Degradation of benzyl ether bonds of lignin by ruminal microbes

We examined microbial activity in the rumen to cleave benzyl ether bonds of lignin model compounds that fluoresced when the bonds were cleaved. 4-Methylumbelliferone veratryl ether dimer was degraded completely within 8 h even in the presence of fungicidal antibiotics, but no significant degradation occurred with bactericidal antibiotics. Degradation of a phenolic beta-O-4 trimer incorporating 4-methylumbelliferone by a benzyl ether linkage was stimulated by ruminal microbes, although its corresponding non-phenolic model compound, 1-(4-ethoxy-3-methoxyphenyl)-1-O-(4-methylumbelliferyl)-2-(2-methoxyp henoxy)-3-propanol, was not degraded. A coniferyl dehydrogenation polymer bearing fluorescent beta-O-4 benzyl ether that contains both phenolic and non-phenolic benzyl ether bonds was partially degraded (about 20%) in 48 h. These results suggest that ruminal microbes decompose benzyl ether linkages of lignin polymers under anaerobic conditions.