12
Bk7 prominently shows the intrinsic mechanism of phosphate solubilization, IAA,
siderophore, and ammonia production, and biofilm formation. Certain antimicrobial
peptide genes such as srfAA, fenD, bmyB, bacA, and ituC showed higher expression in B. amyloliquefaciens Bk7 during pathogen exposure (Kakar et al. 2014). The
mechanism of Rhizoctonia solani-mediated sheath blight disease of rice was
explained by surfactin (srfA-A), the bacillomycin L (bacD) gene mutant, and
srf + bac double mutants of Bacillus subtilis 916. In all the mutants, surfactin and
bacillomycin L production decreases with reduced swarming motility, biofilm formation, and colonization of the rice sheaths. Such biofilm conserves the root exudates for the host plant health and protects it from the soil-borne pathogens
(Beauregard et al. 2013). Mutant (srfA-A) is not able to restore biofilm formation
with exogenous surfactin supplement (Zeriouh et al. 2014), whereas bacD mutant
can form biofilm upon surfactin or bacillomycin L addition, indicating that the synergistic effect of surfactin and bacillomycin L is necessary for plant health (Luo
et al. 2014). The lepidopeptide-mediated biocontrol via antibacterial activity can
also activate induced systemic response in the host plant (Zaman and Toth 2013).
Plant- associated microbes such as Pseudomonas sp. and Chryseobacterium sp. have
the capacity to provide protection against biotic (Xanthomonas campestris pv. oryzae) and abiotic (salt; 3.5 g/l
−1
in substrate) stress by activation of the induced systemic resistance (Lucas et al. 2014).
Microbial interactions with a wheat crop have an important role in disease suppression. Pseudomonas fluorescens HC1-07 suppresses the causal organisms of root
rot and take-all of wheat, Rhizoctonia solani AG-8 and Gaeumannomyces graminis
var. tritici, respectively. Disease suppression was regulated by the production of
cyclic lipopeptides (CLP). Mutant studies reveal that the prtR and viscB genes are
involved in the production of the viscosin-like CLP. The gene prtR has an additional
trait of protease production that improves the defence system of the plants (Yang
et al. 2014). Pseudomonas fluorescens further inhibits the growth of Botrytis cinerea, a phytopathogen in Medicago truncatula (Hernández-León et al. 2015). ACCdeaminase, siderophores, indole-3-acetic acid, phenazines, cyanogens, and proteases
produced by P. fluorescens are signatory molecules for supporting PGP and plant
health. P. fluorescens also has the ability to form A biofilm and secrete antifungal
volatile organic compounds (VOCs), such as dimethyl disulfide, which has a proven
role in plant defence (Huang et al. 2012). Thus, in any systematic approach, knowledge of soil microorganism biofilms, VOCs, and signalling in combination with
plants is necessary for better crop health and improved agro-ecological services for
sustainable agro-ecosystems (McGenity et al. 2018) (Table 2.1).
2.6 Microorganisms Improve Soil Quality
Soil is a living dynamic system that supports terrestrial life on Earth. There has been
a steady and serious decline in soil health because of heavy use of agrochemicals,
deforestation, and unregulated release of pollutants to the soil (Lehman et al. 2015).
2 Belowground Microbial Communities: Key Players for Soil and Environmental…
Bk7 prominently shows the intrinsic mechanism of phosphate solubilization, IAA,
siderophore, and ammonia production, and biofilm formation. Certain antimicrobial
peptide genes such as srfAA, fenD, bmyB, bacA, and ituC showed higher expression in B. amyloliquefaciens Bk7 during pathogen exposure (Kakar et al. 2014). The
mechanism of Rhizoctonia solani-mediated sheath blight disease of rice was
explained by surfactin (srfA-A), the bacillomycin L (bacD) gene mutant, and
srf + bac double mutants of Bacillus subtilis 916. In all the mutants, surfactin and
bacillomycin L production decreases with reduced swarming motility, biofilm formation, and colonization of the rice sheaths. Such biofilm conserves the root exudates for the host plant health and protects it from the soil-borne pathogens
(Beauregard et al. 2013). Mutant (srfA-A) is not able to restore biofilm formation
with exogenous surfactin supplement (Zeriouh et al. 2014), whereas bacD mutant
can form biofilm upon surfactin or bacillomycin L addition, indicating that the synergistic effect of surfactin and bacillomycin L is necessary for plant health (Luo
et al. 2014). The lepidopeptide-mediated biocontrol via antibacterial activity can
also activate induced systemic response in the host plant (Zaman and Toth 2013).
Plant- associated microbes such as Pseudomonas sp. and Chryseobacterium sp. have
the capacity to provide protection against biotic (Xanthomonas campestris pv. oryzae) and abiotic (salt; 3.5 g/l
−1
in substrate) stress by activation of the induced systemic resistance (Lucas et al. 2014).
Microbial interactions with a wheat crop have an important role in disease suppression. Pseudomonas fluorescens HC1-07 suppresses the causal organisms of root
rot and take-all of wheat, Rhizoctonia solani AG-8 and Gaeumannomyces graminis
var. tritici, respectively. Disease suppression was regulated by the production of
cyclic lipopeptides (CLP). Mutant studies reveal that the prtR and viscB genes are
involved in the production of the viscosin-like CLP. The gene prtR has an additional
trait of protease production that improves the defence system of the plants (Yang
et al. 2014). Pseudomonas fluorescens further inhibits the growth of Botrytis cinerea, a phytopathogen in Medicago truncatula (Hernández-León et al. 2015). ACCdeaminase, siderophores, indole-3-acetic acid, phenazines, cyanogens, and proteases
produced by P. fluorescens are signatory molecules for supporting PGP and plant
health. P. fluorescens also has the ability to form A biofilm and secrete antifungal
volatile organic compounds (VOCs), such as dimethyl disulfide, which has a proven
role in plant defence (Huang et al. 2012). Thus, in any systematic approach, knowledge of soil microorganism biofilms, VOCs, and signalling in combination with
plants is necessary for better crop health and improved agro-ecological services for
sustainable agro-ecosystems (McGenity et al. 2018) (Table 2.1).
2.6 Microorganisms Improve Soil Quality
Soil is a living dynamic system that supports terrestrial life on Earth. There has been
a steady and serious decline in soil health because of heavy use of agrochemicals,
deforestation, and unregulated release of pollutants to the soil (Lehman et al. 2015).
2 Belowground Microbial Communities: Key Players for Soil and Environmental…