Synthetic dye decolorization using the marine filamentous fungus Pestalotiopsis disseminata AN-7 and toxicity evaluation using Daphnia magna

Biological treatment using microorganisms is an alternative low-cost wastewater treatment method with minimal environmental impact. However, there have been few studies on such purification technologies in marine environments. Moreover, for practical application, an appropriate safety assessment accounting for the impact on the ecosystem is necessary. To fill this gap, the aim of this study was to evaluate the efficacy of the marine fungal strain Pestalotiopsis disseminata AN-7 isolated from mangroves in Iriomote Island (Okinawa, Japan) in decolorizing synthetic dyes in the presence of salt and the changes in ecotoxicity during the decolorization process. The acute inhibition test for the azo dye Reactive Red 120 (RR120) and the xanthene dyes Food Red No. 104 (FR104) and Food Red No. 105 (FR105) showed half-maximal effective concentrations of 20.6, 12.1, and 0.69 mg/L to inhibit swimming of Daphnia magna . Pestalotiopsis disseminata AN-7 showed decolorization ratios of 75.6%, 60.6%, and 96.6%, respectively, and decolorization was also visually verified. A maximum decolorization ratio of 89.3% was obtained for a mixture of the three dyes. After decolorization, inhibition rates significantly decreased from 81.7 to 1.7% for RR120, 83.3 to 40% for FR104, 100 to 25% for FR105, and 100 to 18.3% for the dye mixture. High decolorization ratios (59.1–96.0%) were also maintained under NaCl concentrations of 1.5–3%. This study confirms the usefulness and safety of microorganisms for marine bioremediation in decolorizing synthetic dyes, even in the presence of salt and high dye concentrations, and further highlights the importance of acute toxicity assessments.