Lead immobilization assisted by fungal decomposition of organophosphate under various pH values

Abstract

Organic phosphates (OP) account for approximately 30–90% of total soil P. However, it is too stable to be utilized by plants as available P source. Aspergillus niger (A. niger) has considerable ability to secret phytase to decompose OP. Meanwhile, mineralization of lead (Pb) is efficient to achieve its remediation. This study hence investigated Pb immobilization by A. niger assisted decomposition of OP under variable acidic environments. A. niger can survive in the acidic environment as low as pH = 1.5. However, alternation of environmental pH within 3.5–6.5 significantly changed fungal phytase secretion. In particular, weakly acidic stimulation (pH of ~5.5) increased phytase activity secreted by A. niger to 0.075 µmol/min/mL, hence elevating P release to a maximal concentration of ~20 mg/L. After Pb addition, ATR-IR and TEM results demonstrated the formation of abundant chloropyromorphite [Pb5(PO4)3Cl] mineral on the surface of mycelium at pH = 5.5. Anglesite, with a higher solubility than pyromorphite, was precipitated massively in other treatments with pH lower or higher than 5.5. This study elucidated the great potential of applying OP for Pb immobilization in contaminated water.

Deposition of Lead Phosphate by Lead-Tolerant Bacteria Isolated from Fresh Water near an Abandoned Mine

“…As organic phosphate is abundant in soil, the use of inorganic phosphorus obtained by decomposition for lead deposition is being studied. Aspergillus niger precipitates lead as pyromorphite by the secretion of phytase [ 48 ].…”

Fungal Growth and Pathology

“…Most fungi survive and reproduce between pH 3 and 10. The optimum pH range is between 5 and 7 [20][21][22]. In addition, if the environment in which fungi are found in alkaline, they can achieve maximum growth by converting the pH of the environment to the optimum growth pH with the organic acids they secrete.…”

Heavy Metal Remediation by Dry Mycelium Membranes: Approaches to Sustainable Lead Remediation in Water

“…4 , lowering the bioavailability of lead. 30 However, heavy metal bioremediation using live fungal species faces limitations due to deployment that include challenges related to maintaining a viable environment for mycelium growth and concerns regarding their mechanical reliability during material handling. Recent advances have successfully harnessed the ability of mycelium to self-grow into microporous network structures of various shapes or textures.…”

“…Furthermore, live mycelium, through biogeochemical processes, especially in the presence of compounds, such as chlorine and phosphorus, can biomineralize metallic lead into stable lead compounds, including oxalates, phosphates, and carbonates, at the hyphal surface. 25,26 These biomineralization pathways, along with crystal compositions and kinetics, are influenced by several environmental factors, including the concentration and oxidation state of the heavy metal, 27 composition of organic matter, 28 availability of other inorganic elements, 29 and the pH of the environment, 30,31 which assist the formation of stable compounds. For example, Aspergillus niger fungi, in a weakly acidic environment (pH ∼ 5.5), displayed an increased enzymatic phytase activity, leading to the hydrolysis of organic phosphorus into inorganic phosphates.…”

“…These biopolymers present a variety of surface functional groups, including hydroxyl, amide, and carbonyl groups, which actively participate in the sorption of heavy metal ions via processes, such as electrostatic interactions, surface chelation, and ion exchange. − Rudakiya et al showed that heavy metals, such as Cd 2+ , Cr 2+ , and mixed metals, were adsorbed by the biopolymers present on the hyphal cell wall of white rot (Phanerochaete chrysosporium) mushrooms, resulting in sorption efficiencies exceeding 90% across a wide range of pH values. Furthermore, live mycelium, through biogeochemical processes, especially in the presence of compounds, such as chlorine and phosphorus, can biomineralize metallic lead into stable lead compounds, including oxalates, phosphates, and carbonates, at the hyphal surface. , These biomineralization pathways, along with crystal compositions and kinetics, are influenced by several environmental factors, including the concentration and oxidation state of the heavy metal, composition of organic matter, availability of other inorganic elements, and the pH of the environment, , which assist the formation of stable compounds. For example, Aspergillus niger fungi, in a weakly acidic environment (pH ∼ 5.5), displayed an increased enzymatic phytase activity, leading to the hydrolysis of organic phosphorus into inorganic phosphates.…”