Biodegradation of kraft lignin by newly isolated Klebsiella pneumoniae, Pseudomonas putida, and Ochrobactrum tritici strains

Bacterial systems have drawn an increasing amount of attention on lignin valorization due to their rapid growth and powerful environmental adaptability. In this study, Klebsiella pneumoniae NX-1, Pseudomonas putida NX-1, and Ochrobactrum tritici NX-1 with ligninolytic potential were isolated from leaf mold samples. Their ligninolytic capabilities were determined by measuring (1) the cell growth on kraft lignin as the sole carbon source, (2) the decolorization of kraft lignin and lignin-mimicking dyes, (3) the micro-morphology changes and transformations of chemical groups in kraft lignin, and (4) the ligninolytic enzyme activities of these three isolates. To the best of our knowledge, this is the first report that Ochrobactrum tritici species can depolymerize and metabolize lignin. Moreover, laccase, lignin peroxidase, and Mn-peroxidase showed high activities in P. putida NX-1. Due to their excellent ligninolytic capabilities, these three bacteria are important supplements to ligninolytic bacteria library and could be valuable in lignin valorization.