EAGER: Iron-Virus Interactions in the Ocean

EAGER：海洋中铁与病毒的相互作用

• 批准号: 1722761
• 负责人: Kristen Buck
• 金额: $ 29.93万
• 依托单位: University of South Florida
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-02-01 至 2020-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1722761&HistoricalAwards=false
• 关键词: EAGER; Iron; Virus; Interactions; Ocean

Iron is an essential micronutrient for phytoplankton that is required for photosynthesis and respiration. Insufficient iron has been shown to limit phytoplankton growth in large regions of the surface ocean, and correspondingly, iron cycling is directly linked to carbon cycling in much of the marine environment. Nearly all iron in seawater (99%) exists as complexes with organic molecules called ligands, which govern the concentration of iron dissolved in the water and the bioavailability of that iron to phytoplankton. However, despite the importance of iron-binding organic ligands, their sources and identities are largely unknown. Viruses, the majority of which are phages (viruses that infect bacteria), are extremely abundant in seawater and are in the same size fraction as dissolved iron. Recent evidence that non-marine phages contain iron as part of their structures has led to the proposal that marine phages may represent a previously overlooked class of organic iron-binding ligands. This project is determining the contribution of marine phages to dissolved iron pools and culture phage-host systems in the laboratory to determine if phages utilize bacterial iron-uptake receptors for infection in the manner of a Trojan horse. As the first study to examine the biogeochemical impact of trace elements contained within the structure of highly abundant marine phage particles, successful completion of the proposed research will be transformative for biological and chemical oceanography and have far-reaching implications for other fields, including human health where iron availability plays an important role in microbial pathogenesis. This project contributes to the multidisciplinary training of a graduate student and postdoctoral researcher. Research results will be disseminated through scientific publications and presentations, and the public will be educated about linkages between viruses and ocean chemistry via a hands-on exhibit for the annual St. Petersburg Science Festival. Building upon evidence from non-marine model systems demonstrating the presence of iron ions in phage tail proteins and phage utilization of cell surface receptors for siderophore-bound iron, this project combines field and laboratory-based experiments to test the following three hypotheses regarding iron-virus interactions in the oceans: (1) Iron incorporated into phage tails originates from bacterial cell reserves, reducing the amount of iron available for remineralization upon lysis; (2) Phages constitute important iron-binding ligands in the oceans, accounting for a substantial portion of organically complexed colloidal dissolved iron; (3) Marine phages compete with siderophore-bound iron for uptake receptors on the bacterial cell surface and use iron in their tails as a Trojan horse for infection. Initial calculations predict that phages could account for up to 70% of the colloidal fraction of organically complexed dissolved iron in the surface ocean; therefore, this project is critical for advancing knowledge of trace-metal cycling as well as phage-host interactions. Additionally, if a portion of the cellular iron thought to be released from bacterial cells for remineralization following lysis is already incorporated into phage tails, then these findings will have significant implications for oceanic biogeochemical models. Through a combination of laboratory-based culture experiments and field sample measurements, this project could reveal the identity of a ubiquitous component of colloidal organic iron-binding ligands, modify the estimates of iron concentrations and species released through viral lysis, and potentially identify a novel receptor type for marine phage that may compete with the acquisition of siderophore-bound iron by host bacteria.

铁是浮游植物光合作用和呼吸所必需的微量元素。研究表明，在海洋表面的大片区域，铁的不足会限制浮游植物的生长，相应地，铁的循环与大部分海洋环境中的碳循环直接相关。海水中几乎所有的铁（99%）都以一种叫做配体的有机分子的复合物的形式存在，配体控制着溶解在水中的铁的浓度以及这些铁对浮游植物的生物利用度。然而，尽管铁结合有机配体的重要性，他们的来源和身份在很大程度上是未知的。病毒，其中大多数是噬菌体（感染细菌的病毒），在海水中非常丰富，与溶解铁的大小相同。最近的证据表明，非海洋噬菌体含有铁作为其结构的一部分，这导致了海洋噬菌体可能代表以前被忽视的一类有机铁结合配体的提议。该项目正在确定海洋噬菌体对溶解铁池和实验室培养噬菌体-宿主系统的贡献，以确定噬菌体是否以特洛伊木马的方式利用细菌铁摄取受体进行感染。作为第一个研究富含海洋噬菌体颗粒结构中所含微量元素的生物地球化学影响的研究，拟议研究的成功完成将对生物和化学海洋学产生革命性影响，并对其他领域产生深远影响，包括人类健康，其中铁的可用性在微生物致病机理中起着重要作用。该项目有助于培养研究生和博士后的多学科人才。研究成果将通过科学出版物和报告传播，并将通过一年一度的圣彼得堡科学节的动手展览向公众宣传病毒与海洋化学之间的联系。基于来自非海洋模型系统的证据，证明了噬菌体尾部蛋白中存在铁离子，以及噬菌体利用细胞表面受体获得铁载体结合的铁，本项目结合现场和实验室实验，测试了关于海洋中铁病毒相互作用的以下三种假设：(1)纳入噬菌体尾部的铁来自细菌细胞储备，减少了裂解时可用于再矿化的铁量；(2)噬菌体是海洋中重要的铁结合配体，占有机络合胶体溶解铁的很大一部分；(3)海洋噬菌体与铁载体结合的铁争夺细菌细胞表面的摄取受体，并利用尾巴上的铁作为感染的特洛伊木马。最初的计算预测，噬菌体可以占到海洋表面有机络合溶解铁的胶体部分的70%；因此，该项目对于推进微量金属循环以及噬菌体-宿主相互作用的知识至关重要。此外，如果一部分被认为是在裂解后从细菌细胞中释放出来用于再矿化的细胞铁已经被纳入噬菌体尾部，那么这些发现将对海洋生物地球化学模型产生重大影响。通过实验室培养实验和现场样品测量相结合，该项目可以揭示胶体有机铁结合配体中普遍存在的成分的身份，修改通过病毒裂解释放的铁浓度和种类的估计，并可能确定一种新的海洋噬菌体受体类型，这种受体可能与宿主细菌获取铁载体结合的铁相竞争。