Efficient Removal of arsenic from the environment by endophytic fungus Serendipita indica through bio-accumulation in cells and adsorption on the cell wall

Arsenic contamination is a critical environmental issue, necessitating effective and sustainable bioremediation approaches. This study investigates the arsenic tolerance and removal potential of the endophytic fungus Serendipita indica (Syn. Piriformospora indica ), which colonizes diverse plants and offers unique advantages due to its axenic cultivability. The impact of arsenic (As) stress was assessed across fungal growth phases under varying concentrations (0–375 ppm), revealing no adverse effects on biomass, spore germination, or spore numbers. The RT/RC ratio for mycelial growth was > 100 % in all treatments (up to 5 mM arsenic), while the tolerance index (TI) was observed to remain above > 1 for biomass parameters up to the 1 mM arsenic concentrations, indicating strong resilience to arsenic stress. Biochemical analysis demonstrated significant increases in antioxidative enzyme activities, including glutathione reductase (GR), glutathione-S-transferase (GST), and glutathione (GSH), under arsenic exposure as an adaptation to pacify As-induced ROS by arsenic-GSH conjugation for As detoxification and facilitated the accumulation of arsenic in fungal biomass, with huge sequestering in chlamydospores. Additionally, Zeta potential analysis demonstrated a decrease in fungal cell wall surface charge under arsenic stress, indicative of enhanced adsorption potential, and it aided to arsenic adsorption up to 2100 ppm on the cell wall. FTIR analysis revealed significant shifts in peaks corresponding to -NH group in chitin, suggesting their involvement in arsenic binding. Collectively, these mechanisms enabled the fungus to remove up to > 98 % of arsenic from the growth environment. This study provides the first detailed report on arsenic tolerance and removal mechanisms in an AMF-like endophytic fungus, positioning S. indica as a novel bioremediation agent. Its ability to thrive under high arsenic stress, coupled with efficient arsenic removal, highlights its potential for large-scale applications in mitigating arsenic pollution. • S. indica shows dose-dependent tolerance, inducing growth/biomass at low As level. • As bioavailability is reduced by accumulation in mycelia and adsorption on cell wall. • Chlamydospore can store huge As without hampering viability and germination (>95 %). • Chitin associated –N acetyl group in fungal cell wall involved in As adsorption. • S. indica can efficiently remove > 98 % of As from the growth environment.