Degradation microbial communities and metabolic characteristics of 2,4,6-tribromophenol in cold seep sediments

Abstract:

[Background] 2,4,6-tribromophenol (TBP) is a typical halogenated organic contaminant with high environmental persistence, bioaccumulation potential, and biological toxicity, posing serious threats to marine ecosystems. Cold seep sediments harbor diverse anaerobic microbial communities, which may contain functional microorganisms with the function of reductive dehalogenation of organohalides. [Objective] We investigated the microbial communities with the function of TBP degradation from cold seep sediments and characterized their taxonomic composition and metabolic potential, aiming to lay a research foundation for isolating anaerobic reductive dehalogenating microorganisms from cold seep sediments and provide microbial evidence supporting the bioremediation of halogenated pollutants. [Methods] With TBP as the sole electron acceptor, anaerobic reductive dehalogenating microorganisms were isolated from the sediment samples collected at four depths of a marine cold seep. Metagenomic sequencing was performed to analyze the microbial community composition, rdhA distribution, and metabolic characteristics. [Results] All enrichment cultures exhibited TBP debromination activity, with Pseudomonadota and Bacillota identified as the dominant bacterial phyla. Notably, the enrichment culture derived from the 150 cm sediment layer below the seafloor showed the highest TBP degradation efficiency. Moreover, this culture contained the greatest number and highest abundance of rdhA, which were eight to 12 times higher than those in the other three enrichment cultures. A total of 23 high-quality metagenome-assembled genomes (MAGs) carrying rdhA were recovered, all of which belonged to Bacillota. On the basis of GTDB taxonomy and average nucleotide identity analysis, several putative reductive dehalogenating microorganisms were identified, most of which have not yet been isolated or cultivated. In addition, metabolic pathway analysis based on ten high-quality non-redundant MAGs (completeness>90%) indicated that these organohalide-respiring bacteria generally lacked a complete de novo cobalamin biosynthesis pathway, but all were capable of synthesizing functional cobalamin via the salvage pathway. [Conclusion] These findings expand our understanding of the taxonomy and functional diversity of reductive dehalogenating microorganisms in cold seep environments and contribute to the exploration and utilization of deep-sea microbial resources.