Dataset Information

Visualizing Adsorption of Cyanophage P-SSP7 onto Marine Prochlorococcus.

ABSTRACT: Marine cyanobacteria perform roughly a quarter of global carbon fixation, and cyanophages that infect them liberate some of this carbon during infection and cell lysis. Studies of the cyanobacterium Prochlorococcus MED4 and its associated cyanophage P-SSP7 have revealed complex gene expression dynamics once infection has begun, but the initial cyanophage-host interactions remain poorly understood. Here, we used single particle cryo-electron tomography (cryo-ET) to investigate cyanophage-host interactions in this model system, based on 170 cyanophage-to-host adsorption events. Subtomogram classification and averaging revealed three main conformations characterized by different angles between the phage tail and the cell surface. Namely, phage tails were (i) parallel to, (ii) ~45 degrees to, or (iii) perpendicular to the cell surface. Furthermore, different conformations of phage tail fibers correlated with the aforementioned orientations of the tails. We also observed density beyond the tail tip in vertically-oriented phages that had penetrated the cell wall, capturing the final stage of adsorption. Together, our data provide a quantitative characterization of the orientation of phages as they adsorb onto cells, and suggest that cyanophages that abut their cellular targets are only transiently in the "perpendicular" orientation required for successful infection.

SUBMITTER: Murata K

PROVIDER: S-EPMC5345008 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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Visualizing Adsorption of Cyanophage P-SSP7 onto Marine Prochlorococcus.

Murata Kazuyoshi K Zhang Qinfen Q Gerardo Galaz-Montoya Jesús J Fu Caroline C Coleman Maureen L ML Osburne Marcia S MS Schmid Michael F MF Sullivan Matthew B MB Chisholm Sallie W SW Chiu Wah W

Scientific reports 20170310

Marine cyanobacteria perform roughly a quarter of global carbon fixation, and cyanophages that infect them liberate some of this carbon during infection and cell lysis. Studies of the cyanobacterium Prochlorococcus MED4 and its associated cyanophage P-SSP7 have revealed complex gene expression dynamics once infection has begun, but the initial cyanophage-host interactions remain poorly understood. Here, we used single particle cryo-electron tomography (cryo-ET) to investigate cyanophage-host int ...[more]

PMID: 28281671

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Project description:The oceanic cyanobacteria Prochlorococcus are globally important, ecologically diverse primary producers. It is thought that their viruses (phages) mediate population sizes and affect the evolutionary trajectories of their hosts. Here we present an analysis of genomes from three Prochlorococcus phages: a podovirus and two myoviruses. The morphology, overall genome features, and gene content of these phages suggest that they are quite similar to T7-like (P-SSP7) and T4-like (P-SSM2 and P-SSM4) phages. Using the existing phage taxonomic framework as a guideline, we examined genome sequences to establish "core" genes for each phage group. We found the podovirus contained 15 of 26 core T7-like genes and the two myoviruses contained 43 and 42 of 75 core T4-like genes. In addition to these core genes, each genome contains a significant number of "cyanobacterial" genes, i.e., genes with significant best BLAST hits to genes found in cyanobacteria. Some of these, we speculate, represent "signature" cyanophage genes. For example, all three phage genomes contain photosynthetic genes (psbA, hliP) that are thought to help maintain host photosynthetic activity during infection, as well as an aldolase family gene (talC) that could facilitate alternative routes of carbon metabolism during infection. The podovirus genome also contains an integrase gene (int) and other features that suggest it is capable of integrating into its host. If indeed it is, this would be unprecedented among cultured T7-like phages or marine cyanophages and would have significant evolutionary and ecological implications for phage and host. Further, both myoviruses contain phosphate-inducible genes (phoH and pstS) that are likely to be important for phage and host responses to phosphate stress, a commonly limiting nutrient in marine systems. Thus, these marine cyanophages appear to be variations of two well-known phages-T7 and T4-but contain genes that, if functional, reflect adaptations for infection of photosynthetic hosts in low-nutrient oceanic environments.

