Detoxification of Cr(VI) and extracellular formation of nanoparticles Cr2O3 by a highly Cr(VI)-resistant fungus Fusarium solani SWUZF-1

In this study, a novel highly Cr(VI)-resistant fungus Fusarium solani SWUZF-1, tolerating 10 g/L Cr (VI), was obtained from an abandoned factory of heavy metals contaminated. F. solani SWUZF-1 could effectively remove Cr(VI) under extensive environmental conditions. The removal rate of Cr (VI) reached 100% when the concentration of Cr(VI) was less than 100 mg/L. At 10 g/L Cr(VI), the removal amount of Cr(VI) still reached 1179.76 mg/L (11.80%). Chromium induced the mycelia swelling and severe ultrastructural alterations in the hypha (the thickening of the cell wall and the radius of the vesicle increasing). FTIR showed that N-H, O-H, C--O, and other functional groups on the surface of strain SWUZF-1 interacted with Cr(VI). The experiments on cell degeneration showed that Cr(VI) removal was mainly bio-reduction rather than biosorption. The cell-free suspension had the highest removal rate of Cr(VI), indicating that Cr(VI) reduction mainly occurred extracellularly. Analysis of SEM-EDX and TEM-EDX demonstrated that Cr2O3 nanoparticles were one of the reduced products of Cr(VI). Furthermore, this study compared the transcriptional changes in F. solani SWUZF-1 at 0 and 10 g/L Cr(VI) by de novo transcriptomic analysis. A total of 2352 differentially expressed genes (DEGs) were identified. These DEGs were relevant to the cell wall, apoptosis, DNA replication, hormonal regulation, transportation, reductase, etcetera. The genes related to the cell wall upregulated, indicating that the cell wall of F. solani SWUZF-1 thickened, which was also confirmed by TEM. This study revealed a fungus F. solani SWUZF-1 with the potential to remediate wastewater polluted by Cr(VI) and enlarged an insight into the Cr(VI) reduction mechanism of F. solani SWUZF-1.