Unique T4-like phages in high-altitude lakes above 4500 m on the Tibetan Plateau

Highlights: • VBR in Tibetan lakes was in the lower range of values reported for other lakes. • Highly diverse morphologies of virus-like particles were observed in Tibetan lakes. • A novel T4-like myovirus group unique to Tibetan Plateau lakes was identified. • Environmental conditions led to the variation of virus community in Tibetan lakes. Viruses are the most abundant biological entities in the biosphere; however, little is known about viral ecology in high altitude lakes. Here, we characterized viruses from 13 lakes, nine of which located ≥4500 m above sea level, on the Tibetan Plateau, the highest plateau on Earth. The abundance of virus-like particle (VLP) in Tibetan lakes ranged from 4.8 ± 0.2 × 10⁵ VLPs mL⁻¹ to 6.0 ± 0.2 × 10⁷ VLPs mL⁻¹ and the virus-to-bacterium ratio was in the lower range of values reported for other lakes. The viral population size was positively correlated with turbidity and negatively correlated with particulate organic carbon concentration. Highly diverse VLP morphologies, including large (~300 nm) morphotypes, were observed. Phylogenetic analysis of T4-like bacteriophages based on major capsid gene (g23) identified a novel viral group, which were detected in abundance in hyposaline and mesosaline Tibetan lakes. Adaptation to lake evolution, water source (glacier-fed or non-glacier-fed) and environmental conditions (e.g., salinity, phosphorus concentration and productivity) are likely responsible for the variation in T4-like myovirus community composition in contrasting Tibetan lakes. This first investigation of viruses in high-altitude alpine lakes above 4500 m could contribute to our understanding of viral ecology in global alpine lakes.