Understanding the roles of viruses as key players in environmental dynamics and ecosystem functioning

Viruses are ubiquitous and have successfully established themselves in all natural and artificial habitats, contributing to the ecosystems with the highest number of representatives. The interaction of viruses with their cohabitants and inanimate ecological entities has now been recognized as crucial regulators of environmental dynamics and biodiversity. The discovery of new culture-independent and in silico techniques to study viruses (i.e. viromics) has enabled scientists to study the viral diversity of any habitat in more detail and to understand the impact of viruses on the environment. Towards this, hundreds of samples collected from marine, freshwater, and terrestrial ecosystems have been studied to explore viral diversity, and how viruses control microbial community composition thereby playing crucial roles in regulating primary productivity and biogeochemical processes in an ecosystem through altering carbon and nutrient flows. Phage virus-mediated regulation of human microflora and gene transfer in the intestinal microbiota have been proven significant in the health and disease outcomes of individuals. Viruses can also manipulate the metabolic processes of their interacting species by encoding auxiliary metabolic genes (AMGs), and their unique life cycles facilitate complex interactions across diverse ecosystems influencing nutrient cycling, population control, and genetic exchange. Here, we have reviewed and discussed the viral diversity of the major ecosystems, their role in biogeochemical cycles, the importance of the AMGs, the ecological significance of virus-mediated lateral gene transfer, and the ecological roles of virus-virus interactions. Currently, the investigation of the ecological importance of viruses has gradually become a mainstream research area in environmental sciences.