Photosynthesis and genome evolution of cyanobacteria from polar environments

蓝藻是唯一能够进行氧合光合作用的细菌。它们塑造了地球数十亿年来的生物地球化学循环和生物多样性。蓝藻是世界性的，但它们在极端栖息地特别成功。特别是在极地淡水生态系统中，它们形成了以蓝藻为主的复杂微生物群落，是重要的初级生产者，推动了食物网和碳循环。然而，光合作用对极地生境的适应仍然知之甚少。在这些栖息地，低温往往伴随着辐照度的极端波动。冰架上的浅融水池普遍存在强光和紫外线辐射。相比之下，在常年被冰覆盖的湖泊底部，只有一小部分表面辐照度通过冰传输。这表明蓝藻具有极大的适应挑战条件的光合作用的能力。指导这种适应的基本原理不仅可以为生物技术应用设计更健壮或更有弹性的菌株提供洞察力，可以转化为真核藻类和农作物，还可以提供关于生物可塑性的见解，这种可塑性使我们的地球在漫长的不断变化的历史中能够承受氧气光合作用。该项目的目的是通过适应性实验室进化实验，在生理和基因组水平上实时表征蓝藻如何适应恶劣的环境条件。学生将在实验室中培养南极蓝藻，以评估它们在极端光照条件下的适应性和光合作用表现，如极低或极高强度、不同的紫外线辐射水平，以及结合温度变化。选定的南极菌株种群将逐渐适应良好的实验室条件，以在一段时间内释放选择性压力。同时，与南极分离株相比，实验室蓝藻将逐渐适应类似极地的严酷条件和它们的适应性。基因组将被测序，遗传变化将与光合作用性能相关。NHM还收集了10,000多个蓝藻的历史样本，包括一个多世纪前斯科特船长的英国南极探险期间收集的样本，这些样本将使用古老的DNA提取方法进行测序，并与蓝藻分离株和南极洲现有的元基因组数据进行比较。

Cyanobacteria are the only bacteria capable of oxygenic photosynthesis. They have shaped Earth's biogeochemical cycles and biodiversity for billions of years. Cyanobacteria are cosmopolitan, but they are especially successful in extreme habitats. Particularly, in polar freshwater ecosystems where they form complex cyanobacteria-dominated microbial mat communities and are important primary producers, driving food webs and carbon cycling.However, adaptation of photosynthesis to polar habitats remains poorly understood. In these habitats, low temperatures are often accompanied by extreme fluctuations in irradiance. High light intensities and ultraviolet radiation are common for shallow meltwater ponds on the ice shelves. In contrast, only a tiny fraction of the surface irradiance is transmitted through the ice at the bottom of perennially ice-covered lakes. This suggests that cyanobacteria have a tremendous capacity to acclimate photosynthesis to challenging conditions. The fundamental principles that govern such adaptations can provide insights not only into engineering more robust or resilient strains for biotech applications, translatable toeukaryotic algae and crops, but also on the biological plasticity that enables the endurance of oxygenic photosynthesis over the long history of our constantly changing planet.The aim of the project is to characterize in real time, at a physiological and genomic level, how photosynthesis in cyanobacteria acclimates to harsh environmental conditions using adaptive laboratory evolution experiments.The student will grow Antarctic cyanobacteria in the laboratory to evaluate their fitness and photosynthetic performance under extreme light conditions such as very low or high intensities, different UV radiation levels, and in combination with changes in temperature. Selected populations of Antarctic strains will be gradually acclimated to benign laboratory conditions as to release selective pressures over a period of time. In parallel, laboratorycyanobacteria will be gradually acclimated to harsh polar-like conditions and their fitness compared to Antarctic isolates. Genomes will be sequenced, and genetic changes will be correlated with photosynthetic performance.The NHM also has collections of over 10,000 historic samples of cyanobacteria, including those collected during Captain Scott's British Antarctic Expedition over a century ago that will be sequenced using ancient DNA extraction approaches and compared with cyanobacteria isolates and available metagenome data from Antarctica.