Application of R. Palustris in simulated wastewater purification and the degradation mechanism of crystal violet

Abstract

Azo dyes and triphenylmethane dyes poses a large threat to human health, There are many ways to degrade dyes while biodegraded are considered simpler, environmentally friendly, and economical. This study have researched the ability of Rhodopseudomonas palustris (R. palustris) to degrade multiple dyes. In this study, the ability of R. palustris to degrade multiple dyes was investigated. Specifically, the degradation efficiency of R. palustris for crystal violet (CV), malachite green (MG), congo red (CR), as well as COD, inorganic phosphorus, nitro, and nitroso compounds in simulated wastewater was evaluated using colorimetric methods. CV was selected for further analysis, and its intermediate metabolites were characterized using UV-vis spectroscopy, GC-MS, and HPLC-MS. Additionally, the gene expression levels of key enzymes involved in CV degradation were analyzed by RT-PCR, and a potential degradation pathway for CV was proposed. The results demonstrated that the degradation rates of CV, MG, and CR in simulated wastewater reached 97%, 92%, and 58%, respectively. Meanwhile, the degradation rates of COD, inorganic phosphorus, nitro, and nitroso compounds were up to 89.51%, 92.83%, 86.49%, and 85.91%, respectively. The intermediate metabolites of CV degradation by R. palustris included leucocrystal violet, triphenylmethane, and phenol. Notably, the gene expression levels of NADH-QO, NADH-FO, P450, Mett, and Nir were upregulated in the presence of CV. Based on these findings, a potential degradation pathway for CV by R. palustris was proposed: CV undergoes deamination via nitroreductase, followed by triphenylmethane cleavage into benzene and methylbenzene through oxidoreductases. Methylbenzene is then converted to phenol by methyltransferase. Although a potential degradation pathway for CV by R. palustris has been proposed, it remains a hypothesis. It still need to comprehensively investigate the genes associated with dye degradation in R. palustris through transcriptomics and to further validate the crystal violet degradation pathway proposed in this study.