Performance, kinetics, and mechanism of 1,2,3-trimethylbenzene biodegradation by a newly isolated marine microalga

Recently, marine pollution by the accidental spills of C9 aromatics has raised public concerns, especially for 1,2,3-trimethylbenzene (1,2,3-TMB) because it is high-toxic and refractory. However, insufficient understanding of molecular mechanism underlying the biodegradation of 1,2,3-TMB hindered research on its bioremediation. In addition, microalgae-mediated bioremediation is popular due to its eco-friendliness and carbon sequestration. In this study, a marine diatom with degradation capability of 1,2,3-TMB, Chaetoceros sp. QG-1, was isolated from coastal area of Quangang, China. According to kinetics, the degradation efficiency of 1,2,3-TMB was the highest at 5 mg/L (K = 0.237/d) compared with other concentrations. Furthermore, the degradation mechanism of 1,2,3-TMB by Chaetoceros sp. QG-1 was revealed through analysis of degradation products and omics. 1,2,3-TMB was converted into 2,3-dimethylbenzoic acid and 2-hydroxypropionic acid by enzymes including non-heme Fe (II) and 2-oxoglutarate-dependent (2OG Fe (II)) oxygenase, UDP-glucose-6-dehydrogenase, aldehyde dehydrogenase, and other short-chain dehydrogenases, wherein, 2OG Fe (II) oxygenase was identified as the key enzyme to oxidize 1,2,3-TMB. This study provided species and theoretical supports for the bioremediation of marine environments contaminated with 1,2,3-TMB.