Horizontal gene transfer of cyanobacterial carbon fixing machinery: Implications for the rise of modern atmospheric oxygen

蓝藻固碳机制的水平基因转移：对现代大气氧气上升的影响

• 批准号: NE/Z00019X/1
• 负责人: Richard Puxty
• 金额: $ 112.79万
• 依托单位: University of Warwick
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FZ00019X%2F1
• 关键词: Horizontal; gene; transfer; cyanobacterial; carbon

Much of life on Earth relies on oxygen for aerobic respiration. Indeed, it is thought that mammalian reproductive systems cannot operate at oxygen concentrations much lower than today's 21%. It is therefore vitally important that we understand how oxygen is generated, maintained and consumed. The cycling of oxygen is just one of numerous 'redox-coupled' biogeochemical cycles, whereby the majority of transformations are carried out by biology. For instance, our primordial Earth completely lacked free oxygen, until the evolution of photosynthesis freed it from water more than two billion years ago. The subsequent rise of oxygen concentrations until today has been crucial for the evolution of complex life forms. Yet, this rise has been far from linear. Indeed, for most of Earth's history, oxygen concentration remained at less than one percent of today's value, with geochemical proxies suggesting large and rapid fluctuations in atmospheric oxygen roughly 600 million years ago. It is important that we establish what events catalyse these swings, to predict future habitability. Over geological timescales, oxygen concentration is controlled by three factors: 1) The amount of primary production of the biosphere, 2) The global balance of photosynthesis to aerobic respiration and 3) The rate of burial of carbon-rich organic matter into mostly marine sediments. Roughly 25% of present primary production is carried out by one group of microorganisms, marine cyanobacteria. This group represent the most numerically abundant photosynthetic organisms on Earth. They evolved roughly 650 million years ago, narrowly pre-dating a rapid rise in oxygen concentration, suggesting their distinct physiology could have driven this rise. However, we have no understanding of how this group became so abundant in the marine environment. We recently identified a genetic change that is unique to this group that controls an important aspect of photosynthesis. This genetic change involves cellular machinery, called the carboxysome, which allows carbon fixation to function efficiently. This group of cyanobacteria acquired their carboxysome from distantly related bacteria and it has subsequently been passed to all descendants. Here, we propose that this unique genetic change allows photosynthesis to better operate when nutrients are limiting. We call this the oligotrophy hypothesis. If this genetic change would have allowed these organisms to adapt to oligotrophy, this would have promoted their rapid expansion into the vast Neoproterozoic oceans, which were otherwise devoid of primary producers. The result would have been a large increase in planetary primary productivity and increase in atmospheric oxygen. By combining interdisciplinary approaches, we will test this exciting hypothesis . We will combine 'genetic transplants' of carboxysome genes and cellular modelling to understand their underlying effect on cell physiology. We will use field work to experimentally test selection of trophic status on carboxysome type. We will then integrate this data with evolutionary scenarios of cyanobacteria into geochemical models of the Neoproterozoic oceans to understand if this mechanism could plausibly explain the rise in oxygen supporting complex life. Our findings will have important implications for our understanding of the habitability of life on Earth and the existence of complex life beyond our planet.

地球上的大部分生命都依赖有氧呼吸的氧气。确实，人们认为哺乳动物的生殖系统不能以氧气浓度低于当今的21％低得多。因此，我们了解如何生成，维护和消耗氧气至关重要。氧气的循环只是众多“氧化还原耦合”生物地球化学循环之一，因此，大多数转化都是通过生物学进行的。例如，我们的原始地球完全缺乏自由的氧气，直到光合作用的进化将其从水中释放到了20亿年前。直到今天，氧气浓度的随后升高对于复杂生命形式的演变至关重要。然而，这种上升远非线性。确实，在地球历史的大部分时间里，氧气浓度仍然不到当今价值的百分之一，地球化学代理表明大约6亿年前的大气氧气中大而快速的波动。重要的是，我们必须确定哪些事件催化这些摇摆，以预测未来的可居住性。在地质时间尺度上，氧浓度受三个因素控制：1）生物圈的一级产生量，2）光合作用与有氧呼吸的全球平衡和3）3）富含碳有机物的埋葬率主要是海洋沉积物。目前大约25％的初级生产是由一组微生物海洋蓝细菌进行的。该组代表了地球上数值最丰富的光合生物。他们大约在6.5亿年前进化出来，缩小了氧气浓度的迅速增长，这表明它们的独特生理可能会驱动这一上升。但是，我们对这一群体在海洋环境中如何变得如此丰富。我们最近确定了该群体独有的遗传变化，该变化控制着光合作用的重要方面。这种遗传变化涉及称为羧化体的细胞机制，该机械使碳固定能够有效发挥作用。这组蓝细菌从遥远相关的细菌中获取了羧化体，随后已传递给所有后代。在这里，我们建议这种独特的遗传变化可以使光合作用在限制营养时更好地运行。我们将其称为寡聚假说。如果这种遗传变化将使这些生物适应寡头萎缩，那么这将促进它们的快速扩张到庞大的新元古代海洋中，这些海洋否则没有主要生产者。结果将是行星原发性生产力和大气中氧气增加的大幅提高。通过结合跨学科方法，我们将检验这一令人兴奋的假设。我们将结合羧化体基因的“遗传移植”和细胞建模，以了解它们对细胞生理的潜在影响。我们将使用现场工作来实验测试羧化体类型的营养状态。然后，我们将将这些数据与蓝细菌的进化情景整合到新元古代海洋的地球化学模型中，以了解这种机制是否可以显然可以解释氧气支持复杂寿命的升高。我们的发现将对我们对地球生命的居住能力以及地球以外的复杂生命的存在具有重要意义。