Fungi are well associated with the degradation of hydrocarbons by the production of different enzymes, among which catalases (CBH), laccases (LCC) and peroxidases (LiP and MnP) are of immense importance. In this study, crude oil tolerance and enzyme secretions were demonstrated by rhizospheric fungal strains. Four most abundant strains were isolated from the rhizosphere of grasses growing in aged oil spill sites and identified through morphological characterization and molecular PCR-amplification of 5.8–28S ribosomal rRNA using ITS1 and ITS4 primers. These strains were subjected to crude oil tolerance test at 0–20% concentrations. Presence and transcriptase responses of putative genes lig (1–6), mnp, cbh (1.1, 1.1 and 11), and lcc encoding lignin peroxidase, manganese peroxidase, catalase, and laccase enzymes respectively were also studied in these strains using RT-PCR. In addition, activities of secreted enzymes by each strain were studied in aliquots. The strains were identified as Aspergillus niger asemoA (KY473958), Talaromyces purpurogenus asemoF (KY488463), Trichoderma harzianum asemoJ (KY488466), and Aspergillus flavus asemoM (KY488467) through sequencing and comparing the sequences’ data at NCBI BLAST search software. All the isolated strains showed tolerance to crude oil at 20% concentration, but the growth rate reduced with increasing in oil concentrations. All the isolated strains possess the tested genes and lig 1–6 gene was overexpressed in A. niger and T. harzianum while lcc and mnp genes were moderately expressed in all the four strains. Almost 145 U.mL⁻¹ of lignin and manganese peroxidase, 87 U.mL⁻¹ of catalase, and 180 U.mL⁻¹ of laccase enzymes were produced by these strains and it was also observed that these strain mostly produced studied enzymes in response to increasing crude oil concentrations. Considering the robust nature and diverse production of these catalytic enzymes by these strains, they can be exploited for various bioremediation technologies as well as other biotechnological applications.

Phosphate-solubilizing fungi (PSF) can secrete large amounts of organic acids. In this study, the application of the fungus Penicillium oxalicum and geological fluorapatite (FAp) to lead immobilization was investigated. The formation and morphology of the lead-related minerals were analyzed by ATR-IR, XRD, Raman, and SEM. The quantity of organic acids secreted by P. oxalicum reached the maximum on the fourth day, which elevated soluble P concentrations from 0.4 to 108 mg/L in water. The secreted oxalic acid dominates the acidity in solution. P. oxalicum can survive in the solution with Pb concentration of ~ 1700 mg/L. In addition, it was shown that ~ 98% lead cations were removed while the fungus was cultured with Pb (~ 1700 mg/L) and FAp. The mechanism is that the released P from FAp (enhanced by organic acids) can react with Pb²⁺ to form the stable pyromorphite mineral [Pb₅(PO₄)₃F]. The precipitation of lead oxalate also contributes to Pb immobilization. However, lead oxalate is more soluble due to its relatively high solubility. P. oxalicum has a higher rate of organic acid secretion compared with other typical PSF, e.g., Aspergillus niger. This study sheds light on bright future of applying P. oxalicum in Pb remediation.

Sorption is the most effective approach to the treatment of acid mine drainage (AMD) and wastewaters, but the removal of the adsorbents from water has always been a challenging problem which may be resolved by using magnetic separation. In this work, a magnetic bioadsorbent was prepared using low cost and high-performance sources and applied in Cr(VI) removal from a synthetic solution. Initially, magnetite nanoparticles were synthesized from iron boring scraps by chemical co-precipitation method. Results of dynamic light scattering (DLS) and vibrating sample magnetometry (VSM) analyses showed that the synthesized nanoparticles were around 40 nm in size and had a significant magnetization. Then, the magnetite nanoparticles were attached to the dead and alkaline activated biomass of Aspergillus niger. Central composite design (CCD) was applied to determine the optimal condition of Cr(VI) adsorption on the produced magnetic nanobiocomposite. The maximum chromium removal (~ 92%) was achieved at pH 5.8, Cr concentration 23.4 mg/l, adsorbent dose 3.72 g/l, agitation rate 300 rpm, and duration 11 min. Kinetic studies showed that regardless of temperature, the process was controlled by mass transfer and intraparticle diffusion with an equilibrium constant of 0.74 mg/g min¹/² at 40 °C. Also, the adsorption isotherms followed the Temkin model, which indicated the physical adsorption of Cr(VI) on the produced sorbent. Therefore, the magnetic nanobiocomposite has a perfect ability to be used as the chromium adsorbent and can be collected by a low external magnetic field. Graphical abstract Synthesis of the magnetic nanobiosorbent and its application in the removal of Cr(VI) from wastewaters.