EAGER: Iron-Virus Interactions in the Ocean

铁是浮游植物必需的微量营养素，是光合作用和呼吸作用所必需的。铁不足已被证明限制了海洋表面大片区域的浮游植物生长，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%)都以被称为配位体的有机分子的络合物的形式存在，这些配位体控制着水中溶解的铁的浓度以及这些铁对浮游植物的生物有效性。然而，尽管铁结合的有机配体很重要，但它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)，在海水中极其丰富，与溶解的铁的大小相同。最近有证据表明，非海洋噬菌体的结构中含有铁，这导致了海洋噬菌体可能代表了一类以前被忽视的有机铁结合配体。该项目正在实验室中确定海洋噬菌体对溶解铁池和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。作为第一个研究高度丰富的海洋噬菌体颗粒结构中所包含的微量元素的生物地球化学影响的研究，这项拟议的研究的成功完成将对生物和化学海洋学产生变革，并对其他领域，包括在微生物发病机制中铁的可获得性起重要作用的人类健康具有深远的影响。该项目对研究生和博士后研究人员的多学科培养做出了贡献。研究成果将通过科学出版物和演示文稿传播，并将通过一年一度的圣彼得堡科学节的动手展览，教育公众有关病毒和海洋化学之间的联系。基于来自非海洋模式系统的证据，表明噬菌体尾部蛋白中存在铁离子，以及噬菌体表面受体对铁载体结合的铁的利用，该项目结合了现场和实验室的实验，以检验关于海洋中铁与病毒相互作用的以下三个假说：(1)进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，占有机胶体溶解铁的很大一部分；(3)海洋噬菌体与铁载体结合，竞争细菌细胞表面的铁摄取受体，并利用尾巴中的铁作为感染的特洛伊木马。初步计算预测，噬菌体可能占表层海洋中有机络合溶解铁的胶体分数的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，如果被认为是在裂解后从细菌细胞中释放出来进行再矿化的细胞铁的一部分已经被并入噬菌体尾巴中，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的结合，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物种的估计，并有可能确定一种新的海洋噬菌体受体类型，它可能与宿主细菌获取铁载体结合的铁竞争。

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.