SAR11 bacteria dominate the world’s…

SAR11 bacteria dominate the world’s oceans by being incredibly efficient, shedding genes to survive in nutrient-poor waters. But that extreme streamlining appears to backfire when conditions change. Under stress, many cells keep copying their DNA without dividing, creating abnormal cells that grow large and die. This vulnerability may explain why SAR11 populations drop during phytoplankton blooms and could become more important as oceans grow less stable.

To understand how SAR11 responds to environmental stress, researchers examined hundreds of SAR11 genomes. They found that many strains lack genes normally responsible for regulating the cell cycle, the system that controls DNA replication and cell division. In most bacteria, these genes are essential for normal growth and survival.

When environmental conditions shift, the absence of this regulation appears to create major problems. Scientists had already noticed that SAR11 populations are sensitive to changes in their surroundings. What stood out in this study was the unusual way the cells reacted under stress.