| Arsenic (As) accumulation and volatilization by microorganism decreasing environmental risk of As in soil has been recognized as an economically efficient remediation method without secondary pollution. However, few fungi highly capable of As accumulation and volatilization have been identified, and the mechanisms of As accumulation and volatilization in fungi are unclear. In this study, three As resistant fungal strains were isolated and identificated from As contaminated soil samples, the abilities of As accumulation and volatilization of fungi were evaluated, and the possible mechanisms were investigated. The major findings were obtained as follows:1. Thirteen As resistant fungal strains were isolated from six soil samples. Among them, SM-12F1, SM-12F4, and CZ-8F1 performed better at As concentration of 20000, 30000, and 30000 mg·L-1 respectively. When incubated in liquid medium containing the As (V) concentration of 50, 80, 50 mg·L-1 for 2 days, the biomass for SM-12F1, SM-12F4, CZ-8F1 were significantly increased compared to CK, and the sporalation of SM-12F1, SM-12F4, CZ-8F1 was not affected by addition of As (V). Scanning Electron Microscope (SEM) analysis suggested that little impact on mycelium growth of the three fungal strains was found, the fungi SM-12F1, SM-12F4, CZ-8F1 showed higher ability of As resistance.2. The colony morphology, spore structure of SM-12F1, SM-12F4, and CZ-8F1 were respectively similar to those of Trichoderma asperellum, Penicillium janthinellum, and Fusarium oxysporum. Phylogenetic tree based on comparative analysis of 18S rRNA sequence data from the three isolates and their relatives indicated that SM-12F1, SM-12F4, and CZ-8F1 were homology with T. asperellum, P. janthinellum, and F. oxysporum, respectively, with 99%, 96%, and 99% of the similarity. Online sequences comparison to GenBank obtained accession number as follow: GU212867, GU212865, and GU212866.3. T. asperellum SM-12F1, P. janthinellum SM-12F4, and F. oxysporum CZ-8F1 were all capable of As accumulation and volatilization, the highest level of As was accumulated by P. janthinellum SM-12F4, with 39.54μg after 10 days in the culture system amended with 50 mg·L-1 As (V). F. oxysporum CZ-8F1 showed the highest amount of volatilized As, with 304.06μg after 15 days. T. asperellum SM-12F1 and F. oxysporum CZ-8F1 showed greater abilities for the absorption of extracellular As and the accumulation of intracellular As, which accounted for 82.2% and 63.4% of the total accumulated As, respectively. However, P. janthinellum SM-12F4 presented an approximately equipotent distribution of intracellular and extracellular As. The As content in the treated system (filter paper + arsenic + fungi) was significantly higher than that in the control (filter paper + arsenic; filter paper + fungi; filter paper), the abilities of As volatilization by three fungal strains were further certified.4. After cultivated for 2-3 days, As (V) was totally transferred into As (III) in medium of T. asperellum SM-12F1, P. janthinellum SM-12F4, and F. oxysporum CZ-8F1. During the whole cultivation period, As (V) was predominant in cells of three fungal strains, and after cultivated for 15 days, As (III), MMA (Monomethylarsonite), and DMA (Dimethylarsinite) were found in cells of T. asperellum SM-12F1. The change in pH and Eh in medium of three fungal strains showed that the transformation of As (V) into As (III) was conducted in fungal cells. After cultivated for 7 days, the pH in cultural medium of T. asperellum SM-12F1, F. oxysporum CZ-8F1, and P. janthinellum SM-12F1 was 6.69, 8.38, and 3.78 respectively. The adsorption of inorganic As on the cellular wall might be improved in the acidic culture environment.
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