Cr(VI) Reduction and Fe(II) Regeneration by Penicillium oxalicum SL2-Enhanced Nanoscale Zero-Valent Iron

Abstract

Nanoscale zero-valent iron (nZVI) faces significant challenges in Cr­(VI) remediation through aggregation and passivation. This study identified a Cr­(VI)-resistant filamentous fungus (Penicillium oxalicum SL2) for nZVI activation and elucidated the synergistic mechanism in chromium remediation. P. oxalicum SL2 and nZVI synergistically and effectively removed Cr­(VI), mainly by extracellular nonenzymatic reduction (89.1%). P. oxalicum SL2 exhibited marked iron precipitate solubilization and Fe­(II) regeneration capabilities. The existence of the Fe­(II)–Cr­(V)-oxalate complex (HCrFeC4O9) indicated that in addition to directly reducing Cr­(VI), iron ions generated by nZVI stimulated Cr­(VI) reduction by organic acids secreted by P. oxalicum SL2. RNA sequencing and bioinformatics analysis revealed that P. oxalicum SL2 inhibited phosphate transport channels to suppress Cr­(VI) transport, facilitated iron and siderophore transport to store Fe, activated the glyoxylate cycle to survive harsh environments, and enhanced organic acid and riboflavin secretion to reduce Cr­(VI). Cr­(VI) exposure also stimulated the antioxidative system, promoting catalase activity and maintaining the intracellular thiol/disulfide balance. Cr­(VI)/Fe­(III) reductases played crucial roles in the intracellular reduction of chromium and iron, while nZVI decreased cellular oxidative stress and alleviated Cr­(VI) toxicity to P. oxalicum SL2. Overall, the P. oxalicum SL2–nZVI synergistic system is a promising approach for regenerating Fe­(II) while reducing Cr­(VI).

Transcriptomics extract the key chromium resistance genes of Cellulomonas

“…When Cr(VI) is transported into microbial cells in the form of chromate via proteins such as sulfate, phosphate, and molybdate transporters, initiating intracellular Cr(VI) reduction will be the key mechanism of microbial resistance to Cr(VI) toxic damage. For intracellular Cr(VI) reduction, a series of soluble reductase-mediated enzymatic reductions are important pathways for microbial intracellular resistance to Cr(VI) [32]. When C. mi Clb-11 is subjected to 0.5 mM Cr(VI) stress, the expression of cytochrome c subunit encoding genes qcrA and qcrC, as well as cytochrome c oxidase subunit encoding genes coxB and coxC, are signi cantly upregulated (Fig.…”

Synergy of carboxymethyl cellulose stabilized nanoscale zero-valent iron and Penicillium oxalicum SL2 to remediate Cr(VI) contaminated site soil

“…Furthermore, nZVI promoted oxalic acid secretion by SL2, and its generated iron ions could accelerate the reduction of Cr(VI) by oxalic acid (Hug et al, 1997). Studies have detected the formation of compounds containing Fe(II), Cr(V), and oxalate salts (HCrFeC 4 O 9 ) (Luo et al, 2023), providing crucial evidence for the involvement of Fe(II)/Fe(III) cycling in organic acid reduction of Cr(VI). In the case of the reaction group with only SL2 added, the removal efficiency for Cr(VI) increased with prolonged incubation time within the 30-day period, suggesting that SL2 successfully colonized and persisted in the soil, continuously fixing Cr(VI) through biological processes, in accordance with SL2 biomass change (Supplementary Figure S4).…”