Autochthonous strains of Trichoderma isolated from tannery solid waste improve phytoextraction potential of heavy metals by sunflower

Trichoderma Inoculation Alleviates Cd and Pb-Induced Toxicity and Improves Growth and Physiology of Vigna radiata (L.)

Heavy metals (HMs) pose a serious threat to agricultural productivity. Therefore, there is a need to find sustainable approaches to combat HM stressors in agriculture. In this study, we isolated Trichoderma sp. TF-13 from metal-polluted rhizospheric soil, which has the ability to resist 1600 and 1200 μg mL-1 cadmium (Cd) and lead (Pb), respectively. Owing to its remarkable metal tolerance, this fungal strain was applied for bioremediation of HMs in Vigna radiata (L.). Strain TF-13 produced siderophore, salicylic acid (SA; 43.4 μg mL-1) and 2,3-DHBA (21.0 μg mL-1), indole-3-acetic acid, ammonia, and ACC deaminase under HM stressed conditions. Increasing concentrations of tested HM ions caused severe reduction in overall growth of plants; however, Trichoderma sp. TF-13 inoculation significantly (p ≤ 0.05) increased the growth and physiological traits of HM-treated V. radiata. Interestingly, Trichoderma sp. TF-13 improved germination rate (10%), root length (26%), root biomass (32%), and vigor index (12%) of V. radiata grown under 25 μg Cd kg-1 soil. Additionally, Trichoderma inoculation showed a significant (p ≤ 0.05) increase in total chlorophyll, chl a, chl b, carotenoid content, root nitrogen (N), and root phosphorus (P) of 100 μg Cd kg-1 soil-treated plants over uninoculated treatment. Furthermore, enzymatic and nonenzymatic antioxidant activities of Trichoderma inoculated in metal-treated plants were improved. For instance, strain TF-13 increased proline (37%), lipid peroxidation (56%), catalase (35%), peroxidase (42%), superoxide dismutase (27%), and glutathione reductase (39%) activities in 100 μg Pb kg-1 soil-treated plants. The uptake of Pb and Cd in root/shoot tissues was decreased by 34/39 and 47/38% in fungal-inoculated and 25 μg kg-1 soil-treated plants. Thus, this study demonstrates that stabilizing metal mobility in the rhizosphere through Trichoderma inoculation significantly reduced the detrimental effects of Cd and Pb toxicity in V. radiata and also enhanced development under HM stress conditions.

Screening of Native Trichoderma Species for Nickel and Copper Bioremediation Potential Determined by FTIR and XRF

Soil pollution with heavy metals is a serious threat to the environment. However, soils polluted with heavy metals are considered good sources of native metal-resistant Trichoderma strains. Trichoderma spp. are free-living fungi commonly isolated from different ecosystems, establishing endophytic associations with plants. They have important ecological and biotechnological roles due to their production of a wide range of secondary metabolites, thus regulating plant growth and development or inducing resistance to plant pathogens. In this work we used indigenous Trichoderma strains that were previously isolated from different soil types to determine their tolerance to increased copper and nickel concentrations as well as mechanisms of metal removal. The concentrations of bioavailable metal concentrations were determined after extraction with diethylene-triamine pentaacetate (DTPA)-extractable metals (Cd, Cr, Co, Cu, Pb, Mn, Ni, and Zn) from the soil samples by inductively coupled plasma-optical emission spectrometry (ICP-OES). Two indigenous T. harzianum strains were selected for copper tolerance, and three indigenous T. longibrachiatum strains were selected for nickel tolerance tests. Strains were isolated from the soils with the highest and among the lowest DTPA-extractable metal concentrations to determine whether the adaptation to different concentrations of metals affects the mechanisms of remediation. Mechanisms of metal removal were determined using Fourier-transform infrared spectroscopy (FTIR) and X-ray fluorescence spectroscopy (XRF), non-destructive methods characterized by high measurement speed with little or no need for sample preparation and very low costs. Increased DTPA-extractable metal content for nickel and copper was detected in the soil samples above the target value (TV), and for nickel above the soil remediation intervention values (SRIVs), for total metal concentrations which were previously determined. The SRIV is a threshold of metal concentrations indicating a serious soil contamination, thus confirming the need for soil remediation. The use of FTIR and XRF methods revealed that the presence of both biosorption and accumulation of metals in the Trichoderma cells, providing good bioremediation potential for Ni and Cu.