Methyl syringate: An efficient phenolic mediator for bacterial and fungal laccases

► The mechanism for phenolics oxidation by bacterial laccases is proposed for the first time. ► The efficiency of laccase-mediator system using phenolics is independent of the enzymes properties. ► Reactivity vs. stability of phenoxy radicals is a key issue in the laccase-mediator systems. ► C-O coupling products were identified from a newly putative radical coupling route. ► A catalytic cycle of laccase-mediator systems with an interplay of competitive routes is proposed.