Photoheterotrophy in unicellular cyanobacteria: ecological drivers and significance for marine biogeochemistry

题目：单细胞蓝藻的光异养：海洋生物地球化学的生态驱动因素及其意义单细胞蓝藻是开放海洋初级生产和碳输出的主要贡献者。它们在控制养分有效性方面也起着重要作用。这些微生物收集光能的能力有益于一系列生理功能，但光对其代谢（除了光合作用）的影响知之甚少且存在争议。本项目将研究光在单细胞蓝藻吸收有机基质（碳和营养物质）中的作用，并阐明光异养的重要性。这些生物吸收有机化合物的能力及其和光和营养物质的调节将为海洋中单细胞蓝藻的生态成功提供额外的提示。拟议的工作将包括在西南太平洋进行实地实验，并辅以在与生态有关的蓝藻的受控培养中进行的实验室实验。该研究将采用创新的方法，包括针对单个蓝藻的单细胞分析和分子工具，并评估它们对光的反应，以同化有机基质。该研究项目将有助于加深对微生物对光照和养分梯度的适应以及这些适应在海洋栖息地元素循环中所起作用的理解。本项目将支持一名早期职业女性研究者。研究人员将对本科生和当地高中生进行研究技术培训和指导。该项目的研究结果将通过开放获取出版物传达给科学家。我们将制作一部录象片，记录这次科学巡弋，并总结拟议研究的主要发现，供公众广泛观看。因此，这些活动将涉及广泛的受众，包括相当一部分代表性不足的群体。单细胞蓝藻栖息在海洋表层（一般150米深），利用太阳能来争夺有限的可用营养物质。因此，它们不仅可以利用光能进行光合作用，还可以利用光能增强它们对溶解有机化合物的代谢。然而，光在有机化合物（包括碳和营养物质）吸收中的作用以及光异养的重要性仍然知之甚少。本研究旨在探讨单细胞蓝藻原绿球菌（Prochlorococcus）和聚藻球菌（Synechococcus）和光异养的生态驱动因素和意义，这两种细菌是海洋中数量最多的初级生产菌群，鳄鱼属（Crocosphaera）是重要的固氮生物。该建议认为，适应特定的光照条件必须塑造海洋中微生物群之间资源的时空分配。沿着西南太平洋西-东样带的实地实验将涵盖一系列营养条件和蓝藻丰度。放射性底物培养结合流式细胞术、细胞分选和微放射自显影与催化报告细胞沉积荧光原位杂交（MICRO-CARD-FISH）将允许从非色素浮游细菌中分离单细胞蓝藻，并评估它们对不同有机底物摄取的光响应。这些实验将辅以实验室试验，控制培养的无菌菌株代表不同生态相关的蓝藻功能群。最后，我们将利用代表性菌株WH8501的基因组序列定位葡萄糖代谢相关基因的原位表达，测试重要的固氮动物watsonii对葡萄糖的摄食能力。

Title: Photoheterotrophy in Unicellular Cyanobacteria: Ecological Drivers and Significance for Marine BiogeochemistryUnicellular cyanobacteria are major contributors to primary production and carbon export in the open ocean. They also play an important role in the control of nutrient availability. The ability of these microbes to harvest light energy benefits a range of physiological functions, but the effect of light on their metabolism (other than for photosynthesis) is poorly known and controversial. This project will investigate the role of light in uptake of organic substrates (carbon and nutrients) by unicellular cyanobacteria and elucidate the importance of photoheterotrophy. The ability of these organisms to assimilate organic compounds and its modulation by light and nutrients will provide additional hints about the ecological success of unicellular cyanobacteria in the ocean. The proposed work will involve field experiments in the southwest Pacific Ocean, complemented by laboratory experiments in controlled cultures of ecologically relevant cyanobacteria. The study will employ innovative methods, including single cell assays and molecular tools that target individual cyanobacteria and evaluate their response to light for the assimilation of organic substrates. This research project will lead to an increased understanding of the microbial adaptations to light and nutrient gradients and the role these adaptations play in elemental cycling in oceanic habitats. This project will support an early career female investigator. Both undergraduate students and local high school students will be trained in research techniques and mentored by the investigator. Findings resulting from this project will be communicated to scientists through open-access publications. A video documenting the scientific cruise and summarizing the major discoveries of the proposed research will be produced and be widely accessible to the public. These activities will thus reach a broad audience including a significant fraction of underrepresented groups.Unicellular cyanobacteria inhabit the surface ocean (generally 150 m deep), and use solar energy to compete for a limited supply of available nutrients. Therefore, they are expected to utilize light energy not only for photosynthesis but also to enhance their metabolism of dissolved organic compounds. Yet, the role of light in the uptake of organic compounds (both carbon and nutrients) and the importance of photoheterotrophy are still poorly understood. This proposal seeks to investigate the ecological drivers and significance of photoheterotrophy in the unicellular cyanobacteria Prochlorococcus and Synechococcus, the most abundant groups of primary producers in the ocean, and Crocosphaera an important nitrogen fixing organism. This proposal argues that adaptations to specific light regimes must shape spatiotemporal partitioning of resources among microbial groups in the ocean. Field experiments along a west-east transect in the southwest Pacific Ocean will cover a range of nutrient conditions and cyanobacterial abundances. Radioactive substrate incubations combined with flow cytometry cell sorting and microautoradiography paired to catalyzed reporter deposition fluorescence in situ hybridization (MICRO-CARD-FISH) will allow the separation of unicellular cyanobacteria from non-pigmented bacterioplankton and evaluation of their response to light for the uptake of different organic substrates. These experiments will be complemented by laboratory tests in controlled cultures of axenic strains representative of different ecologically relevant functional groups of cyanobacteria. Lastly, the capacity of the important nitrogen fixer Crocosphaera watsonii to feed on glucose will be tested, taking advantage of the sequenced genome of the representative strain WH8501 in targeting the expression of genes involved in glucose metabolism in situ.