We examined bacteria capable of transforming lignin-derived compounds into industrially or economically valuable substances from the seawater after the Great East Japan Earthquake-caused tsunami. Pseudomonas sp. ITH-SA-1 produced water-soluble fluorescent substances from the lignin-derived aromatic, syringaldehyde (SYAL). They: are polymeric substances derived from 3-O-methyl gallate produced through transformation of SYAL via syringate; are not known compounds reported previously; have excitation/emission peaks at 365/498 nm, respectively; and have an average molecular weight of 7.2 kDa. Despite the fact that aromatic structure generally plays an important role in the planarity and rigidity of organic fluorescent substance, the spectroscopic analyses revealed that aromatic rings were not detected in the molecules. Their activity is particularly rare and the biotransforming capabilities will contribute to the development of new basic techniques for the effective utilization of lignin.

We recently reported that Pseudomonas sp. ITH-SA-1 can transform the lignin-derived aromatic compound syringaldehyde (SYAL) into nonaromatic polymeric substances with fluorescent activity (NAPSFA). NAPSFA are particularly rare organic substances that fluoresce despite the absence of aromatic rings. In this study, we developed a simple method for producing NAPSFA using a nonbiological process. Incubation of the SYAL metabolite 3-O-methyl gallate (3-MGA) produced by Pseudomonas sp. ITH-SA-1 with Marine Broth (MB) or Luria−Bertani broth (LB) produced fluorescence even in the absence of bacteria, suggesting that fluorescent substances were produced from 3-MGA by a nonbiological process. 3-MGA reacted with tryptone and peptone, which are the primary nitrogen and phosphate sources in MB and LB, to produce the fluorescent substances. The fluorescent substances produced by the reaction of 3-MGA with tryptone exhibited excitation and emission peaks at 370 and 505 nm, respectively, which are nearly identical to those of NAPSFA (365/498 nm). The average molecular weight of the fluorescent substances (4.2 kDa) was lower than that of NAPSFA (7.2 kDa). ATR-FTIR and NMR analyses revealed that the molecules contained no aromatic rings, similar to NAPSFA. Our results demonstrate that nonaromatic fluorescent substances can be synthesized via a simple chemical reaction.