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

职务名称：单细胞蓝细菌的光合异养：海洋生物地球化学的生态驱动力和意义单细胞蓝细菌是开放海洋初级生产和碳输出的主要贡献者。它们在控制养分供应方面也发挥着重要作用。这些微生物收集光能的能力有益于一系列生理功能，但光对它们的新陈代谢（除了光合作用）的影响知之甚少，也存在争议。本研究将探讨光在单细胞蓝细菌吸收有机基质（碳和养分）中的作用，并阐明光异养的重要性。这些生物同化有机化合物的能力及其受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更多的线索。拟议的工作将包括在西南太平洋进行实地实验，并辅之以在控制下培养与生态有关的蓝细菌的实验室实验。该研究将采用创新的方法，包括单细胞测定和分子工具，以单个蓝藻为目标，并评估它们对光的反应，以同化有机底物。该研究项目将导致对微生物对光和营养梯度的适应以及这些适应在海洋栖息地元素循环中的作用的更多理解。该项目将支持一名早期职业女性调查员。本科生和当地高中生都将接受研究技术培训，并由研究人员指导。该项目的研究结果将通过开放获取的出版物传达给科学家。将制作一个录像，记录科学航行并概述拟议研究的主要发现，并向公众广泛提供。因此，这些活动将触及广泛的受众，包括很大一部分代表性不足的群体。单细胞蓝细菌栖息在海洋表面（通常150米深），并利用太阳能竞争有限的可用养分供应。因此，它们不仅可以利用光能进行光合作用，还可以利用光能促进溶解有机化合物的代谢。然而，光在有机化合物（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。该提案旨在研究单细胞蓝藻原绿球藻和聚球藻中光合异养的生态驱动因素和意义，原绿球藻和聚球藻是海洋中最丰富的初级生产者群体，而Crocosphaera是一种重要的固氮生物。这一建议认为，适应特定的光制度必须塑造时空的海洋微生物群体之间的资源分配。在西南太平洋沿沿着东西向的样带进行的实地实验将涵盖一系列营养条件和蓝藻丰度。放射性底物孵育结合流式细胞术细胞分选和microautoradiography配对催化报告沉积荧光原位杂交（MICRO-CARD-FISH）将允许从非色素浮游细菌的单细胞蓝藻分离和评价其对光的响应吸收不同的有机底物。这些实验将得到实验室试验的补充，在控制培养物中代表不同生态相关功能组的蓝藻菌纯菌株。最后，将利用代表性菌株WH 8501的测序基因组，在原位靶向参与葡萄糖代谢的基因的表达，测试重要的固氮菌Crocosphaera watsonii以葡萄糖为食的能力。

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.