Aggregation of Marine Picoplankton

海洋浮游植物是生活在海洋日照带的微小藻类。它们在通过光合作用从大气中吸收二氧化碳方面发挥着重要作用，类似于陆地上的植物，是海洋食物网的基础。然而，海洋浮游植物不是将这种有机碳储存在叶组织和根中，而是被浮游动物捕食，或者死亡，然后以聚集体的形式下沉到日照带外，也被称为“海洋雪”。这些颗粒不仅将细胞中含有的有机碳输出到深海，还可以作为生活在深海中的动物和细菌的食物。这些浮游植物中有相当一部分非常小，是已知的所有生物中最微小的之一。这些极小的单元格被认为在海洋雪的形成和下沉中并没有发挥重要作用；然而，最近的发现挑战了这一观点。这个项目将调查这些最小的浮游植物是如何促成雨水从阳光照耀的表面向深海下沉的颗粒。这项研究很重要，因为在一些最大的开阔海域，这些微小的细胞主导着浮游植物群落，而较大的浮游生物非常稀少。该项目通过实验室和野外站的工作相结合，将揭示这些微小的浮游植物细胞如何形成聚集体，最终使它们能够以“海洋雪”的形式下沉。该项目还为亚利桑那州立大学的本科生提供了独特的机会，让他们在海洋研究方面获得经验。亚利桑那州立大学是一所内陆公立大学。该项目将用于培养一名博士生，一名攻读加速BS-MS项目的MS学生，以及8-10名本科生/学期，进行一项独特的、基于探究的学习努力，称为微生物教育培训和推广(导师)。这些本科生还将参加亚利桑那州立大学S生命科学学院的本科生研究项目，该项目旨在增加少数族裔对科学的参与。他们还将在该项目的基础上为开发网络和课堂材料作出贡献，这些材料随后将通过与获奖的亚利桑那州立大学赞助的Ask A生物学家K-12网站的伙伴关系分发。海洋“生物碳泵”是通过光合作用将溶解的无机碳转化为颗粒和溶解有机碳并随后将其输出到深水，是海洋吸收大气碳的重要驱动因素。传统的观点认为，海洋中的生物碳泵是由浮游植物的大型矿物压载细胞组成的大型集合体(海洋雪)或粪便颗粒的下沉。然而，来自对颗粒物的现场调查、捕捉器研究和模型研究的最新证据表明，微米级浮游植物，如微蓝细菌和微真核生物，可对颗粒物的下沉作出重大贡献。这些微米大小的细胞下沉背后的具体机制仍然难以捉摸，因为这些细胞太小，不能自己下沉，而且中游动物可能无法吞噬单个细胞。有趣的是，研究人员最近的研究表明，普遍存在的聚球藻能够形成聚集体，并以与海洋雪相当的速度下沉。他们发现聚球藻聚集体的基质是由透明的胞外聚合物颗粒(TEP)组成的，在营养有限的培养条件下，TEP的产量得到了提高。与粘土的相互作用和异养菌的存在也提高了聚集和下沉速度。这项研究的目的是进一步调查实验室中其他常见微浮游动物的聚集以及在一个少营养的开阔海洋站点--百慕大大西洋时间序列站点(BATS)--在自然环境中发生的聚集。最终，这个项目将增加和完善我们对最小的浮游植物在聚集和下沉中所起作用的理解--这些信息对于理解海洋中的碳循环过程至关重要。

Marine phytoplankton are microscopic algae that live in the sunlit zone of the ocean. They play an important role in the uptake of carbon dioxide from the atmosphere through photosynthesis, similar to what plants do on land, and are the basis of the marine food web. However, instead of storing this organic carbon in leaf tissue and roots, marine phytoplankton are grazed by planktonic animals, or die and subsequently sink out of the sunlit zone in the form of aggregates, also called "Marine Snow". These particles not only export the organic carbon contained in their cells to the deep ocean, but also serve as food for animals and bacteria that live in the deep. A considerable portion of these phytoplankton are extremely small, among the tiniest of all organisms known. These extremely small cells have not been thought to play an important role in the formation and sinking of marine snow; however, recent findings challenge this view. This project will investigate how the smallest of these phytoplankton contribute to the rain of sinking particles from the sunlit surface to the deep ocean. This research is important because, in some of the largest expanses of the open oceans, these minute cells dominate the phytoplankton community, and larger plankton organisms are very sparse. The project, through a combination of work in the laboratory and at a field station, will shed light on how these tiny phytoplankton cells make aggregates, which ultimately enable them to sink as "Marine Snow". The project also provides unique opportunities for undergraduate students at Arizona State University, a land-locked public university, to gain experience in working with marine research. The project will serve to educate one PhD student, one MS student in an accelerated BS-MS program, and 8-10 undergraduate students/semester in a unique, inquiry based learning effort termed Microbial EducatioN Training and OutReach (MENTOR). The undergraduate students will also participate in Arizona State University (ASU)'s School of Life Sciences, Undergraduate Research Program (SOLUR), which seeks to increase the participation of minorities in science. They will also contribute towards developing web and classroom materials, based on this project, which will then be distributed through a partnership with the award-winning ASU-sponsored Ask A Biologist K-12 web site.The oceanic "biological carbon pump", the photosynthetically mediated transformation of dissolved inorganic carbon into particulate and dissolved organic carbon and its subsequent export to deep water, functions as a significant driver of atmospheric carbon uptake by the oceans. The traditional view of the biological carbon pump in the ocean is that of sinking of large aggregates (marine snow) or fecal pellets, which are made up of large, mineral ballasted cells of phytoplankton. However, recent evidence, stemming from in situ investigations of particulate matter, trap studies and modelling studies, have shown that micron-sized phytoplankton such as picocyanobacteria as well as picoeukaryotes can contribute significantly to the sinking of particulate matter. The specific mechanisms behind the sinking of these micrometer sized cells remain elusive as the cells are too small to sink on their own, and mesozooplankton is likely unable to ingest single cells. Intriguingly, recent research by the investigators has shown that the ubiquitous picocyanobacteria Synechococcus are able to form aggregates and sink at velocities comparable to those of marine snow. They found that the matrix of the Synechococcus aggregates was made of Transparent Exopolymeric Particles (TEP), and that TEP production was enhanced under nutrient limited culture conditions. Interaction with clays and presence of heterotrophic bacteria also enhanced aggregation and sinking velocity. This study aims to further investigate aggregation of other common picoplankton in the laboratory and aggregation occurring in natural settings at an oligotrophic open ocean site, the Bermuda Atlantic Time-series Site (BATS). Ultimately, this project will increase and refine our understanding of the role of the smallest phytoplankton in aggregation and sinking - information vital to understanding carbon cycling processes in the oceans.