Beneath the Waves: Unraveling the Hidden Web of Oceanic Bacteria

Subsequently, to determine if the connections were indeed nanotubes, they conducted various iterations of the now-standard experiments utilizing green fluorescent protein and calcein outlined by Ben-Yehuda and Dubey. The interconnected cells illuminated. The researchers also validated that the connections were composed of membrane lipids rather than proteins, which would imply pili instead. They were ultimately convinced that they were observing bacterial nanotubes.

They came to realize that these tubes link some of the most prevalent organisms on Earth. This realization sparked a profound insight, one that the scientists are still contemplating.

“At the onset of this century, discussions regarding phytoplankton in the ocean focused on individual cells that operate independently,” García-Fernandez noted. “However, now — and not only based on these findings but also on results from others — I believe we must consider that these organisms do not function in isolation.”

A Cellular Web

There may be a compelling rationale for why cyanobacteria, adrift in the extensive ocean, would choose to collaborate. They possess notably small genomes, remarked Christian Kost, a microbial ecologist from the University of Osnabrück in Germany who was not part of this research. Prochlorococcus has the smallest genome of any recognized free-living photosynthetic cell, containing approximately 1,700 genes. Synechococcus is close behind.

In bacterial species, reduced genomes alleviate the burden of maintaining extensive DNA; however, this condition also necessitates that they acquire various essential nutrients and metabolites from neighboring organisms. Bacteria with streamlined genomes often establish interdependent communities with species that produce what they require and need what they generate.

“This arrangement can be significantly more efficient than a bacterium striving to generate all metabolites simultaneously,” Kost stated. “What poses a challenge, when residing in a liquid environment, is: How do you exchange these metabolites with other bacteria?”

Nanotubes could provide a solution. Nutrients relayed through this method will not be carried away by currents, lost to dilution, or consumed by opportunists. In computational simulations, Kost and his team discovered that nanotubes can foster the promotion of cooperation among bacterial groups.

Furthermore, “this [new] paper indicates that this transfer occurs both within and across species,” he observed. “This is exceptionally intriguing.” In a preceding study, he and his colleagues also detected various bacterial species interlinked by nanotubes.

This type of cooperation is likely more prevalent than many realize, asserted Conrad Mullineaux, a microbiologist at Queen Mary University of London — even in conditions such as the open ocean, where bacteria might not always be in proximity to establish nanotubes.

Often, we regard bacteria as straightforward and unicellular. Yet, bacterial colonies, biofilms, and consortia of diverse microorganisms are capable of executing intricate feats of engineering and behavior collectively, sometimes rivaling the accomplishments of multicellular organisms. “I occasionally attempt to convince people, particularly when I’m feeling spirited: You are a biofilm and I am a biofilm,” Mullineaux remarked. If the ocean is filled with cyanobacteria communicating via nanotubes and vesicles, then perhaps this resource exchange could influence fundamental aspects like atmospheric oxygen levels or the amount of carbon sequestered in the ocean.

Kost, Ben-Yehuda, and Mullineaux concur that the findings of the new paper are fascinating. The authors have performed all the necessary tests to confirm that the structures they are observing are indeed nanotubes, they asserted. However, further investigation is essential to comprehend the implications of this finding. In particular, an important open question is what, precisely, Prochlorococcus and Synechococcus are exchanging with each other in their natural habitat. While photosynthesis enables these bacteria to harness energy from the sun, they must procure nutrients such as nitrogen and phosphorus from their surroundings. The researchers are initiating a series of experiments with Rachel Ann Foster from Stockholm University, an expert in nutrient flow within the ocean, to trace these substances in networked cells.

Another query pertains to how bacteria develop these tubes and under which circumstances. The tubes are not significantly longer than an individual cell, and Prochlorococcus, specifically, is believed to disperse throughout the water column. Muñoz-Marín and her team are inquisitive about the bacterial concentrations needed for a network to form. “How frequently would it be feasible for these independent cells to come close enough to one another to develop these nanotubes?” García-Fernandez inquired. The current research indicates that nanotubes do form among naturally collected cells, yet the exact prerequisites remain unclear.

Reflecting on the perceptions regarding bacterial communication when he began investigating marine cyanobacteria 25 years ago, García-Fernandez is mindful of the significant transformations the field has experienced. Scientists once believed they observed countless individuals drifting alongside one another in immense distances, competing with neighboring species for resources. “The realization that physical communication can occur between different types of organisms — I believe that alters many, many prior concepts regarding the functioning of cells in the ocean,” he expressed. It is a far more interconnected ecosystem than anyone had comprehended.