Isolation and characterization of bacteria capable of metabolizing lignin-derived low molecular weight compounds

Lignin, a major component of biomass, composed of homogeneous phenolic monomers and functions as a synthetic precursor in the production of specialty chemicals or polymers. In this study, bacterial strains that metabolize lignin-derived low molecular weight compounds (LLCs) were cultured which are capable of LLC bioconversion. We used an LLC mixture primarily composed of vanillin (VL), syringaldehyde (SA), vanillic acid (VA) and p-hydroxybenzoic acid which were prepared from a commercial alkaline lignin product. Enrichment culture was repeated twice in a medium containing the soil sample, the LLCs and inorganic salts. Three bacterial strains belonging to the genera Pseudomonas, Ochrobactrum, and Klebsiella were isolated. We found that only VL, SA, and VA were metabolized by the Pseudomonas strain, which was then found to grow in a medium with VL or VA as the sole source of carbon and energy. The VL isomers, namely, ovanillin and isovanillin were converted to the corresponding carboxylic acids but were not utilized as carbon sources by Pseudomonas. VL and VA are intermediates in the pathway of bacterial degradation of eugenol via ferulic acid. Several bacterial strains that metabolize VL, eugenol, and ferulic acid have been reported but such strains are rarely isolated from enrichment culture medium containing LLCs, due to insufficient induction by the precursors in the LLC medium. In this study, we demonstrated that the microorganisms involved in the bioconversion of LLCs can be isolated from simple enrichment culture.