Innovative bioremediation of dexamethasone in aquatic ecosystems using Rhodococcus sp. D32: Pathway discovery and reduction of ecotoxicity

In response to the widespread environmental concern of endocrine disruptors, our research investigated the aerobic biodegradation of dexamethasone (DEX), a widely used synthetic glucocorticoid with endocrinedisrupting properties, by strain Rhodococcus sp. D32. This innovative strain showcases remarkable DEXdegrading capabilities, with the half-life for degrading 500 mu g/L DEX in MH broth being just 7.56 h. Utilizing high -resolution mass spectrometry, we identified six transformation products (TPs) and revealed a unique steroid nucleus -opening pathway marked by A -ring lactonization and subsequent lactone hydrolysis. This newly discovered pathway deviates from the classical steroid 9,10-seco pathways and previous transformations that preserved the intact steroid nucleus, thus expanding our knowledge of microbial steroid transformations. Additionally, the degradation process progressively converts the parent DEX into less ecotoxic products, significantly reducing the overall ecotoxicity of the system. This reduction remains evident when considering the combined toxicity of DEX and its TPs, indicating a promising approach for lessening environmental harm. Strain D32 also proved effective in various authentic aquatic environments, including fishpond water, urban sewage, river water, and reservoir water, where its introduction markedly expedited the dissipation of DEX. Our findings underscore the potential of strain D32 as a powerful tool for the bioremediation of DEX, presenting an efficient and eco-friendly strategy to alleviate the effects of this endocrine disruptor in aquatic ecosystems.