Research Development Fellowship. Towards biorefineries based on wastes: efficient enzymatic lignin degradation

石油储量的减少和气候变化是未来50-100年社会面临的主要挑战。目前正在开发一些解决方案，其中之一是用液体生物燃料取代化石燃料。生物燃料是通过发酵植物衍生的糖来生产乙醇和丁醇的。生产生物燃料的最简单方法是发酵粮食作物，如甘蔗、谷物、大米或玉米，但含有淀粉的粮食作物生产的工业生物燃料的增加已经导致粮食价格上涨。如果发达国家继续满足对液体运输燃料的需求，而牺牲发展中国家的粮食供应，这就引发了大范围饥饿的幽灵。一种解决方案可能是增加种植含淀粉作物的土地面积。然而，这将减少生物多样性，带来不可避免的环境后果。此外，在为人类提供足够的淡水供应方面已经存在严重问题的情况下，增加作物种植将增加用水量。因此，解决办法是显而易见的：我们必须使用收获粮食作物和加工供人类消费的食物后剩下的废物，而不是使用淀粉作为生产生物燃料的主要原料。我们还必须学会利用我们目前作为垃圾送往垃圾填埋场的材料。最大的问题是，农业和食品垃圾主要由木质纤维素组成，城市垃圾也与包装塑料混合在一起。虽然纤维素已经可以用作生产生物燃料的原料，但木质素和废塑料更难分解成有用的化学物质，除非在恶劣的反应条件和高温下。因此，本项目的目标是开发新的酶法来降解木质素和塑料，这种方法可以在低温下使用环境友好的试剂。我们将使用称为木质素酶的不寻常的酶，这种酶能够产生称为自由基的反应产物。自由基是化学恐怖分子--他们几乎摧毁了他们接触到的任何分子。木质素酶是由木材腐烂真菌产生的，其天然功能是分解木材中的木质素。然而，木质素酶在工业上也被用来粉碎各种分子，包括染料、化学中间体和塑料。这些酶在自然条件下不能很好地工作，因为木质素不溶于水，而且酶不能足够近地有效地粉碎木质素。因此，我们计划用离子液体代替水来使酶和木质素接触。离子液体是盐，但与常见的结晶盐(如氯化钠)不同，它们不能在零度以下的温度下形成适当的晶体。在室温下，它们是液体，具有非常特殊的性质，包括溶解木质素和支持酶活性的能力。因此，离子液体将有助于溶解木质素，酶将其分解形成有用的产品。这将使木质素的降解速度比在水中快得多。在这个项目中，我们将开发新的工艺来分解木质素和其他废弃聚合物，用作生物炼油厂的原料，以生产有用的化学品和燃料。

Dwindling oil reserves and climate change represent major challenges for society over the next 50-100 years. A number of solutions are being developed, one of which is the replacement of fossil fuels with liquid biofuels. Biofuels are produced by fermenting plant-derived sugars to produce ethanol and butanol. The easiest way to produce biofuels is to ferment food crops, such as sugar cane, cereals, rice or maize, but the increase in industrial biofuel production from starch-containing food crops is already leading to increasing food prices. This raises the spectre of widespread starvation if the developed world continues to meet the need for liquid transportation fuels at the expense of food supplies for developing countries. One solution might be to increase the area of land cultivated to produce starch-containing crops. However, this would reduce biodiversity, with the inevitable environmental consequences. Furthermore, increasing crop cultivation would increase water use, at a time when there is already a serious problem with providing enough fresh water for the human population to drink. Therefore, the solution is obvious: instead of using starch as the primary feedstock for biofuel production, we must use waste materials that are left over after harvesting food crops and after processing food for human consumption. We must also learn to make use of materials that we currently send to landfill as rubbish. The big problem is that agricultural and food wastes are composed primarily of lignocellulose, and municipal wastes are also mixed with plastics from packaging. Whilst cellulose can already be used as a feedstock for biofuel production, lignin and waste plastics are much more difficult to break down into useful chemicals except under harsh reaction conditions and at high temperatures. Therefore, the aim of this project is to develop new enzymatic methods to degrade lignin and plastics which will work at low temperatures with environmentally benign reagents. We shall use unusual enzymes called ligninases, which are able to produce reactive reaction products, called free radicals. Free radicals are chemical terrorists - they literally blow apart any molecule that they come into contact with. Ligninases are produced by wood rotting fungi, and their natural function is to break down lignin in wood. However, ligninases are also exploited in industry to smash up all sorts of molecules, including dyes, chemical intermediates and plastics. The enzymes do not work very well under natural conditions because lignin is not soluble in water and the enzymes cannot get close enough to smash the lignin efficiently. Therefore, we plan to use ionic liquids instead of water to bring the enzyme and the lignin into contact. Ionic liquids are salts, but unlike the familiar crystalline salts (e.g. sodium choride), they are unable to form proper crystals except at sub-zero temperatures. At room temperature, they are liquids, and they have very unusual properties, including the ability to dissolve lignin and support enzymatic activity. Therefore, the ionic liquids will help to dissolve the lignin and the enzyme will break it down to form useful products. This will make it possible to degrade lignin much more quickly than in water. In this project, we shall develop new processes to break down lignin and other waste polymers for use as feedstocks in biorefineries to produce useful chemicals and fuels.