The word “virus” typically conjures associations with malady and apprehension regarding widespread contagions. However, within the marine environment, not all viral entities present adverse implications.
Certain viruses fulfill a beneficial, even indispensable, function in the perpetuation of oceanic lifeforms.
In a recent investigation, a collective of international scientific minds, including myself, meticulously analyzed the dynamics of marine viruses residing within a substantial stratum of oxygen-rich water situated just beneath the Atlantic Ocean’s surface. The revelations from this inquiry, particularly concerning their participation in the trophic web, illuminate marine viruses from a novel perspective.
Investigating Microscopic Entities
Viruses are characterized by their infinitesimal dimensions, generally not exceeding a few tens of nanometers in diameter. This makes them approximately a hundredfold smaller than bacteria and over a thousandfold smaller than the diameter of a human hair.
Indeed, their minute scale renders them imperceptible through conventional microscopy techniques.
(Sullivan, et al., 2005, PLOS One, CC BY)
In prior decades, the scientific consensus suggested that marine viruses were neither prolific nor ecologically consequential, notwithstanding their pronounced relevance to human, plant, and animal health.
Subsequently, advancements in transmission electron microscopy during the late 1980s precipitated a paradigm shift. Researchers gained the capability to scrutinize seawater samples at exceptionally high magnifications, revealing minute, spherical structures containing DNA. These were identified as viruses, and their abundance was found to be in the tens of millions per milliliter of water – a quantity orders of magnitude greater than previous estimations.
A Hypothesis on Viral Contributions to Marine Sustenance
The majority of marine viruses target the cellular components of microorganisms, specifically bacteria and algae, which form the fundamental basis of the ocean’s food web and are responsible for approximately half of the planet’s oxygen production.
By the close of the 1990s, it became apparent to scientists that viral activity profoundly influenced the cyclical transfer of carbon and nutrients within marine ecosystems. We proposed, through a conceptual framework termed the viral shunt model, that marine viruses lyse microorganism cells, thereby liberating their contained carbon and nutrients into the surrounding water column.
This mechanism has the potential to augment the nutrient availability for marine phytoplankton. Phytoplankton serve as a primary food source for zooplankton and fish, which, in turn, sustain larger marine organisms throughout the oceans. Consequently, viruses play a pivotal role in a food web that underpins a substantial global fisheries and aquaculture industry, yielding close to 200 million metric tons of seafood annually.
Observing Viral Activity in Situ
The recent investigation, published in the journal Nature Communications and spearheaded by the lead biologists Naomi Gilbert and Daniel Muratore, provided empirical validation of the viral shunt mechanism in operational terms.
The research team collected specimens from a stratified layer, spanning several meters in thickness and extending over hundreds of miles across the subtropical Atlantic Ocean. Within this specific oceanic zone, part of the Sargasso Sea, unicellular cyanobacteria known as Prochlorococcus are the dominant contributors to marine photosynthesis, with cell densities ranging from approximately 50,000 to over 100,000 per milliliter of seawater. These Prochlorococcus are susceptible to viral infection.
Through the sophisticated technique of community RNA sequencing—analyzing the messenger molecules that convey genetic information within cells—our team gained insight into the concurrent activities of virtually all viruses and their host organisms.
Our findings indicated that the incidence of viral infections within this oxygen-rich oceanic band is approximately four times elevated compared to other adjacent oceanic regions where cyanobacteria exhibit slower proliferation rates. Furthermore, we witnessed viral agents instigating extensive infections among Prochlorococcus populations.
The viruses effectively compromised host cells, leading to the release of organic matter. This liberated material was then assimilated by bacteria, serving as a substrate for their subsequent growth. The bacterial metabolic processes resulted in the consumption of carbon and the liberation of nitrogen in the form of ammonium.
This released nitrogen subsequently appeared to foster enhanced photosynthesis and the proliferation of additional Prochlorococcus cells, culminating in augmented productivity that generated the observed oxygen-rich stratum.
The viral infection exerted a demonstrable influence at the ecosystem level.
Appreciating the Significance of the Microscopic Realm
While viruses are known to trigger acute, chronic, and devastating health outcomes in humans and animals, this contemporary research, facilitated by a National Science Foundation-supported oceanographic expedition, contributes to an expanding body of evidence illustrating that viruses are fundamental agents in the operational mechanics of ecosystems, including their role in sequestering carbon within the deep ocean reservoirs.
We inhabit a planet undergoing continuous environmental transformation. The accurate monitoring and effective response to ecological shifts necessitate a comprehensive understanding of the microbial entities and underlying processes that govern global-scale phenomena.
This recent study underscores the critical importance of further exploration into the microscopic domain, encompassing the life cycles of viruses that exert considerable influence over microbial fates and the intricate workings of the Earth system.
