Transcriptomic responses of catalase, peroxidase and laccase encoding genes and enzymatic activities of oil spill inhabiting rhizospheric fungal strains

Highlights: • New four dominant fungal strains were identified from rhizospheres in oil-spill site. • They were able to tolerate up till 20% crude oil concentration. • They showed presence and expression of lig, mnp, lcc and cbh genes. • They produced up till 145 U/ml peroxidases, 87 U/ml catalase, and 180 U/ml laccase. 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.