Sustainable Synthesis of Wax Esters from Plant Waste by Bacteria

该项目的目的是从废弃植物材料中生产和提取蜡酯，以取代石油基蜡产品，并作为包装应用中塑料的可持续替代品。蜡是脂肪酸和醇的酯，其可衍生自多种来源。2018年，全球蜡市场的价值超过100亿美元，1增长受到蜡的理想特性的推动，包括防水和耐化学性以及无毒。当时，矿物（石油）蜡占市场的75%，另外20%来自合成蜡（也是化石燃料衍生的），约5%来自动物和植物。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不断增加，导致人们对蜡用于食品包装和储存产生了兴趣。植物来源提供了一个有吸引力的替代方案，因为植物生长期间的光合作用从大气中吸收二氧化碳，将大气中的碳捕获在化学原料中。然而，由于过时的提取程序和缓慢、困难的培养，大量的土地需求和高成本的结合阻止了直接从植物中大规模生产蜡。生物催化、微生物蜡生成是一种更便宜、更可持续的替代方法，使用食品和农业废物流作为原料。贝氏不动杆菌（Acinetobacter baylyi）是已知的蜡酯的天然生产者，因此已经形成了先前对微生物衍生的蜡的研究的起点。合成生物学还允许对细菌进行工程改造以产生不同饱和度和长度的蜡酯，这表明了修饰生物合成途径以确保所需生物产品的受控产生的潜力。这个小组以前的工作集中在从废弃植物材料的厌氧消化中产生挥发性脂肪酸（VFA），这是一个产生甲烷气体的过程。这些VFA可以通过Baylyi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值和底物浓度，将被改变，并评估所产生的蜡的性质。还将测量蜡产率的过程动力学和时间依赖性。将对产量进行量化，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，例如其酸值、碘值和皂化值，将通过已知的文献方法确定，以评估为各种目的产生的蜡的适用性。将探索新的蜡提取方法，以实现最大的产量，最小的能源和溶剂使用。还将使用一系列不同的废弃植物材料来研究原料对蜡的性质和产率的影响。将根据其蜡生产能力和其来源的经济可持续性选择适当的基质。这项工作与EPSRC合成生物学研究领域保持一致，并且福尔斯属于未来制造主题。

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 However, the combination of large land requirements and high costs due to outdated extraction procedures and slow, difficult cultivations prohibit mass wax production directly from plants.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.