Enhancement of phytoremediation of Cd- and Pb-contaminated soils by self-fusion of protoplasts from endophytic fungus Mucor sp. CBRF59

The aim of this study was to isolate protoplasts from endophytic fungi and to carry out self-fusion of protoplasts for their enhancement of metal resistance. Self-fusant CBRF59T3 with resistance to 25 mM Cd(II) was constructed by self-fusion of inactivated protoplasts from Mucor sp. CBRF59. The inoculation of CBRF59 and CBRF59T3 improved significantly the availability of Cd(II) and Pb(II) in the soil. Compared with CBRF59, CBRF59T3 inoculation increased the content of water-soluble Cd(II) by 24%. The dry weight of rape inoculated with CBRF59 and CBRF59T3 was both higher than that of the uninoculation rape. Inoculation of CBRF59T3 further increased the dry weight of rape by 62% than CBRF59 in the higher Cd(II)- + Pb(II)-contaminated soil. Compared with CBRF59, CBRF59T3 inoculation increased the concentration of Cd(II) in rape shoots by 35–189% in Cd(II)- and Cd(II)- + Pb(II)-contaminated soils. The inoculation of CBRF59T3 also enhanced the translocation of Cd(II) from roots to shoots and increased the amount of extracted Cd(II) by rape. The results indicated that the mutants constructed by protoplast fusion is a feasible and efficient method to improve stress tolerance of uncharacterized fungi for phytoremediation of soils contaminated by heavy metals.

Effect of CBRF59 and the self-fusant CBRF59T3 on the extraction amount of Cd in rape shoots. Different small letters on the bars indicate that the multiple comparison differences are significant with different fungi treatments and the same soils (P < 0.05). The vertical line on each bar shows the standard deviation (n = 3). CK represents the control soil without additional metals; Cd25, Cd50, Cd25 + Pb500, and Cd50 + Pb1000 represent soil samples supplemented with 25, 50 mg kg−1 of Cd(II), 25 mg kg−1 of Cd(II) and 500 mg kg−1 of Pb(II), 50 mg kg−1 of Cd(II) and 1000 mg kg−1 of Pb(II), respectively.Figure optionsDownload as PowerPoint slideHighlights
► The fusant T3 was constructed by self-fusion of protoplasts from Mucor sp. CBRF59.
► The highest Cd concentration tolerated by T3 is 4-folds higher than that of CBRF59.
► The fusant T3 improved the concentration of Cd in rape shoots compared to CBRF59.
► The fusant T3 improved the translocation factor of Cd in rape compared to CBRF59.
► The fusant T3 increased the extraction amounts of Cd by rape compared with CBRF59.