Metatranscriptomic Insights into Aerobic Biotransformation of 6:2 Fluorotelomer Sulfonate by an Enrichment Culture under Sulfur-Limiting Conditions

6:2 Fluorotelomer sulfonate (6:2 FTS), an alternative for PFOS, has become an environmental concern due to its toxicity. This study investigated the aerobic biotransformation of 6:2 FTS under sulfur-limiting conditions using an enrichment culture, SXC01. The enriched culture achieved ≥99.5% degradation of 6:2 FTS at initial concentrations of 0.5, 2.5, and 5 mg/L within 14 days, with notable corresponding defluorination ratios of 77.2%, 28%, and 16.8%, respectively. Eleven transformation products were identified and quantified over time, and the accumulation of intermediate product 6:2 FTUCA suggested that its further degradation may represent a rate-limiting step. Furthermore, the production of PFHxA is more significant than that of PFBA, suggesting the transformation of 6:2 FTUCA via 5:2 sFTOH pathway is more dominant than the other proposed alternative pathway. Metatranscriptomic analysis revealed the upregulation of key genes associated with desulfonation (e.g., <i>ssuEADCB</i> cluster, <i>cysI</i>, <i>sbp</i>, <i>iscS</i>) and defluorination (e.g., <i>ladA</i>, <i>dehH</i>, <i>crcB</i>, <i>dhaA</i>), indicating a synergistic metabolic network driving 6:2 FTS biotransformation. Active genera identified included <i>Brucella</i>, <i>Rhodococcus</i>, and <i>Pseudoclavibacter</i>. Moreover, the predominant <i>Brucella anthropi</i> SX009 was successfully isolated and shown to completely degrade 6:2 FTS within 14 days. This study provides novel insights into the mechanisms of 6:2 FTS biotransformation.