FONSECA Maria Isabel
congresos y reuniones científicas
Simposio; LVI SAIB Meeting ? XV SAMIGE Meeting; 2020
Chromium (VI) is one of the most common environmental contaminants. Mycoremediation is an interesting option to remove pollutants in soil because fungi are considered the most suitable candidates due to their high tolerance to heavy metals. Metal tolerance is one of the properties evaluated when searching microorganisms for bioremediation processes. The current study was aimed to isolate, identify, and test the tolerance of indigenous fungal strains from chromium contaminated soil. Soil used was collected around an effluent treatment plant from tannery industry. Soil samples were serially diluted from 10−1 to 10−10 and 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 and morphological characteristics. Fungal strain tolerance towards Cr was analyzed in 90 mm diameter agar plates containing Lee minimum medium supplemented with 500 and 800 mgL−1 of K2Cr2O7. Inoculum consisted of a 5 mm diameter agar plug taken from a 5?7-day-old fungal colony. Incubation was carried out at 28°C in darkness. Growth was followed by daily measuring the radial extension of the mycelium until the complete coverage of the plates. Fungal growth was modelled by using 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 fungal growth 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 control culture without the pollutant, respectively. A positive value of Δτ proved fungal growth inhibition in response to Cr. A total of 13 fungal strains were isolated and identified within three genera: Trichoderma (four strains), Aspergillus (four strains) and Penicillium (five strains). It was possible to group the strains according to their tolerance and growth velocity. Four fungal strains of Trichoderma and Penicillium genus showed Δτ < 2. Three strains of Aspergillus and Penicillium genus displayed a Δτ between 4 and 10. Finally, two strains of Aspergillus and Trichoderma genus revealed Δτ > 10 representing the group of fungi more severely affected by the presence of Cr. Effective bioremediation requires the selection of microorganisms with high tolerance and high growth rate in presence of pollutant; thereby, from the obtained results, a Trichoderma genus strain could be ranked as a promising chromium remediator because it showed Δτ < 1 in both tested concentrations which means low inhibition and high growth rate.