Bacterial conversion of depolymerized Kraft lignin

Abstract

BackgroundLignin is a potential feedstock for microbial conversion into various chemicals. However, the microbial degradation rate of native or technical lignin is low, and chemical depolymerization is needed to obtain reasonable conversion rates. In the current study, nine bacterial strains belonging to the Pseudomonas and Rhodococcus genera were evaluated for their ability to grow on alkaline-treated softwood lignin as a sole carbon source.ResultsPseudomonas fluorescens DSM 50090 and Rhodococcus opacus DSM1069 showed the best growth of the tested species on plates with lignin. Further evaluation of P. fluorescens and R. opacus was made in liquid cultivations with depolymerized softwood Kraft lignin (DL) at a concentration of 1 g/L. Size-exclusion chromatography (SEC) showed that R. opacus consumed most of the available lower-molecular weight compounds (approximately 0.1–0.4 kDa) in the DL, but the weight distribution of larger fractions was almost unaffected. Importantly, the consumed compounds included guaiacol—one of the main monomers in the DL. SEC analysis of P. fluorescens culture broth, in contrast, did not show a large conversion of low-molecular weight compounds, and guaiacol remained unconsumed. However, a significant shift in molecular weight distribution towards lower average weights was seen after cultivation with P. fluorescens.ConclusionsRhodococcus opacus and P. fluorescens were identified as two potential microbial candidates for the conversion/consumption of base-catalyzed depolymerized lignin, acting on low- and high-molecular weight lignin fragments, respectively. These findings will be of relevance for designing bioconversion of softwood Kraft lignin.Electronic supplementary materialThe online version of this article (10.1186/s13068-019-1397-8) contains supplementary material, which is available to authorized users.

Bacterial Transformation of Aromatic Monomers in Softwood Black Liquor

“…Guaiacol, vanillin, and acetovanillone are the most abundant monoaromatic compounds in Lignoforce™ softwood BL. These are the same major monoaromatic compounds that have been reported in other depolymerized softwood lignin samples, including an oxidative depolymerized Lignoboost softwood kraft lignin (Abdelaziz et al, 2019), an alkaline depolymerized pine kraft lignin (Indulin AT; Prothmann et al, 2017;Ravi et al, 2019), and OCF pine lignin (Zhu et al, 2020). This suggests that these compounds are characteristic monoaromatic compounds generated by oxidative depolymerization of softwood lignin.…”

“…However, none of these strains completely degraded all the LDACs. Similarly, Ravi et al (2019) used an alkaline depolymerized softwood kraft lignin as substrate for bacterial conversion, demonstrating that two Pseudomonas strains grew on vanillate, vanillin, and 4-hydroxybenzoate, while a rhodococcal strain degraded these compounds as well as guaiacol. In this study, acetovanillone remained as the only persistent monoaromatic.…”

Biotransformation and Cytotoxicity Evaluation of Kraft Lignin Degraded by Ligninolytic Serratia liquefaciens

“…The <24 h sample was used as the control or untreated. These conditions were used as the standard conditions for all KL degradation/biotransformation experiments (Ravi et al, 2019).…”

Investigating Lignin-Derived Monomers and Oligomers in Low-Molecular-Weight Fractions Separated from Depolymerized Black Liquor Retentate by Membrane Filtration

“…The UHPLC experiments were performed on a Waters H-Class UHPLC system using a modified method described by Krithika et al [37]. The UHPLC system was equipped with a Waters BEH C18 column (100 × 2.1 mm, 1.7 µm) and run at 50 • C. Detection was performed using a PDA detector at 280 nm, with the baseline-corrected by 350-400 nm.…”