HPLC chromatograms of the metabolism of caffeic acid by GK5 and GK12 strains and the production of vinylcatechol (VC): supernatants from GK5 and GK12 grown for 5 days in presence of caffeic acid. Line in black indicates that acetonitrile was used as mobile phase. Line in red indicates that ethanol was used as mobile phase. The chromatogram was recorded at 310 nm. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).