Ureolytic activity and growth criteria of some soil fungi affected by various concentrations of urea

ABSTRACT

It was found that there is no regular relation between the density of fungi isolated from soil amended with urea and their ureolytic activity. For instance, Aspergillus fumigatus constituted the highest density and ureolytic activity but Fusarium nivale was of low density and high ureolytic activity. Oppositely, high density but showed weak ureolytic activity. The effect of various urea concentrations added to culture medium as sole N-source showed that the ED50 was 8.5 percent urea in Aspergillus fumigatus, 6.5 percent in A niger, A. Flavus and Paecilomyces silvaticaA.5 percent in Pencillium notatum and 2.5 percent in Humicola grisea and Sepedonium chrysospermum. No detectable ED50 was observed in F. nivale .The concentration 10.5 percent was lethal for the eight tested fungi. Regarding the growth parameters, the spore germination, linear growth rate and dry biomass in all tested fungi decreased significantly with the increase in urea concentrations except in F .nivale where an increase in these growth criteria was recorded up to 4.5 percent urea. The pH value of the culture medium at the end of the incubation period shifted to alkaline side in A. fumigatus, A. niger and A .Flavus while no noticeable change was recorded in the media of the other fungi