Molecular basis of algal-bacterial interactions and its implications for industrial cultivation of microalgae

世界正面临着一个相当大的挑战，那就是用基于生物燃料等清洁能源技术的经济来补充并最终取代以化石燃料为基础的经济。目前，商业上可用的生物燃料（如生物乙醇和生物柴油）是从玉米和大豆等农作物中提取的。然而，在利用宝贵的农业用地生产生物燃料作物以及这些技术的可持续性和能源平衡方面存在重大关切。一种潜在的替代生物燃料来源是微藻——一种不需要肥沃土地种植的水生光合生物；生长速度比植物快得多，并且可以积累大量的高能量化合物，如油。此外，这种水生养殖可以与工业排放的二氧化碳和富含营养的废水等废物相结合，从而利用这些废物促进藻类生长。然而，工业规模的微藻生物燃料种植面临着相当大的挑战，不仅在技术可行性方面，而且在经济和实现净正能量平衡方面。特别是，尽管在称为光生物反应器的封闭管状系统中可以实现适当菌株的最佳生产率，但建造和操作这些设施所需的能量远远大于提取燃料所需的能量。相比之下，与化石柴油相比，开放式回旋池的增长通常会节省能源。另一方面，露天池塘受到细菌、病毒或竞争藻类污染的风险很大。因此，作物保护是一个必须解决的关键问题，以使藻类有效和富有成效的商业化。我们已经发现了微藻和细菌之间的相互作用，这可能为这种作物保护提供一种手段。超过一半的微藻需要维生素B12才能生长，它们可以从细菌中获得维生素B12，以换取光合作用产生的糖。我们已经找到了一种可能的解释，解释了为什么这么多藻类需要这种维生素——似乎是失去了一种叫做METE的特殊基因，使藻类从一个有效的“狩猎采集者”（如果有B12的话）变成了一个“自给自足的农民”（需要培养细菌来确保这种维生素的适当供应）。这表明，这两种生物一定有相互传递信号的方式，而且这种生活方式也有一些优势，因为它如此普遍。在这个项目中，我们将测试我们的假设，并确定藻类和细菌在共培养中一起生长是否会影响藻类细胞中燃料分子的生产力，以及它是否会防止入侵物种的污染。我们还将使用几种分子方法来识别可能参与这种相互作用的基因和蛋白质，特别是藻类细胞对B12的吸收。

The World is faced with the considerable challenge of supplementing, and ultimately replacing, its fossil fuel-based economy with one based on clean energy technologies such as biofuels. Currently, commercially available biofuels (e.g. bioethanol and biodiesel) are derived from crop plants such as maize and soybean. However, there are major concerns regarding both the use of valuable agricultural land for production of biofuel crops, and the sustainability and energy balance of such technologies. A potential alternative source of biofuels is microalgae - aquatic photosynthetic organisms that do not require fertile land for cultivation; grow considerably faster than plants, and which can accumulate significant quantities of high-energy compounds such as oils. Furthermore, such aquatic cultivation could be coupled to waste streams such as CO2 output from industry and nutrient-rich effluent, thereby using this waste to promote algal growth. However, industrial-scale cultivation of microalgae for biofuels faces considerable challenges, not just in terms of technical feasibility, but also in terms of economics and achieving a net positive energy balance. In particular, although the best rates of productivity of suitable strains are achieved in enclosed tubular systems, called photobioreactors, the energy requirement for building and operating these facilities is much greater than that in the fuel that is extracted. In contrast, growth in open raceway ponds generally results in energy savings compared to fossil-derived diesel. On the other hand, open ponds are at great risk from contamination by bacteria, viruses or competing algae. Crop protection is therefore a key issue that must be addressed to allow effective and productive commercialisation of algae. We have discovered an interaction between microalgae and bacteria that might provide a means to assist in this crop protection. Over half of all species of microalgae require vitamin B12 for growth - and they can obtain it from bacteria, in return for sugars made from photosynthesis. We have identified a possible explanation for why so many algae need this vitamin - it appears that loss of a particular gene, called METE, changes an alga from being effectively a 'hunter-gatherer', using B12 if it is available, to a 'subsistence farmer', needing to cultivate bacteria to ensure a proper supply of this vitamin. This suggests that there must be ways in which the two organisms signal to one another, and also that there is some advantage to this lifestyle, since it is so prevalent. In this project we will test our hypothesis, and determine if the growth of algae and bacteria together in cocultures affect the productivity of fuel molecules in the algal cells, and if it prevents contamination by invasive species. We will also use several molecular approaches to identify genes and proteins that might be involved in this interaction, in particular in the uptake of B12 by the algal cells.