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D. Ghosh et al.
1 Introduction
Heavy metals are omnipresent in diverse chemical states in the ecosystem. The
ecosystem has been contaminated by several anthropogenic activities likely municipal, agricultural, industrial, and mining waste effluent disposals, which are highly
impoverished with toxic heavy metals. Animal and plants are both directly or indirectly intoxicated due to vulnerability of these heavy metals that are present in
contaminated rhizosphere, water supplies, and foods, respectively (Mishra et al. 2017;
Rana et al. 2018). Among several heavy metals, cadmium (Cd) and mercury (Hg) are
considered as highly toxic threat to environment and human health (Chibuike and
Obiora 2014; Henkler et al. 2010). Heavy metal stress induces several alterations
in plant physiology and metabolic activities in a dose-dependent manner. These
heavy metals especially cadmium and mercury compete with essential micronutrients (potassium, phosphorous, and zinc) absorption by root in plant bodies and
cause nutrient deficiency (Zhuang et al. 2014). Cadmium heavily inhibits chlorophyll
content, photosynthetic rate, photosystems II quantum yield, stomatal conductance,
and intracellular carbon dioxide assimilation (hindering Rubisco enzymatic activity).
It causes immense influence on nitrate metabolism by inhibition of nitrate uptake,
nitrate transportation. Cadmium induces protease activity; it reduces metabolic efficacy of nitrate metabolizing enzymes (i.e., nitrate reductases, nitrite reductases) and
ammonia-assimilating enzymes (i.e., glutamine synthetase, glutamine oxoglutarate
aminotransferases, and glutamate dehydrogenase) (Singh et al. 2016). Cadmium
generates reactive oxygen species (ROS) in respective organelles, i.e., chloroplast,
mitochondria, and peroxisomes via reduction in the photosynthetic electron transport chain and disturbances in carbon dioxide sequestrations (Mittler et al. 2004).
Mercury is abundant in nature and has enormous effect on kidney, causing proteinuria (Reyes et al. 2013). Extensive exposure to mercury can increase the possibility
of immune, sensory, neurological dysfunctions having similar symptoms of autism
spectrum disorders. Moreover, mercury affects antioxidants in the cellular system that
enhances loss of membrane integrity and cellular necrosis (Abdel 2015). Mercury
deposition induces ROS generation, mRNA expression of metallothionein, apoptosis, and proximal tubule damage (Agarwal et al. 2010). An alternative molecular
mechanism includes an increase in hydrogen peroxide concentration after mercury
exposure, which hampers glutathione antioxidant network. Moreover, mercury also
increases hydrogen peroxide level in brain and lipid peroxidation (Farina et al. 2011).
Therefore, it is an urgent need for real-time monitoring of minimal level of heavy
metals in our ecosystem to minimize heavy metal toxicity toward environment and
human health hazards. Different spectroscopy, chromatography, and ion-sensitive
techniques are in practice at present for heavy metal detections. However, these
current approaches suffer due to lower electrode selectivity, inaccurate response,
higher cost, and nonreal-time monitoring. Algal alkaline phosphatases (APs) (EC
3.1.3.1) are the class of hydrolase, which transform phosphoester molecules into
soluble inorganic phosphate. However, catalytic efficacies of APs have strongly been
inhibited in the presence of trace amount of heavy metals. This particular feature of
D. Ghosh et al.
1 Introduction
Heavy metals are omnipresent in diverse chemical states in the ecosystem. The
ecosystem has been contaminated by several anthropogenic activities likely municipal, agricultural, industrial, and mining waste effluent disposals, which are highly
impoverished with toxic heavy metals. Animal and plants are both directly or indirectly intoxicated due to vulnerability of these heavy metals that are present in
contaminated rhizosphere, water supplies, and foods, respectively (Mishra et al. 2017;
Rana et al. 2018). Among several heavy metals, cadmium (Cd) and mercury (Hg) are
considered as highly toxic threat to environment and human health (Chibuike and
Obiora 2014; Henkler et al. 2010). Heavy metal stress induces several alterations
in plant physiology and metabolic activities in a dose-dependent manner. These
heavy metals especially cadmium and mercury compete with essential micronutrients (potassium, phosphorous, and zinc) absorption by root in plant bodies and
cause nutrient deficiency (Zhuang et al. 2014). Cadmium heavily inhibits chlorophyll
content, photosynthetic rate, photosystems II quantum yield, stomatal conductance,
and intracellular carbon dioxide assimilation (hindering Rubisco enzymatic activity).
It causes immense influence on nitrate metabolism by inhibition of nitrate uptake,
nitrate transportation. Cadmium induces protease activity; it reduces metabolic efficacy of nitrate metabolizing enzymes (i.e., nitrate reductases, nitrite reductases) and
ammonia-assimilating enzymes (i.e., glutamine synthetase, glutamine oxoglutarate
aminotransferases, and glutamate dehydrogenase) (Singh et al. 2016). Cadmium
generates reactive oxygen species (ROS) in respective organelles, i.e., chloroplast,
mitochondria, and peroxisomes via reduction in the photosynthetic electron transport chain and disturbances in carbon dioxide sequestrations (Mittler et al. 2004).
Mercury is abundant in nature and has enormous effect on kidney, causing proteinuria (Reyes et al. 2013). Extensive exposure to mercury can increase the possibility
of immune, sensory, neurological dysfunctions having similar symptoms of autism
spectrum disorders. Moreover, mercury affects antioxidants in the cellular system that
enhances loss of membrane integrity and cellular necrosis (Abdel 2015). Mercury
deposition induces ROS generation, mRNA expression of metallothionein, apoptosis, and proximal tubule damage (Agarwal et al. 2010). An alternative molecular
mechanism includes an increase in hydrogen peroxide concentration after mercury
exposure, which hampers glutathione antioxidant network. Moreover, mercury also
increases hydrogen peroxide level in brain and lipid peroxidation (Farina et al. 2011).
Therefore, it is an urgent need for real-time monitoring of minimal level of heavy
metals in our ecosystem to minimize heavy metal toxicity toward environment and
human health hazards. Different spectroscopy, chromatography, and ion-sensitive
techniques are in practice at present for heavy metal detections. However, these
current approaches suffer due to lower electrode selectivity, inaccurate response,
higher cost, and nonreal-time monitoring. Algal alkaline phosphatases (APs) (EC
3.1.3.1) are the class of hydrolase, which transform phosphoester molecules into
soluble inorganic phosphate. However, catalytic efficacies of APs have strongly been
inhibited in the presence of trace amount of heavy metals. This particular feature of