Effect of heavy-metal stress on fungal growth and pH of fermentation broth

Abstract:

[Background] Soil heavy metal pollution is serious in the slag heap of mining area. There are some microorganisms in the slag heap of mining area that are resistant to heavy metals. [Objective] To investigate the effects of heavy metal stress on the growth of fungi and pH of fermentation broth. [Methods] The acid-producing ability of two fungi (Aspergillus niger ZJ-I, Penicilium chrysogenum ZJ-V) isolated from the slag heap of mining area as materials and their tolerance to different heavy metal ions Pb2+, Cd2+ and Zn2+ were studied by using traditional microbial culture method. [Results] The results showed that these two strains ZJ-I and ZJ-V were Aspergillus niger and Penicillium chrysogenum respectively by morphological and 18S rRNA gene sequence analysis. When the metal culture was not increased, the pH of the fermentation broth of the above two strains decreased by 0.58 and 0.69, respectively, compared with the control without inoculation of fungi and when the two strains were under heavy metal tolerance, the pH range decreased with the increase of heavy metal concentration, pH of the fermentation broth with different concentrations of Pb2+ decreased by 0.53, 0.39, 0.34 and 0.39 respectively, and by 0.21, 0.23, 0.14 and 0.09 respectively to P. chrysogenum ZJ-V. The pH of the fermentation broth with different concentrations of Cd2+ was decreased by 0.75, 0.43, 0.39 and 0.32 respectively on A. niger ZJ-I and 0.62, 0.46, 0.38 and 0.49 respectively on P. chrysogenum ZJ-V. The pH of the fermentation broth with different concentrations of Zn2+ decreased by 0.87, 0.61, 0.57 and 0.43 respectively, by 1.1, 0.34, 0.44 and 0.49 respectively to P. chrysogenum ZJ-V. The low concentration of Zn2+ promoted the acid production of A. niger ZJ-I and P. Chrysogenum ZJ-V, and the low concentration of Cd2+ promoted the acid production of A. niger ZJ-I. When the concentration of heavy metal ions Cd2+, Zn2+ and Pb2+ was more than 200, 400, 2 000 mg/L respectively, A. niger ZJ-I had significant inhibition rate reached 80%, when the concentration of heavy metal ions Cd2+, Zn2+ and Pb2+ was more than 200, 1 000, 2 000 mg/L respectively, P. chrysogenum ZJ-V had significant inhibition rate reached 80%, [Conclusion] Both fungi have acid production ability and heavy metal tolerance, strain P. chrysogenum ZJ-V is superior to A. niger ZJ-I in acid production and heavy metal tolerance, so strain P. chrysogenum ZJ-V can be used as the dominant strain for bioremediation of heavy metal contaminated soil.