Biodegradation of alkaline lignin by Bacillus ligniniphilus L1

Daochen Zhu,Bin Yang,Wei-Jun Qian,Changxiao Xie,Weimin Zhang,Peipei Zhang,Jianzhong Sun

doi:10.1186/s13068-017-0735-y

Abstract

BackgroundLignin is the most abundant aromatic biopolymer in the biosphere and it comprises up to 30% of plant biomass. Although lignin is the most recalcitrant component of the plant cell wall, still there are microorganisms able to decompose it or degrade it. Fungi are recognized as the most widely used microbes for lignin degradation. However, bacteria have also been known to be able to utilize lignin as a carbon or energy source. Bacillus ligniniphilus L1 was selected in this study due to its capability to utilize alkaline lignin as a single carbon or energy source and its excellent ability to survive in extreme environments.ResultsTo investigate the aromatic metabolites of strain L1 decomposing alkaline lignin, GC–MS analysis was performed and fifteen single phenol ring aromatic compounds were identified. The dominant absorption peak included phenylacetic acid, 4-hydroxy-benzoicacid, and vanillic acid with the highest proportion of metabolites resulting in 42%. Comparison proteomic analysis was carried out for further study showed that approximately 1447 kinds of proteins were produced, 141 of which were at least twofold up-regulated with alkaline lignin as the single carbon source. The up-regulated proteins contents different categories in the biological functions of protein including lignin degradation, ABC transport system, environmental response factors, protein synthesis, assembly, etc.ConclusionsGC–MS analysis showed that alkaline lignin degradation of strain L1 produced 15 kinds of aromatic compounds. Comparison proteomic data and metabolic analysis showed that to ensure the degradation of lignin and growth of strain L1, multiple aspects of cells metabolism including transporter, environmental response factors, and protein synthesis were enhanced. Based on genome and proteomic analysis, at least four kinds of lignin degradation pathway might be present in strain L1, including a Gentisate pathway, the benzoic acid pathway and the β-ketoadipate pathway. The study provides an important basis for lignin degradation by bacteria.

Highlights

Lignin is the most abundant aromatic biopolymer in the biosphere and it comprises up to 30% of plant biomass
Growth of strain L1 on the lignin medium To investigate the growth of strain L1 with lignin or glucose as the carbon source, cells were incubated in mineral medium (MM63) medium with lignin and glucose or only lignin as the carbon source at 30 °C or 50 °C for 7 days with pH 9
When the incubation temperature increased from 30 to 50 °C, the stationary phase was extended from 72 to 144 h in the batch incubation with glucose and lignin as the carbon source. This is because when glucose was exhausted after 48 h incubation (Fig. 1), the lignin provided energy as carbon source to support the growth of strain L1 at 50 °C

Summary

Introduction

Lignin is the most abundant aromatic biopolymer in the biosphere and it comprises up to 30% of plant biomass. Bacteria have been known to be able to utilize lignin as a carbon or energy source. The pathways of lignin degradation were different in different bacteria, some bacteria contain oxidative enzymes to modify lignin by hydroxylation or demethylation, such as cytochrome P450 monooxygenases (P450s), dye-decolorizing peroxidase (DyP), laccase, manganese superoxide dismutase [17,18,19]. Some bacteria such as Rhodococcus jostii RHA1 used the β-ketoadipate pathway (β-KAP) to degrade the lignin in the absence of hydrogen peroxide [20]. The other branch is catechol branch, which converts catechol, generated from various aromatic hydrocarbons, amino aromatics, and lignin monomers to β-KAP [22]

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