Some species of marine¹ phytoplankton（浮游植物）, such as the prolific² bloomer Emiliania huxleyi, can grow without consuming vitamin B1 (thiamine), researchers have discovered. The finding contradicts the common view that E. huxleyi and many other eukaryotic（真核的） microbes depend on scarce supplies of thiamine（硫胺素） in the ocean to survive. "It's a really different way to think about the ocean," says CIFAR Senior Fellow Alexandra Worden, co-author on The ISME Journal paper with CIFAR fellows John Archibald (Dalhousie University), Adrián Reyes-Prieto (University of New Brunswick) and three lead authors from Worden's lab at the Monterey Bay Aquarium³ Research Institute, Darcy McRose, Jian Guo and Adam Monier.

 

All living creatures need thiamine to live, as well as other vitamins. Organisms may produce some of their own vitamins, the way that human cells create vitamin D with help from sunlight, but sometimes they rely on other organisms to produce the vitamins they need and then consume them. For example, oranges and other fruits produce vitamin C, which humans need in their diets.

 

Until now, many marine microbes with cells that have a nucleus⁴ -- eukaryotes -- were thought to depend on other organisms to produce thiamine. If this were the case, B1 would be a major factor in controlling the growth of algae⁵ such as E. huxleyi, whose blooms are sometimes so large you can detect them from space. But the researchers found that E. huxleyi grows equally well in water that contains a precursor⁶ chemical to thiamine, known as HMP, as it does in an environment rich with thiamine. In fact, it could grow without any thiamine at all.

 

"If we added thiamine or we added the intermediate, there was absolutely no difference in the growth rate. They were growing equally well," Worden says.

 

It was the discovery of a surprising biological mechanism⁷ that led the researchers toward this new understanding of thiamine. Genetic⁸ analysis had revealed 31 new eukaryotic riboswitches, which are segments of RNA that operate like mechanical switches to turn genes⁹ on or off. The researchers then found, unexpectedly, that the riboswitches were tied to genes of unknown function, not genes known to be connected with the production of thiamine. Further testing revealed these organisms didn't only have a taste for thiamine -- they liked HMP too.

 

"Our study shows that conclusions regarding the importance of vitamin B1 in regulating algal communities need to be re-evaluated," Worden says.

 

This is the second recent study to find that vitamin B1 is less important than previously¹⁰ thought. Another paper in The ISME Journal published this August by Stephen Giovannoni's lab at Oregon State University found that the most abundant strain of bacteria in the ocean, SAR11, grows well in an environment with HMP but not with thiamine alone.

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