Revealing the driving mechanism of efficient microbial degradation of aromatic compounds with phenol as co-substrate from gene transcription level

Abstract

The excessive content of aromatic compounds was a key factor restricting the difficult discharge of various industrial wastewater. In this study, the microbial enhanced degradation characteristics of aromatic compounds were investigated with naphthalene, phenanthrene, and pyrene were selected as representative, and phenol as co-substrate. Furthermore, the driving mechanisms of microbial-enhanced degradation of aromatic compounds were revealed from the perspectives of enzyme activity and gene transcription levels. The results indicated that the initiation degradation times for naphthalene, phenanthrene, and pyrene were advanced by 4, 6 and 6 h, respectively, with phenol as co-substrate. Correspondingly, the metabolic rates increased by 56.63 %, 46.24 %, and 35.38 %, respectively. Further mechanism analysis showed that the initial dioxygenase NDO (Key enzymes catalyzing the preliminary oxidation of aromatic rings) activity increased by 1.25–1.89 fold and was expressed 12 h earlier due to the co-substrate. The expression of genes ubiH and ygiD encoding the key enzymes 2-octenyl-6-methoxyphenol hydroxylase and 4,5-DOPA exodiol dioxygenase related to degradation initiation was upregulated by 2.25–4.45 fold and 3.04–4.04 fold, respectively. Additionally, the expression of genes encoding key enzymes associated with further ring-opening cleavage—namely aldB, phdI, dmpB, catA, pht3, pht5, and ligA—was significantly upregulated, and the activities of C23O and C21O were markedly enhanced. Additionally, several genes related to carbohydrate, amino acid, and TCA cycle metabolism were found to be upregulated, effectively promoting the cooperation between various metabolic pathways and facilitating ATP synthesis, which provided more energy for microbial metabolism. Therefore, this study provided reliable theoretical basis for efficient degradation of aromatic compounds.