Underexplored Organohalide-Respiring Bacteria in Sewage Sludge Debrominating Polybrominated Diphenyl Ethers

Polybrominated
diphenyl ethers (PBDEs) are persistent organic pollutants
prevalent in the environment. Organohalide-respiring bacteria (OHRB)
can attenuate PBDEs via reductive debromination, but often producing
toxic end-products. Debromination of PBDEs to diphenyl ether remains
a rare phenomenon and is so far specifically associated with Dehalococcoides isolated from e-waste polluted sites. The
occurrence of PBDE debromination in other ecosystems and underpinning
OHRB are underexplored. Here we found that debromination of PBDEs
is a common trait of sewage sludge microbiota, and diphenyl ether
was produced as the end-product at varying quantities (0.6–52.9%
mol of the parent PBDEs) in 76 of 84 cultures established with bioreactor
sludge. Diverse debromination pathways converting PBDEs to diphenyl
ether, including several new routes, were identified. Although Dehalococcoides contributed to PBDE debromination, Dehalogenimonas, Dehalobacter, and uncultivated
Dehalococcoidia likely played more important roles than previously
recognized. Multiple reductive dehalogenase genes (including bdeA, pcbA4, pteA, and tceA) were also prevalent and coexisted in bioreactor sludge.
Collectively, these findings contribute to enhancing our comprehension
of the environmental fate of PBDEs, expanding the diversity of microorganisms
catalyzing PBDE debromination, and developing consortia for bioremediation
application.