Soil-borne alkaline phosphatase-producing Bacillus and Penicillium species as growth promoters of the Corchorus olitorius and Amaranthus hybridus plants

Abstract

Phosphorus; is an essential element for plant growth, which may be abundant in the soil but unavailable, because it is poorly soluble and forms complexes with the metals. Microorganisms can solubilize and mineralize the insoluble phosphate into bioavailable forms. This study aimed to isolate and identify the phosphate-solubilizing microorganisms (PSMs), produce and characterize alkaline phosphatase, and determine their plant growth promoting abilities. About forty-one bacterial and twelve fungal isolates were isolated from the soil and water samples, and then screened for their phosphate solubilizing potentials on Pikovskaya (PVK), and the National Botanical Research Institute's Phosphate (NBRIP) growth media. The isolates of Penicillium sp. (PSF-8) and Bacillus sp. (PSB-29) produced the highest alkaline phosphatase at pH 8, 42 ο C on the 2 nd and 3 rd d of incubation; and they solubilized concentrations of 937.78 and 848.89 µg/ ml of phosphates, respectively. The optimum temperature and pH activity of the alkaline phosphatase produced by Penicillium sp. (PSF-8) were recorded at 50°C (1.145 U/ ml) and pH 9 (1.147 U/ ml), respectively. On the other hand, Bacillus sp. (PSB-29) expressed maximum activity at 40°C (1.232 U/ ml) and pH 8 (1.39 U/ ml), respectively. The Michaelis constant (K m ) and maximum velocity (V max ) for Penicillium sp. (PSF-8) were 23.596 mmol/ l and 2.940 µmol/ l/ min., whereas those for Bacillus sp. (PSB-29) were 11.889 mmol/ l and 0.0894 µmol/ l/ min., respectively. Bacillus sp. (PSB-29) enhanced the growth of both Amaranthus hybridus and Corchorus olitorius ; by increasing the plant shoot and root length, biomass and phosphorus content, while Penicillium sp. (PSF-8) did not support A. hybridus growth. Finally, Bacillus sp. (PSB-29) and Penicillium sp. (PSF-8) were observed as potent bioagents for phosphate-solubilization during the farming activities.