Isolation and characterization of culturable bacteria from bulk soil samples and the rhizosphere of arid-adapted <i>Tylosema esculentum</i> (Burchell). <i>A. Schreiber</i> (Marama bean) in Namibia

Abstract

Plant growth promoting (PGP) bacteria are microorganisms living in association with plants. PGP bacteria have various physiological activities that they perform which are beneficial to plants. For example, phosphate solubilisation, nitrogen fixation, phytostimulation and formation of siderophores. The aim of this investigation was to determine the diversity of PGP bacteria and to characterise them for possible promotion of plant growth from the rhizosphere of Tylosema esculentum, a nutritious arid adapted legume. For that purpose, in this study, bacteria were isolated from marama bean rhizosphere and bulk soil. The bacteria were screened for their ability to solubilise phosphates, for aminocyclopropane-1-carboxylate (ACC) deaminase activity, production of catalase, hydrogen cyanide, ammonia and protease activity. Efficiency of phosphate solubilising activity by bacteria was determined by phosphate solubilisation index. DNA was extracted from bacterial cultures and used to obtain 16S rDNA amplicons for bacterial molecular identification. A total of eight bacterial strains were isolated from the rhizosphere and 19 strains from bulk soil with potential plant growth promoting traits. The 27 bacterial isolates showed phosphate solubilising activity and five of the isolates had a solubilisation index of at least 6. A total of 23 isolates showed ACC deaminase activity. Hydrogen cyanide was produced by 16 isolates; 26 isolates had catalase activity, 23 isolates showed protease activity and all the isolates produced ammonia. The identified genera include Bacillus, Raoultella, Klebsiella, Acinetobacter, Arthrobacter, Kosakonia and Burkholderia. From this study, we conclude that there is a community of bacteria living in T. esculentum rhizosphere and proposed that in future these native bacterial strains can be used as biofertilisers for this arid agro-ecological area after verifying their suitability for inoculum development.

 Key words: Rhizobacteria, plant growth promoting bacteria, Kosakonia, Burkholderia.

Abbreviation: PGP, Plant growth promoting.