Biodegradation of benzene homologues in contaminated sediment of the East China Sea

► To enrich moderately halophilic to degrade BTEX in a wide range of salinity. ► The optimal degradation was 120mg/L toluene within 5d in the presence of 2M NaCl. ► Marinobacter, Prolixibacter, Balneola, Zunongwangia, Halobacillus were the dominant genus. ► Ring fission was catalysed by catechol 1,2-dioxygenase and catechol 2,3-dioxygenase. ► Bacteria adjusted osmotic pressure by ectoine and hydroxyectoine as compatible solutes. This study focused on acclimating a microbial enrichment to biodegrade benzene, toluene, ethylbenzene and xylenes (BTEX) in a wide range of salinity. The enrichment degraded 120mg/L toluene within 5d in the presence of 2M NaCl or 150mg/L toluene within 7d in the presence of 1–1.5M NaCl. PCR–DGGE (polymerase chain reaction–denatured gradient gel electrophoresis) profiles demonstrated the dominant species in the enrichments distributed between five main phyla: Gammaproteobacteria, Sphingobacteriia, Prolixibacter, Flavobacteriia and Firmicutes. The Marinobacter, Prolixibacter, Balneola, Zunongwangia, Halobacillus were the dominant genus. PCR detection of genotypes involved in bacterial BETX degradation revealed that the degradation pathways contained all the known initial oxidative attack of BTEX by monooxygenase and dioxygenase. And the subsequent ring fission was catalysed by catechol 1,2-dioxygenase and catechol 2,3-dioxygenase. Nuclear magnetic resonance (NMR) spectroscopy profiles showed that the bacterial consortium adjusted the osmotic pressure by ectoine and hydroxyectoine as compatible solutes to acclimate the different salinity conditions.