root-colonizing pollutant-degrading bacteria on a suitable crop plant resulted in
improved bioremediation of the pesticide. The niche combination of plant and
microorganisms led to the effective degradation of naphthalene and protected the
grass seeds against the toxic concentrations of naphthalene. In another soil, contaminated with creosote, on inoculation of tall fescue (Festuca arundinacea) with
polycyclic aromatic hydrocarbons (PAH) degrading bacteria and PGPB (Pseudomonas putida, A. brasilense, and Enterobacter cloacae) substantially increased the
removal rate of PAH (Guo et al. 2018). Large-sized PAH were eliminated in the
presence of these PGPB because these specific bacterial species reduced stress in
plants through ACC-deaminase activity (Huang et al. 2004). Pseudomonas spp. have
been reported to increase the growth of the canola plant and common weed Phragmites australis in the presence of copper or PAH (Reed and Glick 2005; Reed et al.
2005). PGPB degraded 2-chlorobenzoic acid and oil-contaminated soils for growing
Vicia faba and many forage grasses, but no clear relationship between contaminant
disappearance of pollutants and enhanced plant biomass was observed (Siciliano and
Germida 1997; Radwan et al. 2005). The bioremediation potential of legumes
Galega orientalis and its symbiont, Rhizobium galegae, has been assessed in soils
contaminated with benzene, toluene, and/or xylene (BTX). The Galega plants
showed good growth, nodulation, and nitrogen fixation in soils contaminated with
oil or spiked with m-toluate, a model compound representing BTX (Suominen et al.
2000).
Several endophytic bacteria were also found to help host plants overcome
contaminant-induced stress, and resulted in improved plant growth (Correa-Galeote
et al. 2018). During phytoremediation of organic contaminants in soils, plants benefit
more from their endophytes, which have degenerative pathways and metabolic
abilities that are not inherent in the plant. This strategy leads to a more effective
degradation and reduction of phytotoxicity and evaporation of volatile contaminants
(Weyens et al. 2009). For example, tall fescue Festuca arundinacea grass selects the
prevalence of endophytes containing pollutant catabolic genes in an environment
contaminated with different pollutants (hydrocarbons and nitro-aromatics) (Siciliano
et al. 2001). Barac et al. (2009) reported that when remediation reduced BTX below
a detectable level, the ability of the endophytic community in poplar plants to
degrade BTX disappeared. Similarly, inoculation of the Pisum sativum plant with
an endophyte (isolated from poplar), having the capability to degrade the herbicide
2,4-D, increased the removal of 2,4-D from the soil (Germaine et al. 2006).
The excretion of root exudates may also stimulate growth of specific, pollutantdegrading bacteria in the rhizosphere by secreting phospholipid surfactants (Sindhu
et al. 2017) that make organic pollutants more bioavailable or by releasing secondary
metabolites that induce the expression of genes with organic pollutant-degradation
potential (Pilon-Smits 2005). For example, Rhodococcus species are the most
common group in the rhizosphere of trees, which naturally colonized and improved
a PCB-contaminated site in the Czech Republic (Van der Geize and Dijkhuizen
2004). Barley growing in PAH-contaminated soils has contributed to the growth of
Mycobacterium species capable of mineralizing the PAH (Child et al. 2007). Soils
contaminated with petroleum derivatives generally have high concentrations of
2 Bioremediation of Pesticides: An Eco-Friendly Approach for Environment. . .
47
improved bioremediation of the pesticide. The niche combination of plant and
microorganisms led to the effective degradation of naphthalene and protected the
grass seeds against the toxic concentrations of naphthalene. In another soil, contaminated with creosote, on inoculation of tall fescue (Festuca arundinacea) with
polycyclic aromatic hydrocarbons (PAH) degrading bacteria and PGPB (Pseudomonas putida, A. brasilense, and Enterobacter cloacae) substantially increased the
removal rate of PAH (Guo et al. 2018). Large-sized PAH were eliminated in the
presence of these PGPB because these specific bacterial species reduced stress in
plants through ACC-deaminase activity (Huang et al. 2004). Pseudomonas spp. have
been reported to increase the growth of the canola plant and common weed Phragmites australis in the presence of copper or PAH (Reed and Glick 2005; Reed et al.
2005). PGPB degraded 2-chlorobenzoic acid and oil-contaminated soils for growing
Vicia faba and many forage grasses, but no clear relationship between contaminant
disappearance of pollutants and enhanced plant biomass was observed (Siciliano and
Germida 1997; Radwan et al. 2005). The bioremediation potential of legumes
Galega orientalis and its symbiont, Rhizobium galegae, has been assessed in soils
contaminated with benzene, toluene, and/or xylene (BTX). The Galega plants
showed good growth, nodulation, and nitrogen fixation in soils contaminated with
oil or spiked with m-toluate, a model compound representing BTX (Suominen et al.
2000).
Several endophytic bacteria were also found to help host plants overcome
contaminant-induced stress, and resulted in improved plant growth (Correa-Galeote
et al. 2018). During phytoremediation of organic contaminants in soils, plants benefit
more from their endophytes, which have degenerative pathways and metabolic
abilities that are not inherent in the plant. This strategy leads to a more effective
degradation and reduction of phytotoxicity and evaporation of volatile contaminants
(Weyens et al. 2009). For example, tall fescue Festuca arundinacea grass selects the
prevalence of endophytes containing pollutant catabolic genes in an environment
contaminated with different pollutants (hydrocarbons and nitro-aromatics) (Siciliano
et al. 2001). Barac et al. (2009) reported that when remediation reduced BTX below
a detectable level, the ability of the endophytic community in poplar plants to
degrade BTX disappeared. Similarly, inoculation of the Pisum sativum plant with
an endophyte (isolated from poplar), having the capability to degrade the herbicide
2,4-D, increased the removal of 2,4-D from the soil (Germaine et al. 2006).
The excretion of root exudates may also stimulate growth of specific, pollutantdegrading bacteria in the rhizosphere by secreting phospholipid surfactants (Sindhu
et al. 2017) that make organic pollutants more bioavailable or by releasing secondary
metabolites that induce the expression of genes with organic pollutant-degradation
potential (Pilon-Smits 2005). For example, Rhodococcus species are the most
common group in the rhizosphere of trees, which naturally colonized and improved
a PCB-contaminated site in the Czech Republic (Van der Geize and Dijkhuizen
2004). Barley growing in PAH-contaminated soils has contributed to the growth of
Mycobacterium species capable of mineralizing the PAH (Child et al. 2007). Soils
contaminated with petroleum derivatives generally have high concentrations of
2 Bioremediation of Pesticides: An Eco-Friendly Approach for Environment. . .
47