CONICET | Buscador de Institutos y Recursos Humanos

Chromium (VI) is one of the most common environmental contaminants. Mycoremediation is an interesting option to removepollutants in soil because fungi are considered the most suitable candidates due to their high tolerance to heavy metals. Metaltolerance is one of the properties evaluated when searching microorganisms for bioremediation processes. The current studywas aimed to isolate, identify, and test the tolerance of indigenous fungal strains from chromium contaminated soil. Soil usedwas collected around an effluent treatment plant from tannery industry. Soil samples were serially diluted from 10−1 to 10−10and fungi were isolated by pour plate technique on Lee minimum medium. After obtaining a pure culture of the fungal isolates,macroscopic and microscopic examination of pure isolates was carried out. The characterization was based on colonial andmorphological characteristics. Fungal strain tolerance towards Cr was analyzed in 90 mm diameter agar plates containing Leeminimum medium supplemented with 500 and 800 mgL−1 of K2Cr2O7. Inoculum consisted of a 5 mm diameter agar plugtaken from a 5?7-day-old fungal colony. Incubation was carried out at 28°C in darkness. Growth was followed by dailymeasuring the radial extension of the mycelium until the complete coverage of the plates. Fungal growth was modelled byusing a logistic equation, D = Dmáx / 1 + ek(T − t), where D was the diameter of the fungal colony or the diameter of the halo,with Dmax being the maximum diameter (set to 8.5 cm, corresponding to the diameter of the plates); k was the rate of fungalgrowth or the rate of enzyme activity on plate (cm/day); τ was the time needed to attain half of Dmax (days), and t was the time(days). Fitting was performed through the software InfoStat 2016p using a least-squares approach with nonlinear regression.τ was standardised as Δτ = τCr ? τC, where τCr and τC were the values from medium supplemented with K2Cr2O7 and controlculture without the pollutant, respectively. A positive value of Δτ proved fungal growth inhibition in response to Cr. A totalof 13 fungal strains were isolated and identified within three genera: Trichoderma (four strains), Aspergillus (four strains) andPenicillium (five strains). It was possible to group the strains according to their tolerance and growth velocity. Four fungalstrains of Trichoderma and Penicillium genus showed Δτ < 2. Three strains of Aspergillus and Penicillium genus displayed aΔτ between 4 and 10. Finally, two strains of Aspergillus and Trichoderma genus revealed Δτ > 10 representing the group offungi more severely affected by the presence of Cr. Effective bioremediation requires the selection of microorganisms withhigh tolerance and high growth rate in presence of pollutant; thereby, from the obtained results, a Trichoderma genus straincould be ranked as a promising chromium remediator because it showed Δτ < 1 in both tested concentrations which meanslow inhibition and high growth rate.

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