from contaminated matrix (Ali et al. 2013; Chandra et al. 2015; Mahar et al. 2016;
Sarwar et al. 2017). However, extensive research is currently underway to testify the
phytoremediation potential of hyperaccumulating plants in the field for the effective
treatment and management of HM-contaminated sites.
Further, exploiting plant-associated microbes with desired traits to enhance the
phytoremediation efficiency of hyperaccumulating plants via increasing the bioavailability of metals in soil and plant growth promotion in the stressed environment
is termed as microbe-assisted phytoremediation. Inoculation of plants with plant
growth-promoting bacteria (PGPR) may be helpful in phytoremediation as they can
suppress phytopathogens, tolerate abiotic stress and lowers the metal toxicity to
remediating plants through biosorption/bioaccumulation as bacterial cells have
extremely high ratio of surface area to volume as well as promote plant growth by
secreting various hormones, organic acids, and antibiotics (Rajkumar et al. 2012;
Ullah et al. 2015). Endophytes are also able to tolerate high metals concentration and
hence, lower phytotoxicity to remediating plants and helps in growth promotion by
various means and thus, enhance phytoremediation efficiency (Ma et al. 2011,
2015). In addition, arbuscular mycorrhizal fungi (AMF, colonize plant roots) have
been also reported to protect their host plants against heavy metal toxicity through
their mobilization from soil, thus helping in the phytoremediation (Marques et al.
2009; Khan et al. 2014). A great deal of literature can be found in the public domain
on the microbe-assisted phytoremediation of heavy metals (Khan et al. 2014; Ma
et al. 2011, 2015; Rajkumar et al. 2012; Ullah et al. 2015). Further, to ameliorate
metal toxicity, plant growth promotion, and metal sequestration, extensive research
efforts are also required to explore novel microbial diversity and their distribution, as
well as functions in the autochthonous and allochthonous soil habitats for microbeassisted phytoremediation of HM-contaminated sites.
Several examples are existing on the phytoremediation and microbe-assisted
phytoremediation of pollutants from industrial wastewaters. For instance, Gupta
et al. (2018) studied the microbe-assisted phytoremediation of tannery wastewater
(TWW) contaminated agricultural soils. They isolated a Cr
6+ -resistant plant growthpromoting Pseudomonas sp. (strain CPSB21) from the tannery effluent contaminated agricultural soils and evaluated for the various plant growth-promoting activities, oxidative stress tolerance, and Cr
6+ bioremediation. Further, they applied the
isolated strain for microbe-assisted phytoremediation and reported that the inoculation of strain CPSB21 alleviated the Cr
6+ toxicity and enhanced the plant growth
parameters and nutrient uptake in sunflower plant during pot experiment. Kassaye
et al. (2017) reported the phytoremediation potential of swamp smartweed (Polygonum coccineum), Para grass (Brachiaria mutica), and papyrus (Cyperus papyrus)
for Cr-containing TWW. They reported that all the three plants exhibited a significant transfer of Cr from wastewater (phytoextraction) to roots and shoots, but
removal efficiency of Cr for swamp smartweed was relatively low as compared to
Para grass and papyrus and further suggested the use of Para grass and papyrus for
effective phytoremediation of TWW. Gregorio et al. (2015) reported the bacterialassisted phytoremediation of organic pollutants in TWW received from a conventional tannery wastewater treatment plant. They bioaugmented a plant growth116
G. Saxena et al.
Sarwar et al. 2017). However, extensive research is currently underway to testify the
phytoremediation potential of hyperaccumulating plants in the field for the effective
treatment and management of HM-contaminated sites.
Further, exploiting plant-associated microbes with desired traits to enhance the
phytoremediation efficiency of hyperaccumulating plants via increasing the bioavailability of metals in soil and plant growth promotion in the stressed environment
is termed as microbe-assisted phytoremediation. Inoculation of plants with plant
growth-promoting bacteria (PGPR) may be helpful in phytoremediation as they can
suppress phytopathogens, tolerate abiotic stress and lowers the metal toxicity to
remediating plants through biosorption/bioaccumulation as bacterial cells have
extremely high ratio of surface area to volume as well as promote plant growth by
secreting various hormones, organic acids, and antibiotics (Rajkumar et al. 2012;
Ullah et al. 2015). Endophytes are also able to tolerate high metals concentration and
hence, lower phytotoxicity to remediating plants and helps in growth promotion by
various means and thus, enhance phytoremediation efficiency (Ma et al. 2011,
2015). In addition, arbuscular mycorrhizal fungi (AMF, colonize plant roots) have
been also reported to protect their host plants against heavy metal toxicity through
their mobilization from soil, thus helping in the phytoremediation (Marques et al.
2009; Khan et al. 2014). A great deal of literature can be found in the public domain
on the microbe-assisted phytoremediation of heavy metals (Khan et al. 2014; Ma
et al. 2011, 2015; Rajkumar et al. 2012; Ullah et al. 2015). Further, to ameliorate
metal toxicity, plant growth promotion, and metal sequestration, extensive research
efforts are also required to explore novel microbial diversity and their distribution, as
well as functions in the autochthonous and allochthonous soil habitats for microbeassisted phytoremediation of HM-contaminated sites.
Several examples are existing on the phytoremediation and microbe-assisted
phytoremediation of pollutants from industrial wastewaters. For instance, Gupta
et al. (2018) studied the microbe-assisted phytoremediation of tannery wastewater
(TWW) contaminated agricultural soils. They isolated a Cr
6+ -resistant plant growthpromoting Pseudomonas sp. (strain CPSB21) from the tannery effluent contaminated agricultural soils and evaluated for the various plant growth-promoting activities, oxidative stress tolerance, and Cr
6+ bioremediation. Further, they applied the
isolated strain for microbe-assisted phytoremediation and reported that the inoculation of strain CPSB21 alleviated the Cr
6+ toxicity and enhanced the plant growth
parameters and nutrient uptake in sunflower plant during pot experiment. Kassaye
et al. (2017) reported the phytoremediation potential of swamp smartweed (Polygonum coccineum), Para grass (Brachiaria mutica), and papyrus (Cyperus papyrus)
for Cr-containing TWW. They reported that all the three plants exhibited a significant transfer of Cr from wastewater (phytoextraction) to roots and shoots, but
removal efficiency of Cr for swamp smartweed was relatively low as compared to
Para grass and papyrus and further suggested the use of Para grass and papyrus for
effective phytoremediation of TWW. Gregorio et al. (2015) reported the bacterialassisted phytoremediation of organic pollutants in TWW received from a conventional tannery wastewater treatment plant. They bioaugmented a plant growth116
G. Saxena et al.