Recent research has focused on identifying cost-effective alternatives to conventional substrates used in polyhydroxyalkanoic acid (PHA) production. Among these, lignin—a complex aromatic polymer and the second most abundant organic compound on Earth after cellulose—has gained attention. Lignin is commonly discarded as a byproduct of paper and agricultural industries, yet its recalcitrant structure makes it difficult to biodegrade. However, during industrial processing, lignin is partially broken down into phenolic compounds such as ferulic acid, which are more amenable to microbial utilization. Despite this, the potential of these phenolic degradation products as substrates for PHA production has not been thoroughly explored.

In this study, we assessed the ability of various microorganisms to utilize lignin-derived phenolic compounds, with the ultimate goal of enabling PHA production from lignin waste streams. Strains from the genera Comamonas, Sphingobium, and Pseudomonas, known for both phenolic compound degradation and PHA biosynthesis, were tested. Four representative lignin-derived compounds—ferulic acid, p-coumaric acid, vanillin, and 4-hydroxybenzoic acid—were used as sole carbon sources in minimal salts (MS) medium. Each compound was dissolved in ethanol and added at concentrations of 0.1 g/L and 0.5 g/L, reflecting levels typically found in acid hydrolysates and kraft pulp.

The experimental results showed that Sphingobium jiangsuense (NBRC 112973) was able to grow on ferulic acid and vanillin, while Sphingobium sp. (NBRC 103272) utilized only ferulic acid. Pseudomonas putida (NBRC 100988) grew on all tested compounds except ferulic acid. These results demonstrate that the tested strains can metabolize a range of lignin-derived phenolics.

Based on these findings, we aim to further evaluate PHA production using these strains with individual or mixed phenolic substrates to assess production yields and overall feasibility.