Isolation and characterization of malachite green-removing yeast from a traditional fermented fishery product

The screening of malachite green (MG)-degrading microorganisms was carried out using various sources, namely, fish farms and a traditional fermented fishery product in Myanmar and Thailand. The enrichment culture method was performed using MG-containing broth media, and colonies that showed the decolorization of MG on plate media were isolated as MG-degrading candidates. From the results of the sequencing of the D1/D2 domain of the 26S rRNA gene, strain M3, a representative strain of MG-degrading candidates was identified as a halotolerant yeast, Debaryomyces nepalensis. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis indicated that during the incubation of this strain, the MG concentration gradually decreased and eventually reached undetectable levels. Conversely, the concentration of leucomalachite green (LMG) increased, and the final amount of LMG in the broth culture was estimated to be approximately 40 % of the initial MG amount. In addition, results of proton nuclear magnetic resonance spectroscopy (H-1-NMR) analysis also showed that MG and the tautomer of MG or other aromatic decomposition products of MG were not detected as a major component at the end of incubation. These results suggest that strain M3 removed MG and changed approximately 40 % to LMG and 60 % to some metabolites other than LMG.