Isolation and Characterization of Rhizosphere-Competent Indigenous Phosphate-Solubilizing Bacteria for Biofertilizer Applications

Abstract

Phosphorus (P) is an essential nutrient for crop growth and development. Low levels of P in soil is due to high reactivity of soluble P with calcium (Ca), iron (Fe) or aluminum (Al) that lead to P precipitation. Mineral phosphate (P) solubilization is an important activity of rhizospheric bacteria that contribute significantly to the plant growth and development in eco-friendly manner. Four potent phosphate solubilizers (PSB-2, PSB-3, PSB-4 and PSB-7), which effectively solubilize aluminum phosphate, iron phosphate, tri-calcium phosphate, rock phosphate through organic acid production mechanism under buffering conditions, were isolated. On the basis of morphological, biochemical and molecular analyses, it is confirmed that all the isolates belong to gamma-Proteobacteriaceae order and Enterobacteriaceae family. Four efficient phosphate solubilizers were identified as PSB-2 (Enterobacter sp.), PSB-3 (Pantoea sp.) PSB-4 (Pantoea sp.) and PSB-7 (Enterobacter sp.), and proceeded for further characterization studies. Production of organic acids and subsequent pH drop have been found as chief mechanism for P solubilization in this study. Gluconic acid, xylonic acid and formic acid are the chief organic acids produced by these four PSBs. Xylose was the preferred substrate over glucose for activity of metabolic enzymes GDH, G6PDH and PFL (pyruvate formate lyase ). Different PGPR traits were studied and the results showed that all the four isolates were found to produce IAA. PSB-7 produced the highest amount of IAA followed by PSB-2. Further, planta studies would be needed to confirm their efficiency as good plant growth-promoting agents.