Biodegradation of kraft lignin by a bacterial strain Sphingobacterium sp. HY-H

A lignin-degrading bacterium was isolated on mineral salt medium amended by lignosulfonate (L-MSM) agar from the activated sludge of a pulp and paper mill wastewater treatment plant and identified as Sphingobacterium sp. HY-H by biochemical tests and 16S rRNA gene sequencing. The maximum kraft lignin (KL) degradation capability of strain HY-H was determined to be 28.2% on a COD basis under the optimal conditions of pH 7.0, temperature 30°C, and KL to nitrogen (as NH₄Cl) ratio of 2 by mass. Moreover, growth kinetic studies showed the KL tolerance of strain HY-H was relatively high and the analysis of KL degradation products by GC-MS revealed the formation of low-molecular-weight aromatic compounds (LMWACs), such as guaiacol, vanillin and vanillyl alcohol, indicating that the strain HY-H can oxidize guaiacyl (G) units and syringyl (S) units in lignin structure. In addition, some low molecular ketone compounds such as 4-hydroxy-2-butanone and methyl vinyl ketone were detected in the inoculated sample after 48h, further validating the partial but possible degradation of KL by strain HY-H.