Biosorption, bioaccumulation and bioreduction of hexavalent chromium by Trichoderma koningiopsis LBM 253

TATARIN, ANA SILVIA; SADAÑOSKI, MARCELA ALEJANDRA; POLTI, MARTA ALEJANDRA; FONSECA, MARÍA ISABEL

Congreso; LIX Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology Research (SAIB); 2023

Chromium (Cr) is one of the most toxic metals that cause the pollution of soil and groundwater. Cr(III) and Cr(VI) are the most stable forms of this metal. The high toxicity of Cr(VI) poses a significant threat to human health due to its potent oxidizing, mutagenic, and carcinogenic properties. Mycoremediation is an eco-friendly and effective technology to clean Cr contaminated sites. Fungal exposure to heavy metals can induce the development of mechanisms that allow them to metabolize and reduce the concentration of these pollutants through mostly involving biosorption, bioaccumulation and/or bioreduction. Based on this background, the aim of this work was to determine the main mechanisms implicated in Cr mycoremediation. Biosorption, bioaccumulation and bioreduction assays were carried out with 4, 8, and 12 days of fresh fungal mycelia cultured in presence of 200 mg L-1 of Cr(VI). Controls were carried out with fungal mycelia cultured without Cr(VI). Mycelia were fixed, dehydrated, dried, and gold metalized to analyze using a scanning electron microscope coupled with an energy-dispersive X-ray spectrophotometer (SEM-EDX) to biosorption assays. Fresh mycelia were disrupted with liquid nitrogen, and the supernatant was used for Cr(VI) bioaccumulation and intracellular chromate reductase (ChrR) activity determinations. Metal bioaccumulation capacity was calculated based on Cr(VI) intracellular concentration. SEM-EDX analysis confirmed biosorption mechanism through the presence of Cr on the mycelial surface of T. koningiopsis LBM 253. EDX analysis did not detect Cr on fungal surfaces from the control assays. The determination of Cr(VI) bioaccumulation revealed values of 3.47 ± 0.28; 4.82 ± 0.14 and 6.63 ± 0.45 µg g-1 at 4, 8, and 12 days of incubation, respectively. These results demonstrate that T. koningiopsis LBM 253 was able to bioaccumulate Cr(VI) inside the cell which could be attributed to the high level of tolerance of this fungus. T. koningiopsis LBM 253 showed both extracellular and intracellular ChrR activity indicating their involvement in Cr(VI) bioreduction. Cr(VI) presence in culture media induced changes in both intracellular and extracellular ChrR activity. Notably, higher titers of extracellular ChrR activity were observed in absence of Cr(VI), and the peak of ChrR activity was detected at 4 d of incubation. In the presence of Cr(VI), the highest extracellular ChrR titers were detected at 4 and 12 d of incubation. Intracellular fractions of culture medium containing Cr(VI) exhibited the highest titers of ChrR activity at 8 d of incubation. Based on our findings, we propose that T. koningiopsis LBM 253 utilizes biosorption, bioaccumulation, as well as extracellular and intracellular bioreduction, which occur simultaneously and dynamically, enhancing the overall remediation process. This response highlights the ability of T. koningiopsis LBM 253 to remove Cr(VI) by employing different intracellular and extracellular response mechanisms.