Fungal peptidomelanin: a novel metabolite for the amelioration of soil heavy metal toxicity

Heavy metal contamination of agricultural soils reduces crop yields, contaminates groundwater and disrupts local ecosystems. Here, we describe a novel, water-soluble form of melanin (peptidomelanin) capable of chelating heavy metals in large quantities. Peptidomelanin is composed of an L-DOPA core polymer that is solubilized via short, heterogeneous peptide chains with a mean amino acid length of ∼2.6. It is secreted by the spores of Aspergillus niger melanoliber during germination. It was found to chelate large quantities of lead, mercury, and uranyl. It increased the germination rate, seed mass, and shoot length of wheat planted in substrate contaminated with 100 ppm mercury. Therefore, peptidomelanin may increase crop yields in contaminated agricultural soils treated in situ with the substance.