Oxalic acid, a secondary metabolite produced by fungi, bacteria, and plants, plays a significant role in various ecological and biotechnological processes. It is involved in nutrient availability, mineral weathering, metal precipitation, and the degradation of lignocellulose. Fungi, particularly white and brown rot fungi, are efficient in breaking down lignocellulose, with oxalic acid contributing to this process through its role as a chelating agent and in the formation of reactive oxygen species (ROS). Oxalic acid also influences biomineralization, the formation of calcium carbonate, and the oxalate-carbonate pathway (OCP), which is crucial for carbon sequestration in soil. Oxalic acid is synthesized through various biochemical pathways in fungi, involving enzymes such as oxaloacetase and glyoxylate dehydrogenase. It is degraded by fungi and bacteria through enzymes like oxalate decarboxylase and oxalate oxidase, which are involved in the metabolism of oxalate. These enzymes are important in biotechnological applications, such as the prevention of kidney stones, as diagnostic tools, and as antifungal agents. In the context of kidney disease, oxalate-degrading bacteria, such as Oxalobacter formigenes, and oxalotrophic bacteria like Lactobacillus and Bifidobacterium, are being explored as probiotics to reduce oxalate levels in the body. These bacteria can help in the degradation of oxalate, thus preventing the formation of calcium oxalate kidney stones. Oxalic acid also plays a role in plant pathology, particularly in the pathogenesis of Sclerotinia sclerotiorum, a plant pathogen. The acid contributes to the pathogenicity of the fungus by acidifying the environment, chelating calcium ions, and enhancing the activity of cell wall-depolymerizing enzymes. Additionally, oxalate oxidase and decarboxylase in plants can help in resisting infection by Sclerotinia sclerotiorum. The oxalate-carbonate pathway (OCP) is a biogeochemical process that links the oxidation of calcium oxalate and the precipitation of carbonate, leading to the formation of calcium carbonate. This pathway is important for carbon sequestration in soil and is a potential long-term sink for atmospheric CO₂. Fungi and bacteria play a crucial role in this process, with fungi acting as both oxalate producers and degraders. In conclusion, oxalic acid is a multifunctional compound with significant roles in environmental processes, biotechnology, and human health. Its involvement in the OCP and its potential applications in bioremediation, carbon sequestration, and the prevention of kidney stones highlight its importance in both ecological and industrial contexts.Oxalic acid, a secondary metabolite produced by fungi, bacteria, and plants, plays a significant role in various ecological and biotechnological processes. It is involved in nutrient availability, mineral weathering, metal precipitation, and the degradation of lignocellulose. Fungi, particularly white and brown rot fungi, are efficient in breaking down lignocellulose, with oxalic acid contributing to this process through its role as a chelating agent and in the formation of reactive oxygen species (ROS). Oxalic acid also influences biomineralization, the formation of calcium carbonate, and the oxalate-carbonate pathway (OCP), which is crucial for carbon sequestration in soil. Oxalic acid is synthesized through various biochemical pathways in fungi, involving enzymes such as oxaloacetase and glyoxylate dehydrogenase. It is degraded by fungi and bacteria through enzymes like oxalate decarboxylase and oxalate oxidase, which are involved in the metabolism of oxalate. These enzymes are important in biotechnological applications, such as the prevention of kidney stones, as diagnostic tools, and as antifungal agents. In the context of kidney disease, oxalate-degrading bacteria, such as Oxalobacter formigenes, and oxalotrophic bacteria like Lactobacillus and Bifidobacterium, are being explored as probiotics to reduce oxalate levels in the body. These bacteria can help in the degradation of oxalate, thus preventing the formation of calcium oxalate kidney stones. Oxalic acid also plays a role in plant pathology, particularly in the pathogenesis of Sclerotinia sclerotiorum, a plant pathogen. The acid contributes to the pathogenicity of the fungus by acidifying the environment, chelating calcium ions, and enhancing the activity of cell wall-depolymerizing enzymes. Additionally, oxalate oxidase and decarboxylase in plants can help in resisting infection by Sclerotinia sclerotiorum. The oxalate-carbonate pathway (OCP) is a biogeochemical process that links the oxidation of calcium oxalate and the precipitation of carbonate, leading to the formation of calcium carbonate. This pathway is important for carbon sequestration in soil and is a potential long-term sink for atmospheric CO₂. Fungi and bacteria play a crucial role in this process, with fungi acting as both oxalate producers and degraders. In conclusion, oxalic acid is a multifunctional compound with significant roles in environmental processes, biotechnology, and human health. Its involvement in the OCP and its potential applications in bioremediation, carbon sequestration, and the prevention of kidney stones highlight its importance in both ecological and industrial contexts.