Using cold adapted photobionts to improve photosynthesis in economically important organisms

据预测，到2050年，全球人口数量将增至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。世界许多地区目前的农业做法都是陈旧的，显示了优化的潜力；防止大量砍伐森林和提高水的利用效率。一种优化的解决方案可以通过应用基因工程来解决。在植物生物化学领域，Rubisco的活性一直被强调为植物生产力的一个重要瓶颈，因此需要优化。这是一种酶，在光合作用的有机体中充当固定二氧化碳的主要催化剂。因此，Rubisco是地球上最丰富的蛋白质，每个人摄入5公斤Rubisco(Phillips和Milo，2009)。然而，就催化效率和特异性而言，它都是低效的。它是在35亿年前富含二氧化碳的大气中进化的，在那里，专一性并不是一个要求(Bracher等人，2017年)。这是由地球历史上两次重大的氧化事件引发的，这两次事件需要Rubisco的快速分解，增加了二氧化碳相对于O2的专一性(Erb和Zarzycki，2018)。然而，由于Rubisco酶经常催化氧与RuBP的结合，因此在Rubisco作用中，特异性仍然是无效的。这会导致3-磷酸甘油酸酯(3-PGA)和2-磷酸乙三酸酯(2-PG)的形成，其中2-PG对植物是有毒的。因此，它必须经历一个高能量的代谢过程，通过叶绿体、过氧酶体和线粒体来回收2-PG中的RuBP。在Rubisco的催化下，二氧化碳与RuBP的交替结合导致两个3-PGA分子的形成；这些分子可用于合成更多的糖以供生长(Bracher等人，2017年)。Rubisco动力学的两个组成部分通常是相互关联的，导致在特异性和催化速率之间进行权衡，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，由于吸收动力学的不同，二氧化碳的浓度相对于氧气的浓度会增加。再加上在许多海洋光自养生物中发现的碳捕获机制(CCM)的存在，假设消除了对Rubisco特异性的严格要求。这反过来会导致低温下的催化速率高于预期(催化速率随着温度的降低呈指数下降)(Feller和Gerday，2003)。因此，研究这种主要由藻类组成的适应寒冷的海洋生物分支相对较少的研究，可能会产生潜在的新的和有益的Rubisco变异。这个概念可以被生物工程改造成具有重要经济价值的作物。这将主要通过以下步骤实现：1.收集和培养本研究最初将要求培养从培养库和原始冰川样品中获得的嗜冷藻类菌株。2.测序这之后将对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。这应该有助于阐明极地藻类种群高效吸收碳的进化机制。UpscaleAlga生物反应器是工业的组成部分。嗜冷藻具有很大的生物技术应用潜力，其酶在低温下具有活性。因此，这项研究的最后一步是优化培养基和硬件，以大规模培养具有生物学意义的菌株。通过应用增长模型。

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.