Biodegradation of 3,3′,4,4′-tetrachlorobiphenyl by Sinorhizobium meliloti NM

• This report is the first on the degradation of PCB 77 by Sinorhizobium meliloti.
• S. meliloti NM could effectively utilize PCB 77 (0.25–5 mg L−1) as a sole substrate.
• S. meliloti NM had maximum PCB 77 degradation in the presence of caffeic acid.
• Additional substrates might promote PCB 77-degradation via biofilm formation.
• The expression of benzoate metabolism-related genes was detected.

A rhizobial strain, Sinorhizobium meliloti NM, could use 3,3′,4,4′-tetrachloro-biphenyl (PCB 77) as the sole carbon and energy source for growth in mineral salt medium. The degradation efficiency of PCB 77 by strain NM and the bacterial growth increased with a decrease in PCB 77 concentration (5–0.25 mg L−1). The addition of secondary carbon sources, phenolic acids and one surfactant influenced PCB 77 degradation, rhizobial growth and biofilm formation. The highest degradation efficiency was observed in the presence of caffeic acid. Benzoate and chloride ions were detected as the PCB 77 metabolites. The up-regulation of benzoate metabolism-related gene expression was also observed using quantitative reverse transcription-polymerase chain reaction. This report is the first to demonstrate Sinorhizobium using coplanar tetrachlorobiphenyl as a sole carbon and energy source, indicating the potential wide benefit to the field of rhizobia-assisted bioremediation.