Biodegradation of kraft lignin by a newly isolated anaerobic bacterial strain, Acetoanaerobium sp WJDL-Y2

An anaerobic kraft lignin (KL)-degrading bacterial strain was isolated from sludge of a pulp and paper mill. It was characterized as Acetoanaerobium sp. WJDL-Y2 by 16S rRNA gene sequencing. The maximum KL degradation capability of strain Y2 was determined to be 24.9% on a COD basis under an optimal condition with temperature of 31.5 degrees C, initial pH of 6.8 and KL to nitrogen (as NH4Cl) ratio of 6.5 by mass. Growth kinetic studies showed that the KL tolerance of strain Y2 was relatively high (K-i = 8120.45 mg l(-1)). Analysing KL degradation products by GC-MS revealed the formation of low-molecular-weight aromatic compounds (LMWACs), including benzenepropanoic acid, syringic acid and ferulic acid. This indicates that strain Y2 can oxidize lignin structure's p-hydroxyphenyl (H) units, guaiacyl (G) units and syringyl (S). In addition, the inoculated sample also contained low-molecular acid compounds, such as hexanoic acid, adipic acid and 2-hydroxybutyric acid, further validating strain Y2's ability to degrade KL.