Screening of bacterial isolates for phosphate solubilizing capability in a ferruginous ultisol in Benin City, Edo State, Nigeria

Abstract

Phosphorus is a major growth-llimiting nutrient which plays important biochemical role in living system. It is widely distributed in minerals as phosphates. It reacts easily with Fe³⁺ in ferruginous ultisols and therefore not bioavailable for plant usage. Many bacteria have the ability to solubilize phosphate minerals and make it bioavailable to plants.Thus this research investigates the culturable bacterial composition of ferruginous ultisol, comparative to control soils as well as the phosphate solubilizing capabilities of the isolates for future use in soil improvements. Six soil samples of different ferruginous levels and a control were assayed for physicochemical parameters prior to the experiment. Culturable bacteria as well as the phosphate solubilizing bacteria (PSB) were assayed in Pikovskaya’s medium at 27oC with 7.5 pH for 7days. Six distinct isolates were observed which proved to be Proteus spp., Pseudomonas spp., Klebsiella spp., Salmonella spp., Bacillus spp. and Serratia spp. based on biochemical and morphological characteristics. Of these six isolates, three isolates
(EMBF2-Klebsiella spp, BCAF1- Proteus spp and BCAC2- Bacillus spp) were identified to solubilize phosphate by releasing a considerable amount of phosphate (12.01-21.23 ppm) and lowering the pH of the media. The three isolates showed tolerance to acidic and alkaline media and also showed plant growth promoting capabilities by releasing indole acetic acid and siderophores. The result revealed that the three isolates had potential to chelate the ion bond in identified to solubilize phosphate by releasing a considerable amount of phosphate (12.01-21.23 ppm) and lowering the pH of the media. The three isolates showed tolerance to acidic and alkaline media and also showed plant growth promoting capabilities by releasing indole acetic acid and siderophores. The result revealed that the three isolates had potential to chelate the ion bond in Fe³⁺ in ferruginous ultisol by releasing low molecular weight organic acid, making phosphate to be bioavailable for plant usage. This will serve as biofertilizer in improving yield of crops in ferruginous ultisol and improve soil fertility.