Bacterial conversion of depolymerized Kraft lignin

Area of Science:

• Microbiology
• Biotechnology
• Biochemistry

Background:

• Lignin, a complex biopolymer, is an abundant potential feedstock for microbial chemical conversion.
• Native or technical lignin exhibits low microbial degradation rates, necessitating chemical depolymerization for efficient bioconversion.
• Alkaline-treated softwood lignin was used as a sole carbon source to evaluate bacterial growth.

Purpose of the Study:

• To identify bacterial strains capable of utilizing depolymerized lignin as a carbon source.
• To assess the microbial degradation and consumption patterns of depolymerized softwood Kraft lignin (DL) by selected bacterial strains.
• To evaluate the potential of specific bacterial genera, Pseudomonas and Rhodococcus, for lignin bioconversion.

Main Methods:

• Screening of nine bacterial strains from the Pseudomonas and Rhodococcus genera for growth on lignin.
• Liquid cultivations of selected strains (P. fluorescens and R. opacus) with depolymerized softwood Kraft lignin (DL).
• Size-exclusion chromatography (SEC) to analyze changes in lignin molecular weight distribution and compound consumption.

Main Results:

• Pseudomonas fluorescens DSM 50090 and Rhodococcus opacus DSM1069 demonstrated the best growth on lignin.
• R. opacus consumed low-molecular weight compounds (0.1-0.4 kDa) in DL, including guaiacol, without significantly altering larger fractions.
• P. fluorescens did not consume low-molecular weight compounds or guaiacol but induced a shift towards lower average molecular weights in the DL.

Conclusions:

• Rhodococcus opacus and Pseudomonas fluorescens are identified as potential microbial candidates for depolymerized lignin bioconversion.
• R. opacus targets low-molecular weight lignin fragments, while P. fluorescens acts on high-molecular weight fragments.
• These findings are relevant for developing strategies for the bioconversion of softwood Kraft lignin.