The growth of motile algae: from plankton blooms to biofuel production

微型藻类是迷人的单细胞微生物，在地球上无处不在。它们在全球生态和生物技术中发挥着至关重要的作用。像植物一样，微藻也是光合作用的，将大气中的碳从二氧化碳固定成碳水化合物。因此，微藻参与全球碳循环，在气候调节中发挥关键作用。微藻的光合作用能力，以及某些物种产生油性化合物的能力，也意味着它们可以作为植物的替代品，作为生物燃料的原料，迫切需要减少碳排放和限制气候变化。尽管最近取得了进展，但有关藻类种群生长的许多信息仍有待发现，这限制了我们控制其生长的能力。事实上，环境中的微藻种群可以爆炸性地生长成水华，从而为环境着色：从池塘的鲜艳绿色到海洋中壮观的蓝绿色或红色浮游生物水华（有些如此广泛，以至于从太空中可以看到！）。这些水华中有许多是良性的，为以微藻为食的生物（从鱼苗到鲸鱼）提供了大量食物。然而，一些微藻物种形成“有害藻华"，由于它们产生的毒素，或由于它们的生长使其他物种挨饿或窒息而有毒。每年，有害藻华不仅杀死大量鱼类，还杀死海洋动物和人类，造成巨大的经济影响。更好地了解藻类生长有助于预测和预防赤潮。它还可以帮助生产微藻生物燃料。含油植物目前用于生物燃料生产，例如油菜籽是制造生物柴油的常见原料。然而，与粮食作物的竞争使植物成为生物燃料的候选者。另一方面，微藻几乎可以在任何地方生长，比植物生长得更快，只利用阳光和回收的工业/农业废物营养素，气体和水。然而，由于生产成本高，目前没有从微藻工业化制造生物燃料。许多微藻物种已经进化出游泳的能力，并使它们的游泳偏向于更好地在水中导航和寻找食物。与细菌共生还提供营养益处，例如必需维生素。偏泳微藻的物理学和共生营养生物学的最新进展尚未应用于游泳微藻种群生长的研究。我们建议对不断增长的游泳微藻种群进行首次系统研究，以考虑游泳的物理学和共生细菌的作用。特别是，使用数学建模和实验相结合，我们的目标是量化有偏见的游泳微藻种群的增长。我们的调查结果将使藻类生长，这将反过来提供可能的解决方案，以控制有害生物和提高微藻生物燃料生产的经济性更全面的了解。

Microscopic algae are fascinating unicellular microorganisms ubiquitous on Earth. They play vital roles in global ecology and biotechnology. Like plants microalgae are photosynthetic, fixing atmospheric carbon from carbon dioxide into carbohydrates. Microalgae thus participate in the global carbon cycle and play a critical role in climate regulation. The photosynthetic ability of microalgae, together with the capacity of some species to produce oily compounds, also means they can be used as an alternative to plants as a feedstock for biofuels, which are urgently required to reduce carbon emissions and limit climate change. In spite of recent advances, much about the growth of algal populations remains to be discovered, which limits our ability to control their growth. Indeed, microalgal populations in the environment can grow explosively into blooms, which colour their environment: from the vivid greens of ponds to the spectacular blue-greens or reds of plankton blooms in the ocean (some so extensive that they are visible from space!). Many of these blooms are benign, providing a bounty for organisms that feed on microalgae (from fish larvae to whales). However, some microalgal species form `harmful algal blooms' (HAB), noxious because of the toxins they produce, or because their growth starves or suffocates other species. Each year HABs kill significant numbers of fish, but also marine animals and people, with substantial economic impact. A better understanding of algal growth could help predict and prevent HABs. It could also help the production of microalgal biofuels. Oily plants are currently used for biofuel production, e.g. rapeseed is a common feedstock to make biodiesel. Competition with food crops, however, makes plants problematic biofuel candidates. Microalgae, on the other hand, grow almost anywhere, faster than plants, using only sunlight and recycled industrial/agricultural waste nutrients, gases and water. However, no biofuel is currently manufactured industrially from microalgae due to high production costs. Many microalgal species have evolved the ability to swim and bias their swimming to better navigate in water and source food. Symbiosis with bacteria also provides nutritional benefits, such as essential vitamins. Recent advances in physics of biased swimming microalgae and the biology of symbiotic nutrition have not yet applied to the study of growth of swimming microalgal populations. We propose to carry out the first systematic study of the growing populations of swimming microalgae to consider both the physics of swimming and the role of symbiotic bacteria. In particular, using a combination of mathematical modelling and experiments we aim to quantify the growth of biased swimming microalgal populations. The results of our investigation will allow a more complete understanding of algal growth, which will in turn provide possible solutions to control HABs and to improve the economics of microalgal biofuel production.