Microbes drive ecosystems and their viruses manipulate these processes, yet the importance of tidal functioning on the estuarine viruses and microbes remains poorly elucidated. Here, an integrative investigation on tidal patterns in viral and microbial communities and their inherent interactions over an entire spring-neap tidal cycle was conducted along a macrotidal subtropical estuary. The viral and microbial abundances oscillated significantly over the tidal cycle with relatively higher abundances observed at spring tide compared to neap tide. The distinct tidal dynamic patterns in bacterial production and community composition were tightly associated with the variations in viral infection, production and decay, revealing the tide-driven interactions between viruses and microbes. Concurrent with the higher viral decay but lower bacterial abundance and inhibited bacterial metabolism during the neap tide, lower gross viral production was coupled with a synchronous switching from viral lytic to lysogenic infection induced by the loss of viral infection efficiency and the transition from marine to freshwater bacterial populations triggered by tidal mixing. Our results highlighted the major tidal impact on the microbial dynamics through virus-host interactions, with cascading effects, neglected so far, on estuarine biogeochemical cycles.

The unicellular picocyanobacterium Prochlorococcus is the numerically dominant phytoplankton in the oligotrophic ocean, contributing to the vast majority of marine primary production. Prochlorococcus releases a significant fraction of fixed organic matter into the surrounding environment and supports a vital portion of heterotrophic bacterial activity. Viral lysis is an important biomass loss process of Prochlorococcus .

Marine viruses are major drivers of global biogeochemical cycles and energy fluxes, yet the importance of viral impacts on the succession and diversity of the bacterial community remains largely unexplored. Here, we explored viral life strategy and its potential effect on the bacterial community by experimental incubations of eutrophic coastal waters under lysogen-induced and non-induced treatments. The lysogen-induced treatment showed relatively constant viral and bacterial abundances, lytic and lysogenic viral production throughout the experimental period, together with the progressive declines in not only the relative abundances for SAR11, Rhodobacteraceae, Alteromonadaceae, and SAR86 but the bacterial community diversity. Conversely, the non-induced treatment observed the marked variation in the abundances of viruses, bacteria and cells with high nucleic acid content over the time course of incubation, which was congruent with the drastic shift in lytic and lysogenic viral production as well as the succession of bacterial community. Our results supported the hypotheses that a high level of lysogeny would occur with the increasing density of bacteria with rapid growth rate, which may contribute to a relatively lower host community diversity, whereas the lysogeny to lysis switching would fuel growth opportunities for less-active or initially rare bacterial taxa and generate a more diverse bacterial community. Altogether, the present study underscored the crucial regulatory role of the viral lysis-lysogeny pattern in bacterial community dynamics, composition and diversity, highlighting the viral impact on the microbial food web and biogeochemical processes.

Bacteriophages substantially contribute to bacterial mortality in the ocean and play critical roles in global biogeochemical processes. Alteromonas is a ubiquitous bacterial genus in global tropical and temperate waters, which can cross-protect marine cyanobacteria and thus has important ecological benefits. However, little is known about the biological and ecological features of Alteromonas phages (alterophages). Here, we describe a novel alterophage vB_AmeP-R8W (R8W), which belongs to the Autographiviridae family and infects the deep-clade Alteromonas mediterranea. R8W has an equidistant and icosahedral head (65 ± 1 nm in diameter) and a short tail (12 ± 2 nm in length). The genome size of R8W is 48,825 bp, with a G + C content of 40.55%. R8W possesses three putative auxiliary metabolic genes encoding proteins involved in nucleotide metabolism and DNA binding: thymidylate synthase, nucleoside triphosphate pyrophosphohydrolase, and PhoB. R8W has a rapid lytic cycle with a burst size of 88 plaque-forming units/cell. Notably, R8W has a wide host range, such that it can infect 35 Alteromonas strains; it exhibits a strong specificity for strains isolated from deep waters. R8W has two specific receptor binding proteins and a compatible holin–endolysin system, which contribute to its wide host range. The isolation of R8W will contribute to the understanding of alterophage evolution, as well as the phage–host interactions and ecological importance of alterophages.

