Heavy metal tolerant endophytic fungi Aspergillus welwitschiae improves growth, ceasing metal uptake and strengthening antioxidant system in Glycine max L

In modern agricultural practice, heavy metal (HM) contamination is one of the main abiotic stress threatening sustainable agriculture, crop productivity, and disturb natural soil microbiota. Different reclamation techniques are used to restore the contaminated site; however, they are either costly or unable to remove contaminant when concentration is very low. In such circumstances, bioremediation is used as a novel technique involving microbes for soil restoration. In the current project, Aspergillus welwitschiae(Bk) efficiently endure metal stress (i.e., Cr-VI and As-V in the form of K₂Cr₂O₇ and Na₃AsO₄) up to 1200 μg/mL and enhanced the production of phytohormones, i.e., 54.83 μg/mL of indole acetic acid (IAA) compared to control 15.56 μg/mL, solubilized inorganic phosphate, and produced stress-related metabolites. The isolate Bk was able to enhance growth of soybean by showing higher root shoot length and fresh/dry weight under stress (p<0.05). Besides, the strain strengthened the antioxidant system of the host increasing enzymatic antioxidants, i.e., catalases (CAT) by 1.58 and 1.11 fold, ascorbic acid oxidase (AAO) by 6.75 and 7.94 fold, peroxidase activity (POD) by 1.12 and 1.37 fold, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) by 1.42 and 1.25 fold at 50 μg/mL of chromate and arsenate. Thus, actively scavenging the reactive oxygen species (ROS) produced results in lower ROS accumulation and high ROS scavenging. On the other hand, the isolates cut down Cr and As uptake by approximately 50% at 50 μg/mL from the medium while bio-transforming it, thereby stabilizing it and assisting the host to resume normal growth, thus avoiding phytotoxicity. It is evident from the current study that A. welwitschiae may potentially be used as a bioremediating agent for reclamation of Cr- and As-contaminated soil.