Genome-Centric Metatranscriptomic Characterization of a Humin-Facilitated Anaerobic Tetrabromobisphenol A-Dehalogenating Consortium

Abstract

Tetrabromobisphenol A (TBBPA), a widely used brominated flame retardant in electronics manufacturing, has caused global contamination due to improper e-waste disposal. Its persistence, bioaccumulation, and potential carcinogenicity drive studies of its transformation and underlying (a)biotic interactions. This study achieved an anaerobic enrichment culture capable of reductively dehalogenating TBBPA to the more bioavailable bisphenol A. 16S rRNA gene amplicon sequencing and quantitative PCR confirmed that successive dehalogenation of four bromide ions from TBBPA was coupled with the growth of both <i>Dehalobacter</i> sp. and <i>Dehalococcoides</i> sp. with growth yields of 5.0 ± 0.4 × 10⁸ and 8.6 ± 4.6 × 10⁸ cells per μmol Br^- released (<i>N</i> = 3), respectively. TBBPA dehalogenation was facilitated by solid humin and reduced humin, which possessed the highest organic radical signal intensity and reducing groups -NH₂, and maintained the highest dehalogenation rate and dehalogenator copies. Genome-centric metatranscriptomic analyses revealed upregulated putative TBBPA-dehalogenating <i>rdhA</i> (reductive dehalogenase) genes with humin amendment, <i>cprA</i>-like <i>Dhb_rdhA1</i> gene in <i>Dehalobacter</i> species, and <i>Dhc_rdhA1/Dhc_rdhA2</i> genes in <i>Dehalococcoides</i> species. The upregulated genes of lactate fermentation, <i>de novo</i> corrinoid biosynthesis, and extracellular electron transport in the humin amended treatment also stimulated TBBPA dehalogenation. This study provided a comprehensive understanding of humin-facilitated organohalide respiration.