Isolation, Screening and Biochemical Characterization of PhosphateSolubilizing Rhizobacteria Associated with Coffea arabica L

Abstract

This study focused on screening, identifying and characterizing P-solubilizing rhizobacteria associated with Coffea arabica L. growing in Southwestern Ethiopia. Samples were collected from Kaffa and Jimma zones in the Southwestern part of Ethiopia which are not only the major coffee growing areas of Ethiopia but also the origin of Coffea arabica L. Natural forest, agroforestry-based and monoculture plantations were included. Coffee roots with adhering soil samples were collected in sterile plastic bags. A total of 169 bacteria were isolated on nutrient agar from root washing solutions (61 isolates), surface sterilized roots (45 isolates) and soil (63 isolates). These bacteria isolates were subjected to GEN III Micro-plate tests of Biolog bacterial identification system kits and also evaluated for their ability to solubilize phosphates on Pikovskaya's agar plates. They belong to different bacterial genera: Pseudomonas, Bacillus, Enterobacter, Citrobacter, Stenotrophomonas, Gordonia, Mycobacterium, Corynibacterium and Rhodococcus. Members of the identified rhizobacteria were dominated by the genus Pseudomonas (44.1%) followed by Bacillus (11.6%), Enterobacter (10.5%) and Stenotrophomonas (10.5%). Over 32.5 % of the Rhizobacteria (both Gram-negative and Gram-positive) associated with the coffee rhizosphere were able to solubilize mineral P on Pikovskaya's agar, indicating a high proportion of such species is associated with coffee plants. The biochemical analysis in this study revealed the presence of a wide array of Gram negative and Gram positive bacteria associated with Coffee plants, but further studies should focus on the use of molecular techniques to show the complete diversity of the existing Phosphate solubilizing bacteria associated with Coffee plants. These isolates should also be evaluated and screened for bio-inoculant preparations