Interactions between phytoplankton and bacterioplankton mediated by volatile organic compounds

植物和动物之间的交流通常是通过在常温下容易蒸发的分子进行的，这种分子被称为挥发性有机化合物（VOCs）。一些挥发性有机化合物在海洋中产生，然后以气体的形式进入大气，在气候中起着重要作用。由于海洋微生物既产生又消耗这些化合物，它们会影响海洋表面挥发性有机化合物的浓度。研究人员发现，光合作用产生的碳中有多达20%以挥发性有机化合物的形式从微观植物中泄漏出来。这些分子随后被细菌用作碳和能量的来源。这表明，挥发性有机化合物在海洋环境中的碳流中扮演的角色可能比之前认为的更重要。该项目研究微观植物和细菌如何产生和消耗不同的挥发性有机化合物。它支持俄勒冈州立大学科学与数学研究性学习经验（SMILE）项目中俄勒冈州农村地区高中教师的专业发展培训讲习班。SMILE的使命是通过增加他们的STEM内容知识，为他们在高等教育中取得成功做好准备，并激励他们追求STEM职业，从而缩小服务不足的学生的成就差距。该项目还每年举办三次研讨会，培训教师和学生参与海洋微生物碳循环的实践学习活动，如“瓶中的云”。研究生1名，博士后1名，本科研究人员至少6名。实地观察表明，浮游植物产生的挥发性有机化合物要么被海洋表层的浮游细菌迅速消耗，要么被排放到大气中。在整个阳光照射的海洋生态系统中，挥发性有机化合物是微生物食物网中碳转移的一个尚未得到充分研究的途径，因为这些化合物需要专门的检测方法。利用一种新的系统来研究活浮游细胞悬浮液中的挥发性有机化合物，在共培养中，20%的光合作用碳固定被发现作为挥发性有机化合物从硅藻转移到SAR11浮游细菌。许多这些转移的挥发性有机化合物不知道是浮游细菌的生长基质。观察到的VOC转移的大小和复杂性都令人惊讶。本项目通过对培养物、共培养物和中生态系统的对照研究，将这些观察结果扩展到更大范围的浮游植物和浮游细菌。挥发性有机化合物通过质子转移反应飞行时间质谱法检测，同位素标记用于测量挥发性有机化合物交换对光合作用和细菌生产速率的影响。浮游植物挥发性有机化合物的产生是根据营养驱动的生长速率变化而测量的，并通过昼夜循环来辨别挥发性有机化合物的产生与光合代谢和其他细胞过程的关系。这些实验使我们能够更好地理解实地观测，其中细菌对挥发性有机化合物的消耗可能明显超过产生，而挥发性有机化合物产生的时间变化在日常到季节性尺度上可能导致挥发性有机化合物在海洋表面短暂积累到pM-nM浓度。该项目有助于缩小对浮游植物产生的挥发性有机化合物的范围和数量以及这些化合物在浮游植物代谢中所起作用的认识差距。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Communication amongst plants and animals often occurs through molecules that readily evaporate at normal temperatures, called volatile organic compounds (VOCs). Some VOCs that are produced in the ocean and then enter the atmosphere as gases have been seen to play an important role in climate. Since marine microbes both produce and consume these compounds they affect the concentration of VOCs in the surface ocean. The investigators found that as much as 20% of the carbon resulting from photosynthesis leaked out of microscopic plants in the form of VOCs. These molecules were then used by bacteria as a source of carbon and energy. This suggests that VOCs may play a more important role in the flow of carbon in the marine environment than previously thought. This project examines how microscopic plants and bacteria produce and consume different VOCs. It supports professional development training workshops for Oregon high school teachers from rural areas in OSU’s Science & Math Investigative Learning Experiences (SMILE) program. SMILE’s mission is to close the achievement gap for underserved students by increasing their STEM-content knowledge, preparing them to succeed in higher education, and inspiring them to pursue STEM careers. This project also contributes to three workshops per year, training teachers and engaging students with hands-on learning activities on the topic of Carbon Cycling by Marine Microorganisms such as “Clouds in a Bottle”. One graduate student, one post-doctoral scholar, and at least six undergraduate researchers are being trained by participating in research activities. Field observations suggest that volatile organic compounds (VOCs) produced by phytoplankton are either rapidly consumed by bacterioplankton in the surface ocean or emitted into the atmosphere. VOCs are an understudied path for carbon transfer in microbial food webs throughout sunlit marine ecosystems because these compounds require specialized detection methods. Using a new system to study VOCs in suspensions of live plankton cells, 20% of photosynthetic carbon fixation was seen to be transferred as VOCs from a diatom to SAR11 bacterioplankton in co-cultures. Many of these transferred VOC compounds were not known to be growth substrates for bacterioplankton. Both the magnitude and complexity of the observed VOC transfer were surprising. This project extends these observations to a larger set of phytoplankton and bacterioplankton through controlled studies of cultures, co-cultures, and mesocosms. VOC are detected via proton transfer reaction time-of-flight mass spectrometry and isotopic labeling is used to measure the impact of VOC exchange on rates of photosynthesis and bacterial production. VOC production by phytoplankton is measured in response to nutrient-driven variation in growth rates, and over day-night cycles to discern the relationship of VOC production to photosynthetic metabolism and other cellular processes. These experiments enable a better understanding of field observations, in which bacterial consumption of VOCs can appear to significantly outpace production, while temporal variability in VOC production across daily to seasonal scales can cause VOCs to accumulate transiently to pM-nM concentrations in the surface ocean. This project contributes to close the significant gap in knowledge about the range and quantity of VOCs produced by phytoplankton, and about the roles played by these compounds in phytoplankton metabolism.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.