Biodegradation of 1,2,4-trimethylbenzene in seawater using Rhodomonas sp. JZB-2: Performance, kinetics, and mechanism.

Recently, marine ecosystems have been threatened by an accidental spill of C9 aromatics, particularly 1,2,4-trimethylbenzene (1,2,4-TMB), due to its high proportion in C9 aromatics. Microalgae-mediated bioremediation is a promising approach for pollutant removal owing to its eco-friendliness and carbon sequestration potential. In this study, the marine Cryptophyta Rhodomonas sp. JZB-2 demonstrated the ability to completely degrade 1-40 mg/L of 1,2,4-TMB within 6 days, showcasing its advantage in degrading 1,2,4-TMB at high concentrations compared to other microorganisms in the literature. Transcriptomics and proteomics analysis showed that several enzymes involved in 1,2,4-TMB degradation were significantly upregulated: hydroxylase (JmjC domain), iron/manganese-superoxide dismutase, and alcohol dehydrogenase etc. A new insight of biodegradation mechanism was elucidated that 1,2,4-TMB was initially oxidized by hydroxylase (JmjC domain) to 2,3,6-trimethylphenol, a process accelerated by the overexpression of iron/manganese-superoxide dismutase. Subsequently, 2,3,6-trimethylphenol was further degraded into 5-methylhexanoic acid via alcohol dehydrogenase and other short-chain dehydrogenases. Notably, the degradation products were less toxic than the parent compound (1,2,4-TMB). This study highlights the potential of Rhodomonas sp. JZB-2 for bioremediation of seawater contaminated with 1,2,4-TMB.