Enhancement of lead (Pb) biosorption by Gamma irradiated Aspergillus japonicus

Abstract

Among the different types of microorganisms; the fungal biomass is considered as an effective mediator for bioremediation of heavy metals, due to its higher surface area and extensive hyphal density in the soil. About seven fungal spp. were isolated from the soil garden of the Middle Eastern Regional Radioisotope Center for Arab Countries (MERRCAC); however, a single isolate of Aspergillus japonicus with high potential of metals biosorption was selected for further research during this work. Soil analysis revealed that lead concentration was 5.25 mg/ l. The aims of the present study were to gamma irradiate A. japonicus with low doses of 50 to 250Gy, in order to enhance its heavy metal tolerance ability, and to increase its efficacy for removal of lead (Pb) from the soil. Results indicated that combined treatments of A. japonicus with lead and gamma irradiation doses displayed more enhancements of its biosorption capacity and gain in dry biomass than single treatment. Treatment with Pb (1950 mg/ l) in combination with gamma irradiation (100 Gy) proved to be optimum for increasing the biosorption capacity of this isolate. However, Pb at 650 mg/ l combined with gamma irradiation at 100 Gy was the optimum for gain in dry biomass. Fourier Transform Infrared Spectroscopic (FTIR) analysis showed that the fungal biomass includes in its surface hydroxyl, carboxyl and amine groups. On the other hand, Transmission electron microscope (TEM) examination of the irradiated A. japonicus cells demonstrated accumulation of electron dense Pb on the cell wall and within the fungal cells, this indicate that Pb 2+ accumulation by fungi occurs by two methods absorption inside the cell and adsorption on the cell wall. The current study expressed a potential new method for enhancing microbial biosorption using low doses of gamma radiation.