The ocean's most abundant bacteria, SAR11, may be more vulnerable to environmental change than previously thought. These bacteria, which dominate surface seawater worldwide and make up to 40% of marine bacterial cells, have evolved to thrive in nutrient-poor waters through genome streamlining. However, a recent study reveals a potential flaw in their adaptation strategy.
The research, published in Nature Microbiology, suggests that SAR11's extreme efficiency comes at a cost. Many of these bacteria lack the genes required to control the cell cycle, a process crucial for healthy growth in most bacteria. When exposed to changing environmental conditions, this lack of regulation leads to serious cellular issues.
What's surprising is how SAR11 cells respond to stress. Instead of slowing growth, many cells continue to copy their DNA while failing to divide, resulting in cells with abnormal chromosome numbers. These abnormal cells often become enlarged and eventually die, causing a slowdown in overall population growth, even when nutrients are abundant.
This finding challenges common assumptions about microbial growth and helps explain why SAR11 populations often decline during the later stages of phytoplankton blooms, when organic matter increases. The study also has broader implications for understanding climate change and marine ecosystems, as SAR11 bacteria play a significant role in ocean carbon cycling.
As environmental stability declines, organisms with greater regulatory flexibility may gain an advantage. Future research will focus on uncovering the molecular mechanisms behind these disruptions, which will enhance our understanding of SAR11's role in marine carbon cycling and its potential impact on ocean ecosystems.
