Viruses are the most prevalent biological entities in the world’s oceans and play essential roles in its ecological and biogeochemical balance. Yet, they’re the least understood elements of marine life.
By unraveling the entire genome of a certain marine organism — referred to by scientists as a “protist” — that may act as a host for many viruses, an international team led by researchers from Stony Brook University sets the stage for future investigations of marine protist genomes, marine microbial dynamics and the evolutionary interplay between host organisms and their viruses.
This work may open doors to a better understanding of the “invisible” world of marine viruses and offers a key to the ecology and health of oceans worldwide.
The research was published in the journal Current Biology.
In their paper, scientists built on previous discoveries of novel groups of viruses called “mirusviruses,” large DNA viruses sharing genes with both major realms of viral diversity. They’re believed to be ubiquitous in sunlit oceans, important to biodiversity and not likely harmful to human or aquatic life.
The discovery helps scientists better understand the biodiversity of plankton at the surface of the ocean, the importance of these viruses in the ecosystem and informs on the history of viruses.
The researchers made discoveries about the genome structure of the marine protist Aurantiochytrium limacinum. These findings not only shed light on the unique features of its chromosomes but also uncover the elusive hosts for mirusviruses.
Using advanced sequencing technologies, the team was able to completely assemble the genome of Aurantiochytrium.
They discovered two genomic elements with a strong resemblance to mirusviruses: One element is a circular structure present in high copies, while the other integrates within the end of a chromosome. These two states are reminiscent of herpesviruses, infamous for their ability to maintain latent infections in human and other animal hosts: some herpesviruses associated with cancer maintain latent infections by integrating into their host’s genome and others (like chickenpox) maintain latent infections as independent episomes.
The team discovered that Aurantiochytrium’s genome possesses a unique configuration at chromosome ends – an unexpected organization of genes and long repeats. The remarkable layout of these sequences may have a pivotal role in chromosome end maintenance, and it’s into one such region that a mirusvirus-like genome is integrated.
Jackie Collier, an associate professor at Stony Brook University and one of the authors of the study, said:
“Because mirusviruses were found using environmental sequence data, they were identified without known hosts. Our data show that A. limacinum is probably a natural host of mirusviruses and that a single host has been infected by multiple distinct viruses.”
By completing the entire genome of the protist, the researchers identified the first known host for mirusviruses, and their observations suggest dynamic host-virus genome interactions.
Collier’s colleague Joshua Rest, also from Stony Brook, said:
“The discovery of one of the viral sequences at one of the chromosome ends offers intriguing insights into the evolutionary ancestry of these elements. This revelation also aligns with growing evidence pointing toward mirusviruses’ significant influence in marine ecosystems.”
