Photosynthesis and genome evolution of cyanobacteria from polar environments

蓝藻是唯一能够进行含氧光合作用的细菌。数十亿年来，它们塑造了地球的生物地球化学循环和生物多样性。蓝藻是世界性的，但它们在极端的栖息地尤其成功。特别是在极地淡水生态系统中，它们形成了复杂的蓝藻主导的微生物席群落，是重要的初级生产者，推动食物网和碳循环。然而，光合作用对极地栖息地的适应仍然知之甚少。在这些栖息地，低温常常伴随着辐照度的极端波动。高光强和紫外线辐射在冰架上的浅融水池塘中很常见。相比之下，只有很小一部分的表面辐射通过常年被冰覆盖的湖泊底部的冰传播。这表明蓝藻有一个巨大的能力来适应光合作用的挑战条件。控制这种适应的基本原理不仅可以为生物技术应用提供更强大或更有弹性的菌株，可转化为真核藻类和作物，而且还可以为生物可塑性提供见解，使氧气光合作用在我们不断变化的星球的漫长历史中持久存在。该项目的目的是实时表征，在生理和基因组水平上，如何在蓝藻光合作用适应苛刻的环境条件使用适应性实验室进化实验。该学生将在实验室培养南极蓝藻，以评估它们在极端光照条件下的适应性和光合作用性能，如极低或高强度、不同的紫外线辐射水平，以及结合温度变化。南极菌株的选定种群将逐渐适应良好的实验室条件，以便在一段时间内释放选择压力。与此同时，实验室蓝藻将逐渐适应恶劣的极地条件和它们的适应性与南极分离物相比。基因组将被测序，基因变化将与光合作用表现相关联。NHM还收集了超过10,000个蓝藻细菌的历史样本，包括一个多世纪前斯科特船长在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，并与来自南极洲的蓝藻细菌分离物和可用的宏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.