Collaborative Research: Assessing phosphorus-status in Prochlorococcus through kinetics and molecular approaches in chemostats and natural populations

可能由人类活动引起的全球气候变化正在对海洋产生影响。在北太平洋副热带环流中，由于气候相关的N2固定增加和随后的磷(P)限制，似乎正在发生向原核生物主导的生态系统的域转移。在这个地区，单细胞海洋蓝藻原绿球藻的数量在过去的几十年里一直在增加。目前尚不清楚原绿球藻种群是否受磷限制，或者它们在磷限制条件下是否具有竞争优势。最近有报道称，原绿球藻的HLI基因型在这些磷限制的水域中占主导地位，HLI原绿球藻的浓度很低。对HLI和HLII原绿球藻的磷利用和磷胁迫反应的研究发现，它们在利用有机磷源的能力和碱性磷酸酶活性方面存在显著差异，而基因组比较显示，它们在磷相关基因的补体方面差异不大。这就提出了一个问题，即这两种HL基因型的P生理差异是什么，以及原绿球藻的自然种群是否经历P限制并利用有机P。研究人员将采用生理和遗传方法对培养分离株和自然种群进行研究。这些研究将包括对原绿球藻的无菌HL菌株进行磷限制摄取动力学研究，以确定它们的相对竞争能力，并检测磷限制趋化因子中关键磷相关基因的表达。他们还将开展一项实地研究，通过检查基因型特异性基因表达和自然种群中的群落反应以及p富集瓶实验，确定原绿球藻种群是否以及哪些部分是p限制的。拟议的工作旨在解决一个更大的科学问题的一个方面：什么环境因素调节原绿球藻，世界上营养不良的海洋中最丰富的浮游植物物种？研究人员将在培养和自然种群中检测原绿球藻对磷限制的生理和分子反应。将传统的生理方法与先进的分子技术相结合，可以更好地了解原绿球藻的生态生理和天然原绿球藻种群的基因型特异性生理状态。最终，目的是将群落结构与生理功能以及可能的海洋P循环变化联系起来。该项目将支持两所大学的两名处于学术生涯早期阶段的女研究员、三名研究生和多名本科生的工作。该项目将为USM的本科生提供宝贵的研究和实地经验，USM主要是一所本科院校，主要服务于缅因州南部地区的非传统学生。南加州大学和华盛顿大学之间的思想和技术的交流将通过不断开发新的、基于研究的实验室作业，对两所大学的课程设置内容产生直接影响。

Global climate change, likely caused by human activities, is having an impact on the oceans. In the North Pacific Subtropical Gyre, a domain shift to an ecosystem dominated by prokaryotic organisms appears to be occurring due in part to climate-related increases in N2 fixation and subsequent phosphorus (P)-limitation. In this region, populations of the unicellular marine cyanobacterium Prochlorococcus have been increasing over the last several decades. It is not clear whether Prochlorococcus populations are P-limited or whether they have a competitive advantage under conditions of P limitation. Recently it has been reported that the HLII genotype of Prochlorococcus dominates in these P-limited waters, and HLI Prochlorococcus are present in very low concentrations. Studies on P utilization and P-stress response of axenic HLI and HLII Prochlorococcus isolates revealed significant differences in their ability to utilize organic P sources and in alkaline phosphatase activity, whereas a genomic comparison revealed few differences in their complement of P-related genes. This raises the question of what differentiates the P physiology of these two HL genotypes, and whether natural populations of Prochlorococcus experience P limitation and utilize organic P. The investigators will carry out a study employing physiological and genetic approaches on cultured isolates as well as natural populations. These will include P-limited uptake kinetic studies on axenic HL strains of Prochlorococcus to determine their relative competitive ability and examine expression of key P-related genes in P-limited chemostats. They will also carry out a field study to determine if, and which portions of, the Prochlorococcus populations are P-limited through examination of the genotype-specific gene expression and community response in natural populations and P-enrichment bottle experiments. The proposed work is designed to address one aspect of a larger scientific issue: what environmental factors regulate Prochlorococcus, the most abundant phytoplankton species in the world's oligotrophic oceans? The investigators will examine physiological and molecular responses of Prochlorococcus to P-limitation in cultured and natural populations. This combination of traditional physiological methods with state-of-the-art molecular techniques will allow a better understanding of the ecophysiology of Prochlorococcus and the genotype-specific physiological status of natural Prochlorococcus populations. Ultimately, the intent is to relate community structure to physiological function and possibly to changes in the marine P cycle. The project will support the work of two female investigators in the early stages of their academic careers as well as three graduate students, and multiple undergraduates at both institutions. The project will provide valuable research and field experience to undergraduates at USM, which is primarily an undergraduate institution serving mainly non-traditional students in the Southern Maine region. The cross-fertilization of ideas and techniques between USM and UW will have a direct influence on the content of course offerings at both institutions, through continued development of new, research-based laboratory assignments.