Assessment of Potent Phosphate-Solubilizing Bacteria Isolated from the Olive Tree Rhizosphere Grown on Phosphate Sludge and Their Effect on Common Bean Growth

Abstract

One of the most restricting macronutrients for crop yield worldwide is phosphorus, which is often less than 1% of the total amount contained in soils. To promote its bioavailability, there are microorganisms considered vital that can solubilize and mineralize their pools in soils. In the current study, we assessed the potential of phosphate-solubilizing bacteria (PSB), isolated from the olive tree rhizosphere grown on phosphate sludge, to solubilize phosphate, promote plant growth, and tolerate abiotic stresses. Based on 16S rRNA gene sequencing, twenty-four PSB strains were identified and retained for in vitro analysis. According to the results, all the strains were able to solubilize the Moroccan rock phosphate, with soluble phosphate concentrations ranged from 5.34 µg/mL to 227 µg/mL. Furthermore, the majority of the strains are thermo-tolerant and halotolerant. Nonetheless, only five strains produced indole acetic acid. Regarding biocontrol potentialities, several PSB strains were characterized by producing hydrogen cyanide and hydrolytic enzymes (cellulase, and chitinase), of which three strains identified as Pseudomonas moraviensis, Bacillus cereus, and Bacillus aryabhattai, with a remarkable multi-trait combination were selected for antagonism and co-inoculation tests. The findings revealed that these PSB strains significantly inhibited Fusarium oxysporum (17.65%–62.35%) and Verticillium dahliae (52.35%–66.87%) and promoted common bean growth. The consortium of the three strains showed the best results by significantly increasing both plant height and tap root length and dry biomass compared to individual inoculation. The PSB selected from the olive tree rhizosphere growing on phosphate sludge have the potential to be useful as biofertilizer and biocontrol agents for attaining sustainable food crop production.

Keywords:

• 16S rRNA gene sequencing
• phosphate solubilization
• multi-trait PSB
• indole acetic acid
• Thermo-tolerance and halotolerance
• Co-inoculation

Acknowledgments

The Authors would like to acknowledge the support through the R&D Initiative – Appel à projets autour des phosphates APPHOS – sponsored by the Office Chérifien des Phosphates (OCP) (OCP Foundation, R&D OCP, Mohammed VI Polytechnic University, National Center of Scientific and Technical Research CNRST, Ministry of Higher Education, Scientific Research and Innovation of Morocco) under the project entitled ‘Procédés biotechnologiques pour la valorisation des boues et des déchets miniers de phosphate: Formulation d’un phospho-compost bio-fertilisant pour application directe en agriculture productive et respectueuse de l’environnement’ (Ref. BIO-MOD-01/2017).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was funded by the Office Chérifien des Phosphates (OCP) (OCP Foundation, R&D OCP, Mohammed VI Polytechnic University, National Center of Scientific and Technical Research CNRST, Ministry of Higher Education, Scientific Research and Innovation of Morocco) [Project. BIO-MOD-01/2017].