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作用所必需的微量营养素。铁不足已被证明限制浮游植物生长在大面积的表层海洋，相应地，铁循环直接与碳循环在许多海洋环境。海水中几乎所有的铁（99%）都以与称为配体的有机分子的复合物的形式存在，这些配体控制着溶解在水中的铁的浓度以及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，其来源和身份在很大程度上是未知的。病毒，其中大部分是细菌（感染细菌的病毒），在海水中非常丰富，并且与溶解的铁具有相同的大小。最近的证据表明，非海洋生物含有铁作为其结构的一部分，导致海洋生物可能代表了以前被忽视的一类有机铁结合配体的建议。该项目正在确定海洋细菌对溶解铁池的贡献，并在实验室中培养噬菌体宿主系统，以确定海洋细菌是否以特洛伊木马的方式利用细菌铁吸收受体进行感染。作为第一个研究高度丰富的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变革性影响，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发病机制中起着重要作用。该项目有助于研究生和博士后研究人员的多学科培训。研究成果将通过科学出版物和介绍会传播，并将通过一年一度的彼得堡科学节的实践展览教育公众了解病毒与海洋化学之间的联系。 该项目以非海洋模型系统的证据为基础，证明噬菌体尾蛋白中存在铁离子，噬菌体利用细胞表面受体与铁载体结合，结合实地和实验室实验，检验关于海洋中铁-病毒相互作用的以下三个假设：（1）掺入噬菌体尾部的铁来源于细菌细胞储备，减少了裂解时可用于再矿化的铁的量;（2）噬菌体是海洋中重要的铁结合配体，占有机络合的胶体溶解铁的很大一部分;（3）海洋细菌与铁载体结合的铁竞争细菌细胞表面的吸收受体，并利用其尾部的铁作为特洛伊木马进行感染。 初步计算预测，在海洋表层有机络合溶解铁的胶体部分中，铁可以占到70%;因此，该项目对于推进痕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，如果一部分细胞铁被认为是从细菌细胞中释放出来的，用于溶解后的再矿化，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的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物种的估计，并可能确定一种新的海洋噬菌体受体类型，可能与宿主细菌竞争收购铁载体结合的铁。