Virioplankton are a key component of the marine biosphere in maintaining diversity of microorganisms and stabilizing ecosystems. They also contribute greatly to nutrient cycles/cycling by releasing organic matter after lysis of hosts. In this study, we constructed the first global viral oceanography database (gVOD) by collecting 10 931 viral abundance (VA) data and 727 viral production (VP) data, along with host and relevant oceanographic parameters when available. Most VA data were obtained in the North Atlantic (32 %) and North Pacific (29 %) oceans, while the southeast Pacific and Indian oceans were quite undersampled. The VA in the global ocean was $\mathrm{1.17}(\pm \mathrm{3.31})\times {\mathrm{10}}^{\mathrm{7}}$ particles mL⁻¹. The lytic and lysogenic VP in the global ocean was $\mathrm{9.87}(\pm \mathrm{24.16})\times {\mathrm{10}}^{\mathrm{5}}$ and $\mathrm{2.53}(\pm \mathrm{8.64})\times {\mathrm{10}}^{\mathrm{5}}$ $\mathrm{particles}{\mathrm{mL}}^{-\mathrm{1}}{\mathrm{h}}^{-\mathrm{1}}$ , respectively. Average VA in coastal oceans was higher than that in surface open oceans ($\mathrm{3.61}(\pm \mathrm{6.30})\times {\mathrm{10}}^{\mathrm{7}}$ versus $\mathrm{0.73}(\pm \mathrm{1.24})\times {\mathrm{10}}^{\mathrm{7}}$ particles mL⁻¹), while average VP in coastal and surface open oceans was close. Vertically, VA, lytic VP and lysogenic VP deceased from surface to deep oceans by about 1 order of magnitude. The total number of viruses in the global ocean estimated by bin-averaging and the random forest method was 1.56×10³⁰ and 1.49×10³⁰ particles, leading to an estimate of global ocean viral biomass at 35.9 and 34.4 Tg C, respectively. We expect that the gVOD will be a fundamental and very useful database for laboratory, field and modeling studies in marine ecology and biogeochemistry. The full gVOD database (Xie et al., 2020) is stored in PANGAEA (https://doi.org/10.1594/PANGAEA.915758).

Virioplankton is a key component of marine biosphere in maintaining diversity of microorganisms and stabilizing ecosystems. They also greatly contribute to nutrient recycles by releasing organic matter after lysis of hosts. In this study, we constructed the first global viral oceanography database (gVOD) by collecting 10 931 viral abundance (VA) data and 727 viral production (VP) data, along with host and other oceanographic parameters when available. Most VA data were obtained in the North Atlantic (32 %) and North Pacific Oceans (29 %), while the Southeast Pacific and Indian Oceans were quite under sampled. The VA in the global ocean was 1.17 (± 3.31) × 10⁷ particles ml⁻¹. The lytic and lysogenic VP in the global ocean was 9.87 (± 24.16) × 10⁵ and 2.53 (± 8.64) × 10⁵ particles ml⁻¹ h⁻¹, respectively. Average VA in coastal oceans was higher than that in surface open oceans [3.61 (± 6.30) × 10⁷ versus 0.73 (± 1.24) × 10⁷ particles ml⁻¹], while average VP in coastal and surface open oceans was close. Vertically, VA, lytic and lysogenic VP deceased from surface to deep ocean by about one order of magnitude. The total number of viruses in the global ocean estimated by bin average and random forest methods was 1.4 × 10³⁰ particles and 1.39 × 10³⁰ particles, leading to an estimate of global ocean viral biomass at 32.3 and 32.2 Tg C, respectively. We expect that the gVOD will be a fundamental and very useful database for laboratory, field and modeling studies in marine ecology and biogeochemistry. The full gVOD database is stored at PANGAEA (a temporary link: https://www.pangaea.de/tok/19f9d7b496a00f57f491e639440708aee00b6a49).