The tannery industry releases important amounts of chromium into the environment, its hexavalent form being highly toxic to all forms of life. The soil microbiota is an important component of terrestrial ecosystems because it influences the services and overall functioning of the soil [1]. Numerous fungal genera are able to survive in heavy-metal- contaminated environments, and even to reduce their concentration or to metabolize them to less toxic forms, through various resistance mechanisms [2]. For this reason, biological soil remediation methods are taken into consideration for their low costs, low negative impact on the environment as well as their role in ecological restoration [3]. The aim of the present study was to isolate heavy-metal-resistant filamentous fungi from chromium- contaminated soil to be applied in bioremediation.
Soil samples were collected from the surface layer in February 2023 from the proximity of a leather processing unit located in Bucharest. Physicochemical characterization, moisture and organic matter were determined by the loss on ignition method, and pH was analyzed using a glass electrode of hydrogen. Total chromium content was determined by ICP-MS. Several filamentous fungi were isolated on agar media supplemented with chloramphenicol and K2Cr2O7. The tolerance index was assayed on agar media containing concentrations of chromium in a range of 50 to 1000 mg L−1. Growth diameters were measured daily for 7 days, and the ratio between sample and control was compared. Values of the tolerance index between 0.80–0.99 indicated a high tolerance, and values equal or above to 1 indicated a very high tolerance [4]. Micro- and macroscopical observations were performed to identify any morphological modifications determined by interactions between the fungal strains and chromium.
Following physicochemical characterization, the soil proved to be low in moisture and organic matter, with a slightly alkaline pH. A number of 20 fungal strains were isolated, displaying various levels of tolerance to the concentrations of chromium tested. Most of the resistant strains were determined to belong to the Trichoderma sp. genera. Low concentrations of chromium proved to stimulate growth in a small number of strains, whereas in others it produced macroscopic and microscopic changes represented by increased production of pigment and delayed sporulation.
Through our study, we have successfully isolated filamentous fungi that displayed various degrees of resistance to chromium. Further studies will be focused on analyzing the ability of the highly tolerant fungal strains to reduce the concentration of chromium in soil solution.
Author Contributions
C.F., I.R., M.-L.J., L.C., R.R.C., A.-M.G., L.-G.Z., M.D., L.J., M.C., C.P., T.E.Ș. contributed equally to this paper. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the Ministry of Research, Innovation and Digitization through Core Program PN23.06.01.01.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Acknowledgments
The authors thank the Ministry of Research, Innovation and Digitalization through Program 1—Development of the national research and development system, Subprogram 1.2—Institutional performance—Projects to finance excellence in RDI, Contract no. 15PFE/2021.
Conflicts of Interest
The authors declare no conflict of interest.
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