case of firmicutes, they are the silent member in case of N 2 fixation, potassium
solubilisation, ammonia and HCN production. However, the firmicutes have
exhibited ACC activity, P-solubilisation, siderophore activity and IAA production
(Fig. 22.6).
22.4 Genetically Modified Plant Growth-Promoting
Rhizobacteria for Crop Enhancement
Natural components like the PGPR play an indispensable role in the advancement of
sustainable agriculture and also serve as an imperishable treasure box for the
environment. Considering the limitations of these natural bio-agents, the idea of
using genetic modification approaches has attracted the attention of scientists with
the goal of attaining greater desired efficiency. With the improvements achieved by
genetically engineering PGPR, the heavy metal accumulating gene and the
biocontrolling genes can be assembled to conduct enhanced bioremediation and
potentially achieve biocontrol in the rhizospheric soil. In this context, for superior
cadmium (Cd
2+ ) bioaccumulation purpose, the phytochelatin synthase gene (PCS AT )
from Arabidopsis thaliana was introduced into Mesorhizobium huakuii strain B3
and then set up as a symbiosis with M. huakuii strain B3 and Astragalus sinicus,
whereupon a desired activity was noted accordingly (Sriprang et al. 2003). It was
possible to carry out that project because the peptides like phytochelatins (PC) and
metallothioneins (MT) exhibit high affinity towards a variety of heavy metals
(Chaudhary and Shukla 2019). Furthermore, genetically transformed rhizobacterial
strains demonstrated significant biocontrol potentiality over fungal phytopathogens
(Sattiraju et al. 2019). In such cases, incorporation of a mini-Tn5 vector containing
the complete operon for the biosynthesis of an antifungal metabolite phenazine- 1carboxylic acid (PCA), within Pseudomonas fluorescens has been documented to
accelerate the suppression of fungal diseases by the genetically engineered bacterial
strain in comparison to the natural bacterial strain (Timms-Wilson et al. 2000).
Similar kinds of approaches were reported from several studies where genetically
engineered PGPR strains showed enhanced PGP traits as well as biocontrol efficiency (Bloemberg and Lugtenberg 2001) and can be exemplified by the integration
of Cry-toxin-encoding cry1Ac7 gene from Bacillus thuringiensis, chitinaseencoding chiA gene from Serratia marcescens and ACC deaminase-producing
gene from Enterobacter cloacae into rhizobacterial strains like Pseudomonas
sp. (Sattiraju et al. 2019). The relocation of sss gene from biocontrol strain P.
fluorescens WCS365 to other P. fluorescens rhizobacterial strains was found to
improve the competitive root colonising efficiency (Dekkers et al. 2000). Apart
from the genetically modified PGPR, transgenic plants also display greater PGP
traits, especially higher ACC deaminase activity and heavy metal accumulation
(Zhuang et al. 2007; Stearns et al. 2005; Nie et al. 2002). However, genetically
modified PGPB are considered less effective in terms of their survival and
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K. Pramanik et al.
solubilisation, ammonia and HCN production. However, the firmicutes have
exhibited ACC activity, P-solubilisation, siderophore activity and IAA production
(Fig. 22.6).
22.4 Genetically Modified Plant Growth-Promoting
Rhizobacteria for Crop Enhancement
Natural components like the PGPR play an indispensable role in the advancement of
sustainable agriculture and also serve as an imperishable treasure box for the
environment. Considering the limitations of these natural bio-agents, the idea of
using genetic modification approaches has attracted the attention of scientists with
the goal of attaining greater desired efficiency. With the improvements achieved by
genetically engineering PGPR, the heavy metal accumulating gene and the
biocontrolling genes can be assembled to conduct enhanced bioremediation and
potentially achieve biocontrol in the rhizospheric soil. In this context, for superior
cadmium (Cd
2+ ) bioaccumulation purpose, the phytochelatin synthase gene (PCS AT )
from Arabidopsis thaliana was introduced into Mesorhizobium huakuii strain B3
and then set up as a symbiosis with M. huakuii strain B3 and Astragalus sinicus,
whereupon a desired activity was noted accordingly (Sriprang et al. 2003). It was
possible to carry out that project because the peptides like phytochelatins (PC) and
metallothioneins (MT) exhibit high affinity towards a variety of heavy metals
(Chaudhary and Shukla 2019). Furthermore, genetically transformed rhizobacterial
strains demonstrated significant biocontrol potentiality over fungal phytopathogens
(Sattiraju et al. 2019). In such cases, incorporation of a mini-Tn5 vector containing
the complete operon for the biosynthesis of an antifungal metabolite phenazine- 1carboxylic acid (PCA), within Pseudomonas fluorescens has been documented to
accelerate the suppression of fungal diseases by the genetically engineered bacterial
strain in comparison to the natural bacterial strain (Timms-Wilson et al. 2000).
Similar kinds of approaches were reported from several studies where genetically
engineered PGPR strains showed enhanced PGP traits as well as biocontrol efficiency (Bloemberg and Lugtenberg 2001) and can be exemplified by the integration
of Cry-toxin-encoding cry1Ac7 gene from Bacillus thuringiensis, chitinaseencoding chiA gene from Serratia marcescens and ACC deaminase-producing
gene from Enterobacter cloacae into rhizobacterial strains like Pseudomonas
sp. (Sattiraju et al. 2019). The relocation of sss gene from biocontrol strain P.
fluorescens WCS365 to other P. fluorescens rhizobacterial strains was found to
improve the competitive root colonising efficiency (Dekkers et al. 2000). Apart
from the genetically modified PGPR, transgenic plants also display greater PGP
traits, especially higher ACC deaminase activity and heavy metal accumulation
(Zhuang et al. 2007; Stearns et al. 2005; Nie et al. 2002). However, genetically
modified PGPB are considered less effective in terms of their survival and
470
K. Pramanik et al.