Marine bacteria play a crucial role in determining whether carbon is recycled near the ocean surface or transported to deeper waters. However, their function is constantly threatened by viral infections from phages, leading to a continuous evolutionary battle. This arms race raises significant questions about the costs of bacterial resistance to infections and the subsequent effects on ocean ecosystems.
A recent study published in Nature Microbiology delves into the mechanisms of phage resistance and its impact on the ecological roles of ocean bacteria. Researchers discovered that certain mutations not only fail to hinder but may actually enhance the bacteria’s ability to capture and sink carbon to the ocean floor by making the cells “stickier.”
Understanding Phage Resistance
The study identified two types of mutations in bacteria: surface mutations that prevent phage entry and metabolic mutations within the bacteria. The latter are less studied and suggest that while a virus may enter the cell, it cannot replicate effectively.
“We found that both metabolic and surface mutations caused the bacteria to get stickier, but only in surface mutants did those changes cause the cells to sink much more readily. That was very, very obvious,” said Marion Urvoy, co-first author of the study and a postdoctoral research associate in microbiology at The Ohio State University.
The research focused on 13 phage-resistant mutants derived from Cellulophaga baltica bacteria, tested against two types of phages. The findings revealed that surface mutations provided broad resistance to multiple phages, while metabolic mutations offered specific resistance to individual phages.
Implications for the Marine Carbon Cycle
The study’s findings have significant implications for the marine biological pump, a process critical for carbon sequestration in the ocean. The enhanced stickiness and sinking ability of surface mutants could play a vital role in this process.
“Carbon export in the ocean is important. From past papers, we know that virus abundance is the best predictor of carbon export, more so than any other organism, but we don’t know all the mechanisms behind this,” Urvoy explained.
This research builds on earlier work by co-first author Cristina Howard-Varona, which showed that cyanobacteria might increase carbon intake when infected by phages and stressed by nearby predators. Howard-Varona plans to further investigate the mechanisms behind metabolic mutations against phages.
“This really opens the gate to wanting to examine more intracellular resistance because it’s so understudied,” Howard-Varona said. “If we add more types of phages, do you get more mutations and more types of mechanisms that we don’t know about? This is really just the tip of the iceberg.”
Broader Ecological and Climate Implications
The study was conducted under the guidance of Matthew Sullivan, a professor at Ohio State, whose research focuses on the impact of viruses on microbiomes across various environments. Understanding the role of viruses in carbon cycling is crucial, as it affects global climate change.
“It’s important to understand what happens in the ocean because it affects climate globally. For microorganisms, we need to understand their impacts on carbon because they dictate whether carbon sinks or gets released into the atmosphere, and that outcome impacts our lives,” said Urvoy.
This research was supported by the U.S. National Science Foundation, the U.S. Department of Energy, and the Swedish Research Council, with contributions from multiple institutions, including Oak Ridge National Laboratory and Linnaeus University in Sweden.
As scientists continue to explore the complex interactions between marine bacteria and phages, the findings could lead to a deeper understanding of the ocean’s role in regulating Earth’s climate and the potential for mitigating climate change.
