An Absorption Mechanism for the Decolorization of Melanoidin by Rhizoctonia sp. D-90

Abstract

Rhizoctonia sp. D-90 decolorized molasses melanoidin medium and a synthetic melanoidin medium by 87.5% and 84.5%, respectively, under experimental growth conditions. Mycelia grown in solutions of melanoidin turned dark brown. However, the melanoidin (dark brown in color) could be eluted from the mycelia by washing in a solution of NaOH, and the maximum yield of melanoidin from mycelia reached 96. 1%. Mycelia grown in potato dextrose medium did not have any electron-dense materials in the cytoplasm or around the cell membrane, but when such mycelia were transferred to melanoidin media, abundant electron-dense material appeared in the cytoplasm and around cell membranes. Subsequently, the electron-dense materials disappeared when the mycelia were returned to the potato dextrose medium for further growth. The mechanism of decolorization of melanoidin by Rhizoctonia sp. D-90 involved absorption of the melanoidin pigment by the cells as a macromolecule and its intracellular accumulation in the cytoplasm and around the cell membrane as a melanoidin complex, which was then gradually decolorized by intracellular enzymes.