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. ...read more read less