Isolation of heavy metal-resistant fungi from contaminated soil and co-culturing with rice seedlings

Environmental pollution from toxic heavy metals is a growing problem throughout the world due to the expansion of industrialisation. The use of microbes and biotechnological processes can provide alternative or complementary methods for the removal or recovery of heavy metals through bioremediation. The present study isolated, identified and characterised heavy metal-resistant fungi from cadmium- and chromium-contaminated paddy soil from Daye City, Hubei Province, China. Eight metal-resistant fungal species were obtained using an acclimation to concentration gradient approach. Five strains tolerated cadmium (Cd2+) to a maximum concentration of 16 mM, four strains could endure 1000 mg/L chromium (Cr2+), and Fusarium oxysporum could withstand high levels of both metals. Morphological examination and 18S rDNA sequence analysis identified the strains. Metal-resistant fungi were co-cultured with 5-day-old rice (Oryza sativa) seedlings in 1/2 MS medium for 7 days and growth parameters were compared with control rice not incubated with microbes. In the obtained strains, Metarhizium anisopliae had no influence on plant height or root length, and Saccharomyces cerevisiae had no effect on these parameters or on fresh weight. Heavy metal-resistant fungi such as those identified in this study could prove useful for the bioremediation of heavy metal-contaminated environments.