Sustainable Synthesis of Wax Esters from Plant Waste by Bacteria

该项目的目的是从废弃的植物材料中生产和提取蜡酯，以取代石油基蜡产品，并在包装应用中作为塑料的可持续替代品。蜡是脂肪酸和醇的酯，可以从各种来源获得。2018年，全球石蜡市场价值超过100亿美元，1增长是由石蜡的理想特性推动的，包括耐水性、耐化学性和无毒性。目前，矿物(石油)蜡占市场份额的75%，另外20%来自合成蜡(也来自化石燃料)，约5%来自天然动植物。1然而，随着社会逐渐摆脱对化石燃料的依赖，必须考虑化学原料的替代碳来源。目前蜡的主要用途是化妆品、个人护理产品、润滑剂和涂料，但对塑料替代品的需求日益增长，导致了人们对用于食品包装和储存的蜡的兴趣。植物来源提供了一个有吸引力的替代方案，因为植物生长过程中的光合作用从大气中吸收二氧化碳，将大气中的碳捕获到化学原料中。然而，由于开采程序过时，加上种植缓慢而困难，所需的土地面积大，成本高，这些因素都阻碍了直接从植物中大规模生产石蜡。生物催化、微生物产生蜡是一种更便宜、更可持续的替代方案，使用食物和农业废弃物作为原料。贝利不动杆菌是已知的蜡酯的天然生产者，因此形成了以前对微生物来源的蜡的研究的起点。合成生物学还允许对细菌进行工程，以生产不同饱和度和长度的蜡酯，展示了修改生物合成途径以确保所需生物产品的受控生成的潜力。该小组之前的工作重点是从废弃植物材料的厌氧消化中产生挥发性脂肪酸(VFAS)，否则这个过程会产生甲烷气体。这些VFA可以被贝利不动杆菌转化为蜡，这是一种以前没有尝试过的新方法。细菌生长的物理因素，包括温度、pH和底物浓度，将会有所不同，并对所产生的蜡的性质进行评估。还将测量蜡产率的过程动力学和时间依赖性。产量将被量化，并分析蜡的基本物理性质，如熔点和粘度。蜡的常见化学性质，如酸、碘和皂化值，将通过已知的文献方法来确定，以评估产生的蜡是否适合各种目的。将探索新的蜡提取方法，以最小的能源和溶剂使用实现最大的产量。还将使用一系列不同的废旧植物材料，研究原料对石蜡性能和产量的影响。将根据蜡的生产能力和来源的经济可持续性来选择合适的基质。这项工作与EPSRC合成生物学研究领域保持一致，属于制造未来的主题。

The aim of this project is to produce and extract wax esters from waste plant material, to replace petroleum based wax products and as sustainable alternatives to plastic in packaging applications. Waxes are esters of fatty acids and alcohols that can be derived from a variety of sources. In 2018 the global wax market was valued at over $10 billion,1 with growth driven by the desirable properties of waxes, including water and chemical resistance and non-toxicity. At this time, mineral (petroleum) waxes accounted for 75% of the market, with a further 20% from synthetic waxes (also fossil fuel derived) and around 5% naturally sourced from animals and plants.1 However, as society moves away from its dependence on fossil fuels, alternative carbon sources for chemical feedstocks must be considered. Current major uses of waxes are cosmetics, personal care products, lubricants and coatings, but increasing demand for alternatives to plastics has led to interest in wax for food packaging and storage. Plant sources offer an attractive alternative, as photosynthesis during plant growth takes in CO2 from the atmosphere, trapping atmospheric carbon in chemical feedstocks. However, the combination of large land requirements and high costs due to outdated extraction procedures and slow, difficult cultivations prohibit mass wax production directly from plants. Biocatalytic, microbial wax generation is a cheaper, more sustainable alternative, with using food and agricultural waste streams as feedstocks. The bacteria Acinetobacter baylyi is a known natural producer of wax esters, and hence has formed the starting point for previous investigations into microbe derived waxes. Synthetic biology also allows the engineering of bacteria to produce wax esters of varying saturation degree and length, demonstrating the potential for modifying biosynthetic pathways to ensure the controlled generation of the desired bioproduct. Previous work by this group has focussed on the generation of volatile fatty acids (VFAs) from the anaerobic digestion of waste plant material, a process which otherwise produces methane gas. These VFAs can be transformed into wax by Acinetobacter baylyi, a novel process not attempted previously. Physical factors of bacterial growth, including temperature, pH and concentration of substrate, will be varied and the properties of the waxes produced assessed. Process kinetics and time dependency of the wax yields will also be measured. Yields will be quantified, and the basic physical properties of the waxes, such as melting point and viscosity, analysed. Common chemical properties of waxes, such as their acid, iodine and saponification values, will be determined through known literature methods to assess the suitability of waxes generated for a variety of purposes. Novel extraction methods for the waxes produced will be explored to achieve maximum yields with minimal energy and solvent use. The effect of feedstock on wax properties and yield will also be investigated, using a range of different waste plant material. Appropriate substrates will be chosen based upon both their wax production capabilities and the economic sustainability of their source. This work is aligned with the EPSRC Synthetic Biology research area and falls within the Manufacturing the Future theme.