Aqueous-based lignin extractions from birch, wheat, and oat exhibit broad antimicrobial activities

We studied aqueous-based lignin solutions from birch chips, wheat straw, and oat husks isolated with a gentle alkaline procedure after hemicellulose removal using pressurized hot-water-extraction. All lignin samples showed antiviral efficacy against tested non-enveloped enteroviruses and enveloped coronaviruses. Lignin from birch chip showed greatest efficacy against enteroviruses while wheat straw was almost as efficient but oat much less efficient. This is likely due to higher total phenolics in birch and wheat and highest syringyl content in birch. The detailed mechanistical studies confirmed that lignin treatment stabilized CVA9 structure and led to virus aggregation. Lignin-treated CVA9 could still bind and enter cells but did not proceed with replication in cells. In contrast to stabilization of enteroviruses, lignin treatment damaged the coronavirus structure leading to inhibition of viral entry and infection. All lignin samples significantly delayed the growth of Gram-positive Staphylococcus aureus and reduced the population density of Gram-negative Escherichia coli. Furthermore, morphological changes could be observed for both bacterial strains. Altogether, lignins demonstrated broadly acting antimicrobial efficacy, acting directly on the microbes. The results further suggest that differences in efficacy among microbes are likely based on structural differences of microbes but also structural differences of lignins from different sources.