Project description:Cyanophage infecting the marine cyanobacteria Prochlorococcus and Synechococcus require light and host photosystem activity for optimal reproduction. Many cyanophages encode multiple photosynthetic electron transport (PET) proteins, which are presumed to maintain electron flow and produce ATP and NADPH for nucleotide biosynthesis and phage genome replication. However, evidence suggests phage augment NADPH production via the pentose phosphate pathway (PPP), thus calling into question the need for NADPH production by PET. Genes implicated in cyclic PET have since been identified in cyanophage genomes. It remains an open question which mode of PET, cyclic or linear, predominates in infected cyanobacteria, and thus whether the balance is towards producing ATP or NADPH. We sequenced transcriptomes of a cyanophage (P-HM2) and its host (Prochlorococcus MED4) throughout infection in the light or in the dark, and analyzed these data in the context of phage replication and metabolite measurements. Infection was robust in the light, but phage were not produced in the dark. Host gene transcripts encoding high-light inducible proteins and two terminal oxidases (plastoquinol terminal oxidase and cytochrome c oxidase)-implicated in protecting the photosynthetic membrane from light stress-were the most enriched in light but not dark infection. Among the most diminished transcripts in both light and dark infection was ferredoxin-NADP+ reductase (FNR), which uses the electron acceptor NADP+ to generate NADPH in linear photosynthesis. The phage gene for CP12, which putatively inhibits the Calvin cycle enzyme that receives NADPH from FNR, was highly expressed in light infection. Therefore, both PET production of NADPH and its consumption by carbon fixation are putatively repressed during phage infection in light. Transcriptomic evidence is thus consistent with cyclic photophosphorylation using oxygen as the terminal electron acceptor as the dominant mode of PET under infection, with ATP from PET and NADPH from the PPP producing the energy and reducing equivalents for phage nucleotide biosynthesis and replication.

Project description:Prochlorococcus cyanobacteria grow in diurnal rhythms driven by diel cycles. Their ecology depends on light, nutrients, and top-down mortality processes, including lysis by viruses. Cyanophage, viruses that infect cyanobacteria, are also impacted by light. For example, the extracellular viability and intracellular infection kinetics of some cyanophage vary between light and dark conditions. Nonetheless, it remains unclear whether light-dependent viral life history traits scale up to influence population-level dynamics. Here, we examined the impact of diel forcing on both cellular- and population-scale dynamics in multiple Prochlorococcus-phage systems. To do so, we developed a light-driven population model, including both cellular growth and viral infection dynamics. We then tested the model against measurements of experimental infection dynamics with diel forcing to examine the extent to which population level changes in both viral and host abundances could be explained by light-dependent life history traits. Model-data integration reveals that light-dependent adsorption can improve fits to population dynamics for some virus-host pairs. However, light-dependent variation alone does not fully explain realized host and virus population dynamics. Instead, we show evidence consistent with lysis saturation at relatively high virus-to-cell ratios. Altogether, our study represents a quantitative approach to integrate mechanistic models to reconcile Prochlorococcus-virus dynamics spanning cellular-to-population scales.IMPORTANCE The cyanobacterium Prochlorococcus is an essential member of global ocean ecosystems. Light rhythms drive Prochlorococcus photosynthesis, ecology, and interactions with potentially lethal viruses. At present, the impact of light on Prochlorococcus-virus interactions is not well understood. Here, we analyzed Prochlorococcus and virus population dynamics with a light-driven population model and compared our results with experimental data. Our approach revealed that light profoundly drives both cellular- and population-level dynamics for some host-virus systems. However, we also found that additional mechanisms, including lysis saturation, are required to explain observed host-virus dynamics at the population scale. This study provides the basis for future work to understand the intertwined fates of Prochlorococcus and associated viruses in the surface ocean.

Dataset Information

Visualizing Adsorption of Cyanophage P-SSP7 onto Marine Prochlorococcus.

Publications

Visualizing Adsorption of Cyanophage P-SSP7 onto Marine Prochlorococcus.

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