RESUMO
Genomic studies on sequence composition employ various approaches, such as calculating the proportion of guanine and cytosine within a given sequence (GC% content), which can shed light on various aspects of the organism's biology. In this context, GC% can provide insights into virus-host relationships and evolution. Here, we present a comprehensive gene-by-gene analysis of 61 representatives belonging to the phylum Nucleocytoviricota, which comprises viruses with the largest genomes known in the virosphere. Parameters were evaluated not only based on the average GC% of a given viral species compared to the entire phylum but also considering gene position and phylogenetic history. Our results reveal that while some families exhibit similar GC% among their representatives (e.g., Marseilleviridae), others such as Poxviridae, Phycodnaviridae, and Mimiviridae have members with discrepant GC% values, likely reflecting adaptation to specific biological cycles and hosts. Interestingly, certain genes located at terminal regions or within specific genomic clusters show GC% values distinct from the average, suggesting recent acquisition or unique evolutionary pressures. Horizontal gene transfer and the presence of potential paralogs were also assessed in genes with the most discrepant GC% values, indicating multiple evolutionary histories. Taken together, to the best of our knowledge, this study represents the first global and gene-by-gene analysis of GC% distribution and profiles within genomes of Nucleocytoviricota members, highlighting their diversity and identifying potential new targets for future studies.
RESUMO
The global demand for industrial enzymes has been increasing in recent years, and the search for new sources of these biological products is intense, especially in microorganisms. Most known viruses have limited genetic machinery and, thus, have been overlooked by the enzyme industry for years. However, a peculiar group of viruses breaks this paradigm. Giant viruses of the phylum Nucleocytoviricota infect protists (i.e., algae and amoebae) and have complex genomes, reaching up to 2.7 Mb in length and encoding hundreds of genes. Different giant viruses have robust metabolic machinery, especially those in the Phycodnaviridae and Mimiviridae families. In this review, we present some peculiarities of giant viruses that infect protists and discuss why they should be seen as an outstanding source of new enzymes. We revisited the genomes of representatives of different groups of giant viruses and put together information about their enzymatic machinery, highlighting several genes to be explored in biotechnology involved in carbohydrate metabolism, DNA replication, and RNA processing, among others. Finally, we present additional evidence based on structural biology using chitinase as a model to reinforce the role of giant viruses as a source of novel enzymes for biotechnological application.