How Giant Viruses Manipulate Ocean Plants to Shape Marine Food Webs

Giant viruses, once a mystery, are now thought to play a crucial role in ocean ecosystems. They infect protists, which are tiny, single-celled organisms like algae and amoebas. These protists form the base of the marine food web. When giant viruses invade these organisms, it can disrupt the entire ecosystem, sometimes causing harmful algal blooms that threaten marine life and even human health.

Researchers are eager to unlock the secrets of these giant viruses. Understanding them better could help predict when and where these dangerous blooms will occur. This knowledge is vital for protecting coastal communities. A team from the Rosenstiel School of Marine has made significant progress by analyzing a vast collection of environmental DNA sequences from oceans around the world.

By using advanced tools, they discovered 230 new giant virus genomes from diverse ocean regions, including the Arctic Ocean and the South Pacific. Interestingly, the Baltic Sea was a hotspot, yielding the most findings—108 high-quality viral genomes.

In their research, the team also identified 398 partial genomes, greatly increasing the known diversity of giant viruses. Most of these belong to two major groups: Imitervirales and Algavirales. Notably, they also found rare members of the Mirusviricota order, shedding light on the evolutionary links between giant viruses and herpesviruses.

The new genomes often contain large structures—some exceeding 1.3 million base pairs. Certain groups showed unique traits, like high GC content affecting DNA behavior. The researchers didn’t stop at just sequencing. They also looked at the proteins within these viruses, examining the nitrogen and sulfur content in each protein chain. High nitrogen levels can indicate how these viruses affect host resources during infection.

This research revealed that these giant viruses possess genes related to photosynthesis and carbon metabolism—functions typically found in cellular organisms. For example, the Imitervirales lineage displayed many of these genes, suggesting a strategy that manipulates host metabolism more than the Algavirales, which had fewer even though their genomes were larger.

The unique conditions in the Baltic Sea, such as its salinity and depth, influenced the viral diversity there. This study helps create a framework for better detection of new viruses, which is crucial for monitoring pollution and pathogens in our waterways.

One surprising aspect is how these giant viruses can alter the photosynthetic processes in their hosts. By manipulating systems like photosystems I and II, they can sustain energy production during infection. This is crucial since giant viruses are often responsible for the death of phytoplankton, the foundation of oceanic food webs.

The team’s findings were enabled by a new tool named BEREN, which identifies giant viruses in public DNA databases. Rather than reanalyzing existing data, they focused on untouched samples, leading to their groundbreaking discoveries.

Despite recovering only about 1,800 marine virus genomes to date, the potential for finding more is vast. This shows how giant viruses may have a significant impact on entire ecosystems.

The study was published in the journal npj Viruses, making the data and findings accessible for further exploration and research.

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