Using cold adapted photobionts to improve photosynthesis in economically important organisms

据预测，到2050年，全球人口数量将上升到96亿（Bradshaw和Brook， 2014）。再加上全球平均气温上升和气候变化，对全球粮食安全构成重大风险。世界上许多地方目前的农业做法都很陈旧，显示出优化的潜力；防止大量砍伐森林，提高用水效率。优化的一个解决方案可以通过基因工程的应用。Rubisco的活性是植物生物化学的一个领域，它被强调为植物生产力的一个重要瓶颈，因此需要优化。这种酶在光合生物中起着固定二氧化碳的主要催化剂的作用。因此，Rubisco是地球上最丰富的蛋白质，每个人有5kg的Rubisco （Phillips and Milo, 2009）。然而，它在催化速率和特异性方面都是低效的。它在35亿年前在富含二氧化碳的大气中进化，当时不需要特异性（Bracher et al., 2017）。这是由地球历史上两次重大的氧合事件进行的，这使得Rubisco的快速进化成为必要，相对于O2，增加了CO2的特异性（Erb和Zarzycki， 2018）。尽管如此，特异性仍然是Rubisco作用的低效率，因为该酶经常催化氧与RuBP的结合。这导致形成3-磷酸甘油酸酯（3-PGA）和2-磷酸乙醇酸酯（2-PG），其中2-PG对植物有毒。因此，它必须经过叶绿体、过氧化物酶体和线粒体的高能量代谢过程才能从2-PG中回收RuBP。在Rubisco的催化下，CO2与RuBP交替结合，形成两个3-PGA分子；可用于进一步合成糖以供生长的产品（Bracher et al., 2017）。Rubisco动力学的两个组成部分经常相互关联，导致特异性和催化速率之间的权衡，其中一个的增加会对另一个产生负面影响。相反，在高纬度海洋环境中，由于不同的吸收动力学，CO2浓度相对于O2增加。这与在许多海洋光自养生物中发现的碳捕获机制（CCM）的存在相结合，假设可以消除对Rubisco特异性的严格要求。这反过来又会在低温下产生高于预期的催化速率（催化速率随着温度的降低呈指数下降）（Feller和Gerday， 2003）。因此，研究这一相对未被充分研究的冷适应海洋生物分支，主要由藻类物种组成，可能会产生潜在的新的和有益的Rubisco变异。这个概念可以通过生物工程转化为重要的经济作物。这将主要通过以下步骤实现：收集和培养本研究最初将需要培养从培养库和原始冰川样品中获得的嗜冷藻类菌株。2. 测序随后将对Rubisco基因进行测序，以确定藻类Rubisco与其他温带生物的遗传变异程度。动力学分析测序将与动力学分析和高通量Rubisco定量一起进行。这将有助于解释极地藻类有效吸收碳的进化机制。高档藻类生物反应器是工业的一个组成部分。由于其酶在低温下具有活性，因此具有很大的生物技术应用潜力。因此，研究的最后一步是优化培养基和硬件，以大规模培养生物学上有趣的菌株。通过增长模型的应用。

It is predicted that global population numbers will rise to 9.6 billion by the year 2050 (Bradshaw and Brook, 2014). This coupled with the rise of average global temperatures and climatic change poses a significant risk to global food security. Current agricultural practices in many parts of the world are archaic demonstrating the potential for optimisation; preventing significant deforestation and increasing water use efficiency. One solution for optimisation can be through the application of genetic engineering.An area of plant biochemistry that has been highlighted as a significant bottle neck in plant productivity and therefore in need of optimisation, is the activity of Rubisco. This is the enzyme that acts as the primary catalyst for CO2 fixation in photosynthetic organisms. As a result Rubisco is the most abundant protein on earth with 5kg of Rubisco for every human (Phillips and Milo, 2009). However it is both inefficient in terms of catalytic rate and specificity. It evolved in a CO2 rich atmosphere 3.5 billion years ago, where specificity was not a requirement (Bracher et al., 2017). This was proceeded by two great oxygenation events in earth's history which necessitated the rapidevolution of Rubisco, increasing specificity for CO2 relative to O2 (Erb and Zarzycki, 2018). None the less, specificity remains an inefficiency in Rubisco action as the enzyme will frequently catalyse the binding of oxygen with RuBP. This leads to the formation of 3-phosphoglycerate (3-PGA) and 2-phosphoglycolate (2-PG) of which 2-PG is toxic to the plant. Therefore it must undergo a highly energetic metabolic process through the chloroplast, peroxisomes and mitochondria to recycle RuBP from 2-PG. Alternatively binding of CO2 with RuBP, catalysed by Rubisco, results in the formation of two 3-PGA molecules; products that can be used to synthesise further sugars for growth (Bracher et al., 2017). The two components of Rubisco kinetics are often interlinked leading to a trade-off between specificity and catalytic rate with an increase in one negatively impacting the other.In contrast, within high latitude marine environments concentrations of CO2 increase relative to O2 due to differing absorption kinetics. This coupled with the presence of a carbon capture mechanism (CCM), found in many marine photoautotrophs is hypothesised to remove the stringent requirement for Rubisco specificity. This in turn would give rise to higher than expected catalytic rates at low temperatures (catalytic rate falls exponentially with decreasing temperature) (Feller and Gerday, 2003). Therefore investigating this relatively understudied clade of cold adapted marine organisms, largely consisting of algae species, may give rise to potentially novel and beneficial variations of Rubisco. A concept that can be bioengineered into economically important crops. This will be achieved primarily through the following steps:1. Collection and CultureThis study will initially require the culturing of psychrophilic algal strains obtained from culture banks and raw glacial samples. 2. SequencingThis will be followed by the subsequent sequencing of the Rubisco genes to determine the degree of genetic variation of the algal Rubisco from other temperate organisms.3. Kinetic assaysSequencing will be performed in conjunction with kinetic assays and high throughput Rubisco quantification. This should elucidate to the evolutionary mechanism that allows polar algal populations to assimilate carbon efficiently.4. UpscaleAlgal bioreactors are a constituent part of industry. Psychrophilic algae have great potential for biotechnological application, with enzymes being active at low temperatures. Therefore the final step of the study is to optimise media and hardware to culture biologically interesting strains on a large scale. Through the application of growth models.