Microbial engineering for catabolism of lignin-derived aromatic compounds

Abstract

Lignin is found in nature as one of the most abundant biopolymers. The large amounts of lignin generated as a by-product or waste from mainly pulp and paper industry have great potential as a source of renewable (aromatic) carbon and could be applied for production of platform chemicals in the proposed circular economy/biorefinery concept. Due to the heterogenous lignin polymer structure, its degradation and depolymerization are challenging, however, when achieved, the degradation stream holds great potential due to the high number of heterogeneous molecules. Nonetheless, the large number of aromatic compounds found in the stream is recognised as a challenge. In this study, the successful engineering of a microbial cell-factory for utilizing lignin-derived aromatic compounds has been described. A pathway was identified for catabolising aromatic compounds and this pathway together with some additional reactions have been expressed in a suitable platform strain. A new generation of strains has been constructed for catabolising lignin-derived aromatic compounds and characterised by measuring growth and extracellular metabolites by UHPLC from high cell density aerobic cultivations.

Popular Abstract

There are many different types of plants on our planet and they are all built up of three major components which are cellulose, hemicellulose and lignin. Cellulose is commonly used as a raw material for producing mostly paper and paper products, but a portion of it has also been used for textile production. Hemicellulose, on the other hand, is a smaller compound than cellulose and the development of new methods for using hemicellulose as raw material for food, pharmaceutical and chemical industries is increasing. Lignin has been described as the “glue” holding cellulose and hemicellulose together. All these components provide the plants with strength, stability and structure. Lignocellulose, which is the name used for the complex of the lignin, hemicellulose and cellulose forming the cell walls in plants, is of high abundance in nature and has gained popularity in science and research for its potential as a renewable energy source. One example is biofuels production, which can lead to the replacement of the use of fossil fuels.

When plant biomass from, for example, wood is processed to produce pulp and paper, only the cellulose and part of the hemicellulose is used. The lignin has a very complex aromatic structure and is generated as a waste product after it has gone through some chemical processes. The chemical processes usually change the lignin structure, so this lignin that is generated is named technical lignin because of its slight differences to the lignin found in nature. However, the amount of technical lignin coming out as waste from the pulp and paper industry is large because of the large quantities of plant mass processed. The production companies themselves use this technical lignin for energy by burning it. The stream of lignin, however, holds great potential because when lignin is broken down into a mixture of smaller aromatic molecules, these molecules can be used and converted into other valuable products. To separate this mixture of smaller molecules is a challenge, because of the high costs, possible impurities, use of organic solvents etc. Therefore, in this project, we developed and characterised microorganisms able to consume some of the aromatic compounds derived from lignin and produce building blocks for other useful products.

Some organisms in nature, mostly fungi and some bacteria, can degrade lignin. For example, when trees in the forest have been cut and the wood is left, there are some fungi (moulds, mushrooms) that are able to grow on it and eventually degrade it. They have mechanisms which allow them to get nutrients by degrading the wood and the lignin as well. A mechanism was found, more suitably called a metabolic pathway or a collection of sequential enzymatic reactions, common in some of the organisms from nature, for converting aromatic compounds into building blocks. The organisms from nature are in general difficult to use for industrial applications, therefore we chose an established model organism that is safe and has already been used in industry. In this project, the metabolic pathway that was found was introduced into our microorganism by state-of-the-art genetic engineering methods. The pathway was built into the microorganism by adding genes that express enzymes for specific reactions stepwise and several combinations were made to see how each gene influences the cell. The microorganisms were grown and fed with specific mixtures containing lignin-derived aromatics and an analytical method was used to see if there was any consumption of the aromatics or production of any new compounds. A microbial cell was successfully engineered to consume some aromatic compounds coming from lignin. Some hurdles still exist, and several modifications and optimisations need to be made in the future for actual application of these microorganisms in the industry, however, this work is of high relevance.

• author: Muratovska, Nina
• supervisor: Daniel Brink
• organization: Applied Microbiology; Biotechnology
• alternative title: Mikrobiell genteknik för katabolism av aromatiska föreningar från lignin
• course: KMBM01 20181
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: applied microbiology, teknisk mikrobiologi
• language: English
• id: 8950555
• date added to LUP: 2018-06-18 15:43:48
• date last changed: 2018-06-18 15:43:48