Ecological characterization of viral communities in climate-sensitive environments using 'omics approaches

All of Earth’s ecosystems are affected by climate change, and many Northern ecosystems are particularly vulnerable to ecosystem disturbance. Viruses play key roles in ecosystem dynamics; viral infection can regulate microbial abundances and shape community composition, influence microbial evolution and metabolism, dictate the flux of carbon and nutrients, and more. Despite their recognized roles, our understanding of viral responses to global change is severely limited. Metagenomic approaches have expanded our knowledge of the diversity, distribution, and metabolic potential of uncultured viruses and are useful tools for interrogating viral assemblages across diverse environments. This dissertation uses metagenomic and metatranscriptomic approaches to characterize viral communities within the context of two Northern ecosystems sensitive to climate change. Chapter Two concerns the under-ice microbiome in Lake Erie, a seasonally frozen freshwater lake experiencing climate-driven declines in ice cover. Chapters Three and Four examine the microbiome of Sphagnum mosses, a keystone plant species in one of Earth’s largest terrestrial carbon sinks. Chapter Two presents a metatranscriptomic study comparing viral activity between an ice-covered and ice-free winter in Lake Erie, where we identified significant differences in active viral community composition and diversity. Chapter Three examined paired metagenomes and metatranscriptomes to define viral members of the core Sphagnum microbiome, providing evidence for persistent viral entities in association with Sphagnum communities. Chapter Four leveraged metagenomes and metatranscriptomes from warmed and ambient conditions to explore the effect of warming on viral community composition and activity in the moss microbiome. Here we found that viral communities were significantly different between warming conditions, but that differences may be dependent upon the type of warming condition and severity (artificial or natural geothermal warming). The chapters presented below span two different environmental systems, but they are linked by the interest in understanding microbial communities in Northern ecosystems disturbed by rapidly changing climate.