Viruses modulate the function(s) of environmentally relevant microbial populations, yet considerations of the metabolic capabilities of individual virus particles themselves are rare. We used shotgun proteomics to quantitatively identify 43 virus-encoded proteins packaged within purified Aureococcus anophagefferens Virus (AaV) particles, normalizing data to the per-virion level using a 9.5-Å-resolution molecular reconstruction of the 1900-Å (AaV) particle that we generated with cryogenic electron microscopy. This packaged proteome was used to determine similarities and differences between members of different giant virus families. We noted that proteins involved in sugar degradation and binding (e.g., carbohydrate lyases) were unique to AaV among characterized giant viruses. To determine the extent to which this virally encoded metabolic capability was ecologically relevant, we examined the TARA Oceans dataset and identified genes and transcripts of viral origin. Our analyses demonstrated that putative giant virus carbohydrate lyases represented up to 17% of the marine pool for this function. In total, our observations suggest that the AaV particle has potential prepackaged metabolic capabilities and that these may be found in other giant viruses that are widespread and abundant in global oceans.

Microcystins produced during harmful cyanobacterial blooms are a public health concern. Although patterns are emerging, the environmental cues that stimulate production of microcystin remain confusing, hindering our ability to predict fluctuations in bloom toxicity. In earlier work, growth at cool temperatures relative to optimum (18°C vs. 26°C) was confirmed to increase microcystin quota in batch cultures of Microcystis aeruginosa NIES-843. Here, we tested this response in M. aeruginosa PCC 7806 using continuous cultures to examine temporal dynamics and using RNA-sequencing to investigate the physiological nature of the response. A temperature reduction from 26 to 19°C increased microcystin quota ∼2-fold, from an average of ∼464 ag μm–3 cell volume to ∼891 ag μm–3 over a 7–9 d period. Reverting the temperature to 26°C returned the cellular microcystin quota to ∼489 ag μm–3. Long periods (31–42 d) at 19°C did not increase or decrease microcystin quota beyond that observed at 7–9 d. Nitrogen concentration had little effect on the overall response. RNA sequencing indicated that the decrease in temperature to 19°C induced a classic cold-stress response in M. aeruginosa PCC 7806, but this operated on a different timescale than the increased microcystin production. Microcystin quota showed a strong 48- to 72-h time-lag correlation to mcy gene expression, but no correlation to concurrent mcy expression. This work confirms an effect of temperature on microcystin quota and extends our understanding of the physiological nature of the response.

abundances were related in a predictable way it would be possible to infer the rate of contact, and potentially the relative importance of virus-induced cell lysis, from estimates of microbial abundance alone.Virus ecology underwent a transformation in the late 1980s with the recognition that virus abundances, as estimated using culture-independent methods, were orders of magnitude higher than estimates via culture-based methods [4]. Soon thereafter, researchers began to report the "virus to bacterium ratio" (VBR) as a statistical proxy for the strength of the relationship between viruses and their potential hosts in both freshwater and marine systems [31]. This ratio is more appropriately termed the "virus-to-prokaryote ratio" (VPR) -a convention which Typeset by REVT E X

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Over the last two decades, viruses in aquatic systems have been observed to modify, influence and control aquatic systems. Since the determination decades ago that viruses were abundant in aquatic ecosystems, researchers have demonstrated that viruses are pervasive and dynamic across the expanse and depth of all aquatic systems as well as at the water-sediment interface. There have been a wide range of methodological advancements during this time. To date, aquatic viruses have been suggested to play vital roles in global and small-scale biogeochemical cycling, community structure, algal bloom termination, gene transfer, and evolution of aquatic organisms. Even in harsh and difficult to study environments, aquatic and benthic viruses have been demonstrated to be major players in carbon cycling and recycling of nutrients from organic material. Taxonomic and metagenomic research has shown us that there are major globally-distributed groups, but that their genomes are filled with sequence information that has no similarity to sequences in existing bioinformatic databases. And while the field of viral ecology has expanded exponentially since the late 1980s, there is much that we do not yet understand about virusmediated processes in aquatic systems. Important near-term steps include the combination of advanced metagenomic techniques with studies of function and population control, standardization of methodological approaches to facilitate global data acquisition without concern over methods-based artefacts, understanding of viral life strategies and their triggers, and the role of viruses in the transformation of organic matter. The purpose of this manuscript is to bring the reader a review of the recent advances in aquatic viral ecology in light of new areas of research, applications of viral ecology to real-world problems, and refinement of models of viral interactions on a range of scales.