer life-span, higher biomass content and a complex hyphal network (Singh et al.
2016). Additionally, metal savouring fungi can compete with native bacteria in
relatively inhospitable conditions (Sun et al. 2012).
Trichoderma is another filamentous Ascomycete fungus of great significance in
plant growth promotion (Waghunde et al. 2016). It improves soil fertility and has the
ability to induce stress-tolerance, a peculiar characteristic unlike the competing
neighbouring rhizospheric microbes. It could promote hormone production, nutrient
release from the soil, and rhizosphere development (de Souza et al. 2017). It contains
a variety of functional groups on the outer layer of cell wall that could bind to metal
ions and metalloids (Tripathi et al. 2017). Westerdykella aurantiaca, a soil fungus,
bears arsenic methyl-transferase (WaarsM) gene which could be expressed in Saccharomyces cerevisiae (Verma and Jaiswal 2016). Such bioengineered yeasts capable of expressing the WaarsM gene demonstrated a higher arsenic methylation
property. Laboratory studies confirmed an enhanced arsenic tolerance in paddy
when such yeast cells were cocultured/inoculated in paddy (Verma and Jaiswal
2016).
8.5 Approach Involving Plant-Microbe Associations
Phytoremediation is a selective way used by plants to clean heavy metals from the
environment through modified rhizospheric PGPR and PGPM. Several studies have
been performed to select hyper-accumulating plants to assess the consequence of
metal stress on the useful rhizospheric microbes (PGPMs) that can further facilitate
the development of a more promising bioremediation strategy (Tak et al. 2013). The
efficacy of phytoremediation is limited by the major factors, such as, tolerance level
for the contaminant by the plant, selection of the plant variety to be employed for
bioremediation, and its capacity to uptake and translocate the heavy metals (Jutsz
and Gnida 2015). Phytoremediation, as indicated earlier, is an economically feasible
bioremediation strategy as it produces the utilisable biomass while removing the
toxic metals (Angelova et al. 2016).
Most plant species harbour vesicular-arbuscular mycorrhizae (VAM) that primarily help in phosphate solubilisation and uptake thereby enhancing their stress
tolerance ability (Sharma et al. 2017). Upadhyay et al. (2018) reported that VAM
supplementation helped overcome arsenic-induced phosphate deficiency in wheat.
VAM also helps in maintaining a good ratio of arsenic and phosphate by
translocating arsenic to inside the plant cells, particularly in soils with low arsenic
contamination. In a similar study, Li et al. (2016) observed a decrease in the
8 Arsenic Contamination: Sources, Chemistry and Remediation Strategies
231