Interactions between phytoplankton and bacterioplankton mediated by volatile organic compounds

动植物之间的交流通常是通过在正常温度下很容易蒸发的分子进行的，称为挥发性有机化合物(VOC)。一些在海洋中产生的VOCs，然后以气体的形式进入大气，已经被认为在气候中扮演着重要的角色。由于海洋微生物既生产又消耗这些化合物，它们会影响表层海洋中挥发性有机化合物的浓度。研究人员发现，光合作用产生的高达20%的碳以VOCs的形式从微小的植物中泄漏出来。这些分子随后被细菌用作碳和能量的来源。这表明，VOCs在海洋环境中的碳流动中可能扮演着比之前认为的更重要的角色。这个项目研究了微小的植物和细菌如何产生和消耗不同的VOCs。它支持俄勒冈州农村地区高中教师在俄勒冈州州立大学科学与数学研究性学习体验(SMILE)项目中的专业发展培训研讨会。SILE的使命是通过增加STEM内容的知识，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职业生涯，缩小服务不足学生的成就差距。该项目还每年举办三次讲习班，培训教师，并让学生参与有关海洋微生物碳循环专题的实践学习活动，如“瓶子里的云”。一名研究生、一名博士后学者和至少六名本科生通过参与研究活动进行培训。现场观测表明，浮游植物产生的挥发性有机化合物(VOC)要么被表层海洋中的浮游细菌迅速消耗，要么排放到大气中。挥发性有机化合物是在阳光灿烂的海洋生态系统中微生物食物网中碳转移的一条未被充分研究的途径，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生物细胞悬浮液中的VOCs，在共培养中，20%的光合碳固定被认为是以VOCs的形式从硅藻转移到SAR11浮游细菌的。其中许多转移的VOC化合物并不是浮游细菌的生长底物。观测到的挥发性有机碳转移的规模和复杂性都令人惊讶。该项目通过对培养物、共培养物和中附着体的对照研究，将这些观察扩展到更大的一组浮游植物和浮游细菌。通过质子转移反应飞行时间质谱仪检测VOC，用同位素标记法测量VOC交换对光合作用速率和细菌产量的影响。浮游植物的挥发性有机化合物的产生是为了响应营养物质驱动的生长速率的变化，并在昼夜循环中识别挥发性有机碳的产生与光合作用代谢和其他细胞过程的关系。这些实验使人们能够更好地了解现场观测，在现场观测中，VOCs的细菌消耗似乎远远超过了VOC的产生，而VOC产生的时间变化从每日到季节的尺度可以导致VOCs在表层海洋中瞬时积累到PM-NM浓度。该项目有助于弥合关于浮游植物产生的VOCs的范围和数量，以及这些化合物在浮游植物代谢中所扮演的角色的知识的显著差距。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.