Moore Foundation grantee Mick Follows and colleagues at the Massachusetts Institute of Technology have discovered bacteria and other tiny creatures in the ocean have a surprisingly low limit to the amount of oxygen they need to breathe.
Around the world, wide swaths of open ocean are nearly depleted of oxygen. Not quite dead zones, they are “oxygen minimum zones,” where a confluence of natural processes has led to extremely low concentrations of oxygen. Only the hardiest of organisms can survive in such severe conditions.
In a paper published recently in Limnology and Oceanography, Follows, an investigator through the foundation's Marine Microbiology initiative, reports that ocean bacteria can survive on oxygen concentrations as low as approximately one nanomolar per liter.
For context, this is approximately 10,000 times less oxygen than what small fish can tolerate and about 1,000 times less than what scientists previously thought marine bacteria could tolerate.
These researchers found below this critical limit, microbes either die off or switch to less common, anaerobic forms of respiration, taking up nitrogen instead of oxygen to breathe.
To study these marine bacteria, the team developed a simple model to simulate how a bacterial cell grows. Follows and his colleagues assumed that when oxygen is present, such microbes should use oxygen to breathe, as they would expend less energy to do so.
When oxygen concentrations dip below a certain level, bacteria should switch over to other forms of respiration, such as using nitrogen instead of oxygen to fuel their metabolic processes.
"We found that across all this parameter space, the critical limit was always centered at about 1 to 10 nanomolar per liter," said Emily Zakem, lead author of the research and a graduate student working in Follows' research group. "This is the minimum concentration for most of the realistic space you would see in the ocean. This is useful because we now think we have a good handle on how low oxygen gets in the ocean, and [we propose] that bacteria control that process."
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