Fig. 3

SEC (a–c) and UHPLC (d–f) chromatograms of 1 g/L depolymerization lignin on day 0, 4 and 14 after bacterial conversion by R. opacus, P. fluorescens and P. putida EM42. The bacterial cultures, which were inoculated with a single colony, were grown using depolymerized lignin as the only carbon source in M9 medium. In the UHPLC chromatograms (d–f), the peaks at retention time 1.6, 2.4, 3.5, 4.6 and 4.7 min were identified as 4-HBA, vanillate, vanillin, guaiacol and acetovanillone, respectively. The consumption of low molecular weight fraction (0.1–0.4 kDa) by R. opacus within 4 days is highlighted with a green dashed circle. The consumption of monomers (vanillin and guaiacol) by R. opacus is highlighted with green arrows