Characterization of Rhizobacteria isolated from Wild Coffea arabica L.

Rhizobacteria from wild Arabica coffee Populations (Coffea arabica L.) in southwestern Ethiopia were isolated and characterized. The main purpose was to identify coffee-associated rhizobacteria and evaluate their potential in synthesizing the phytohormone indole acetic acid (IAA) and in degrading the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC). A total of 878 bacterial isolates were screened, of which 395 (45%) isolates were preliminarily characterized using metabolic identification kits (API). Both Gram-negative and Gram-positive bacteria were isolated, with the former group predominating (63% of cases). Based on pre-screening results of the biochemical tests, 51 of the isolates were subjected to PCR-RFLP (Restriction Fragment Length Polymorphism) analysis that yielded ten groups, of which 24 isolates were identified by 16S rRNA gene sequencing. The major genera identified were Pseudomonas (six species) and Bacillus (four species). Single species of Erwinia, Ochrobactrum and Serratia were also identified. The Erwinia sp., Serratia marcescens and many Pseudomonas spp. produced IAA, and some isolates (all Pseudomonas spp.) were also able to degrade ACC. Several of the microbes found in association with wild Arabica coffee bushes have potential agronomic importance, like e.g. Bacillus thuringiensis, which deserve further testing. According to these in vitro Studies, Isolates of Erwinia, Serratia and Pseudomonas are of particular interest in inoculant development due to their plant growth promoting traits.