Maize rhizosphere in Sichuan, China, hosts plant growth promoting Burkholderia cepacia with phosphate solubilizing and antifungal abilities

Plant growth-promoting rhizobacteria promote plant growth by direct and indirect mechanisms. We isolated twelve bacterial strains showing different degrees of phosphate solubilizing activity from maize rhizosphere. Four isolates solubilized over 300 μg mL−1phosphate from insoluble Ca3(PO4)2, with isolate SCAUK0330 solubilizing over 450 μg mL−1. Based on the 16S rRNA gene sequence analysis SCAUK0330 was identified as Burkholderia cepacia. SCAUK0330 grew at 10–40 °C and pH 4.0–10.0, tolerated up to 5% NaCl, and showed antagonism against nine pathogenic fungi. SCAUK0330 promoted the growth of both healthy and Helminthosporium maydis infected maize plants, indicating that the isolate was a good candidate to be applied as a biofertilizer and a biocontrol agent under a wide range of environmental conditions.The expression of a single SCAUK0330 gene gave E. coli a pH decrease linked ability to solubilize phosphate. The nucleotide and the deduced amino acid sequences of this phosphate solubilization linked gene showed high degree of sequence identity with B. cepacia E37gabY. The production of gluconic acid is considered as the principle mechanism for phosphate solubilization. In agreement with the proposed periplasmic location of the gluconic acid production, the predicted signal peptide and transmembrane regions implied that GabY is membrane bound.