46
A. Dahiya et al.
assimilating solubilized phosphorus (Khan and Joergensen 2009). Thus, endophytic
bacteria can act as a sink to provide need-based phosphorus to the plants.
3.5.1 Phosphate Solubilization by Endophytic Bacteria
Phosphate solubilization feature is commonly found in endophytic bacteria. About
59–100% of endophytic populations obtained form cactus, strawberry, sunflower,
soybean, and other legumes were found to possess the ability to solubilize phosphate (Kuklinsky-Sobral et al. 2004; Forchetti et al. 2007; Dias et al. 2009; Puente
et al. 2009a; Palaniappan et al. 2010). The role of phosphate solubilizing endophytic
bacteria was established by growing bacteria-free cacti on mineral phosphate supplemented with either endophytes or nutrients, and these plants were compared with
plants grown under sterile conditions (Puente et al. 2009b). The growth of inoculated
plants without nutrient addition was comparable to the fertilized plants, whereas the
bacteria-free unfertilized cacti failed to grow. These results suggested that endophytic
bacteria provided the developing plantlets with the limiting nutrient phosphorus.
Longback, Gaur (1990) observed a gradual increase of available P and acidity
of the medium up to a certain period by Pseudomonas striata, the available P level
corresponded with an increase of pH to a certain extent. Many phosphate solubilizing microbes are responsible for the production of organic acids and gluconic
acid is known as the principal organic acid for mineral phosphate solubilization..
The highest phosphate solubilization capacity was observed in isolates EB-47 and
EB-64 (Bacillus sp. and Bacillus pumilus). The isolate EB-53 (Lysinibacillus sp.)
showed high solubilization index, whereas 73% of the isolates showed low solubilization indices. These endophytic bacteria were subsequently used as growthpromoting microbial inoculants in nurseries growing banana suckers (Andrade et al.
2014). Endophytic isolates of P. fluorescens were obtained from the silver grass
(Miscanthus giganteus) crop (Oteino et al. 2013). Maximum phosphate solubilization was recorded in P. fluorescens strain L228 and Pseudomonas sp. strain L132 in
comparison to negative control E. coli JM109. All strains showed the production of
gibberellic acid (GA) with a concentration ranging from 2840 to 33240 ± 230 mg
L
−1 (14–169 mM).
Kumar et al. (2013) isolated root endophytes from nodules of legume plants. Large
numbers of Gram-positive bacterial endophytes were present in legume nodules than
in its roots, which showed 56 and 47.8% phosphate solubilizing ability, respectively.
From legume roots, 56.9% isolates showed phosphate solubilizing activity, whereas
only 35.9% showed from non-legume roots. Moreover, the highest numbers of phosphate solubilizing isolates (73.3%) were observed from field pea roots and the lowest
numbers of phosphate solubilizing isolates (20%) were observed in oat roots. The
amount of P solubilization was higher in isolates from chickpea than oat roots. The
significant phosphate solubilizing bacterial isolates were obtained from legume roots
and nodules (CRE1 and CNE215) and non-legume roots (WRE10, WRE20, and
A. Dahiya et al.
assimilating solubilized phosphorus (Khan and Joergensen 2009). Thus, endophytic
bacteria can act as a sink to provide need-based phosphorus to the plants.
3.5.1 Phosphate Solubilization by Endophytic Bacteria
Phosphate solubilization feature is commonly found in endophytic bacteria. About
59–100% of endophytic populations obtained form cactus, strawberry, sunflower,
soybean, and other legumes were found to possess the ability to solubilize phosphate (Kuklinsky-Sobral et al. 2004; Forchetti et al. 2007; Dias et al. 2009; Puente
et al. 2009a; Palaniappan et al. 2010). The role of phosphate solubilizing endophytic
bacteria was established by growing bacteria-free cacti on mineral phosphate supplemented with either endophytes or nutrients, and these plants were compared with
plants grown under sterile conditions (Puente et al. 2009b). The growth of inoculated
plants without nutrient addition was comparable to the fertilized plants, whereas the
bacteria-free unfertilized cacti failed to grow. These results suggested that endophytic
bacteria provided the developing plantlets with the limiting nutrient phosphorus.
Longback, Gaur (1990) observed a gradual increase of available P and acidity
of the medium up to a certain period by Pseudomonas striata, the available P level
corresponded with an increase of pH to a certain extent. Many phosphate solubilizing microbes are responsible for the production of organic acids and gluconic
acid is known as the principal organic acid for mineral phosphate solubilization..
The highest phosphate solubilization capacity was observed in isolates EB-47 and
EB-64 (Bacillus sp. and Bacillus pumilus). The isolate EB-53 (Lysinibacillus sp.)
showed high solubilization index, whereas 73% of the isolates showed low solubilization indices. These endophytic bacteria were subsequently used as growthpromoting microbial inoculants in nurseries growing banana suckers (Andrade et al.
2014). Endophytic isolates of P. fluorescens were obtained from the silver grass
(Miscanthus giganteus) crop (Oteino et al. 2013). Maximum phosphate solubilization was recorded in P. fluorescens strain L228 and Pseudomonas sp. strain L132 in
comparison to negative control E. coli JM109. All strains showed the production of
gibberellic acid (GA) with a concentration ranging from 2840 to 33240 ± 230 mg
L
−1 (14–169 mM).
Kumar et al. (2013) isolated root endophytes from nodules of legume plants. Large
numbers of Gram-positive bacterial endophytes were present in legume nodules than
in its roots, which showed 56 and 47.8% phosphate solubilizing ability, respectively.
From legume roots, 56.9% isolates showed phosphate solubilizing activity, whereas
only 35.9% showed from non-legume roots. Moreover, the highest numbers of phosphate solubilizing isolates (73.3%) were observed from field pea roots and the lowest
numbers of phosphate solubilizing isolates (20%) were observed in oat roots. The
amount of P solubilization was higher in isolates from chickpea than oat roots. The
significant phosphate solubilizing bacterial isolates were obtained from legume roots
and nodules (CRE1 and CNE215) and non-legume roots (WRE10, WRE20, and