Anaerobic degradation of acid red 73 by obligately aerobic Aspergillus tabacinus LZ-M though a self-redox mechanism

Abstract

Fungi are potential biological resources for refractory organics degradation, but their anaerobic degradation of azo dyes are rarely reported. In this study, a fungus Aspergillus tabacinus LZ-M was isolated grown aerobically and degraded acid red 73 (AR73) with a decolorization rate of 90.28% in 5 days at 400 mg/L of concentration anaerobically. Metabolic pathway showed that AR73 was reduced into 2-hydroxynaphthalene and aniline then mineralized into CO2. The anaerobic self-redox process revealed electrons generated in carbon oxidation and transferred to -C-N= and -N=N, resulting in complete mineralization of AR73 in strain LZ-M. Data of transcriptome analysis showed that the benzene compounds produced from AR73 by declorizing reductase entered the catechol pathway and glycolysis process to mineralize. Enzymes involved in aromatics degradation, glycolysis processes, cytochrome C and quinone oxidoreductases were up-regulate, but the key reductase responsible to cleave AR73 to phenylhydrazine was not found. A novel enzyme Ord95 containing a glutamate S-transferase domain was identified in the unknown genes as a reductase which cleaving -C-N= in AR73 using NADH as electron donor, and three arginines key active sites. These observations reveal a new degradation mechanism of AR73 in strain LZ-M which would be potential candidate for treatment of azo dyes wastewater.Graphical abstract