African Journal of
Microbiology Research

  • Abbreviation: Afr. J. Microbiol. Res.
  • Language: English
  • ISSN: 1996-0808
  • DOI: 10.5897/AJMR
  • Start Year: 2007
  • Published Articles: 5233

Full Length Research Paper

Solubilization of inorganic phosphates and plant growth promotion by strains of Pseudomonas fluorescens isolated from acidic soils of Cameroon

FANKEM Henri1, NGO NKOT Laurette1, DEUBEL Annette2, QUINN John3, MERBACH Wolfgang2, ETOA François-Xavier4 and NWAGA Dieudonné5*
1Department of Plant Biology, Faculty of Science, University of Douala. P.O. Box: 24157 Douala. Cameroon. 2Institute of Soil Science and Plant Nutrition, Martin-Luther University Halle-Wittenberg, Adam-Kuckhoff-Straße 17 b, D-06108 Halle/Saale, Germany. 3Queen’s University, Belfast, School of Biology and Biochemistry, Medical Biology Centre. 97 Lisburn Road Belfast. BT9 7BL, UK. 4Department of Biochemistry, University of Yaoundé I. P.O. Box: 812 Yaoundé, Cameroon. 5Laboratory of Soil Microbiology, Biotechnology Centre, University of Yaoundé I. P.O. Box: 812 Yaoundé. Cameroon.
Email: [email protected]

  •  Accepted: 25 June 2008
  •  Published: 31 July 2008


A trial of a screening and selection strategy for phosphate-solubilizing bacteria based on phosphate solubilization ability, and the subsequent effect of these strains on plant growth promotion under in situ conditions was conducted. Of all the bacteria tested, three Pseudomonas fluorescens strains (CB501, CD511 and CE509) were selected. On agar plates, two strains (CB501 and CE509) showed an ability to solubilize the three phosphate types (Ca(PO4)2, AlPO4·H2O or FePO4·2H2O), while strain CD511 showed a halo zone only on an agar plate supplemented with iron phosphate (Fe-P). However, in liquid media, all the strains were able to mobilize significant amounts of phosphorus (P) depending on the phosphate type. Calcium phosphate (Ca-P) solubilization resulted from the combined effects of pH decrease and carboxylic acids synthesis. At pH 4, it was solubilized by most of the organic acids. However, the synthesis of carboxylic acids was the main mechanism involved in the process of aluminium phosphate (Al-P) and Fe-P solubilization. Both were mobilized at pH 4 by citrate, malate, tartrate, and on a much lower level by gluconate and trans-aconitate.Subsequently, a greenhouse trial was conducted using Zea mays, the results of which obtained using 5 parameters including grain yield and P uptake, revealed that strain CB501 was the best plant growth promotor with a global effect of +37%, followed by strain CE509 (+21.2%) and then by strain CD511 (+16.7%). However, the selection of phosphate-solubilizing Pseudomonas strains as possible inoculation tools for phosphate-deficient soils should focus on the integral interpretation of laboratory assays, greenhouse experiments and field trials.


Key words: Carboxylic acids, Phosphate solubilization, plant growth,Pseudomonas fluorescens.