Bacterial conversion of depolymerized Kraft lignin

Area of Science:

• Biotechnology
• Microbial Engineering
• Biorefining

Background:

• Lignin, a complex biopolymer, is a potential feedstock for chemical production.
• Native or technical lignin exhibits low degradation rates, necessitating depolymerization for efficient microbial conversion.
• Softwood Kraft lignin was subjected to base-catalyzed depolymerization to enhance its suitability for bioconversion.

Purpose of the Study:

• To evaluate the microbial growth of selected bacterial strains on depolymerized lignin.
• To identify bacterial candidates capable of consuming depolymerized lignin fragments.
• To understand the differential utilization of lignin components by bacterial strains.

Main Methods:

• Base-catalyzed depolymerization of softwood Kraft lignin using NaOH (5 wt%) in a continuous-flow reactor.
• Cultivation of nine bacterial strains from Pseudomonas and Rhodococcus genera on alkaline-treated lignin as a sole carbon source.
• Liquid cultivations and Size Exclusion Chromatography (SEC) to analyze lignin consumption and molecular weight changes.

Main Results:

• Pseudomonas fluorescens and Rhodococcus opacus demonstrated the best growth on lignin.
• Rhodococcus opacus consumed low molecular weight lignin compounds (0.1-0.4 kDa), including guaiacol.
• Pseudomonas fluorescens showed a shift towards lower average molecular weights, indicating degradation of larger lignin fractions.

Conclusions:

• Rhodococcus opacus and Pseudomonas fluorescens are identified as potential microbial candidates for depolymerized lignin bioconversion.
• These bacteria act on different molecular weight fractions of depolymerized lignin.
• Findings are relevant for designing efficient bioconversion processes for softwood Kraft lignin.