Some friendly bacteria wipe out their algal pals. Now we know why

Photosynthesizing plankton Emiliania Huxley It has a relationship with bacterial frenemies. These double help bugs E. huxleyi in the exchange of nutrients, until the army escapes their murders more conveniently. Now, scientists have figured out how these treacherous bacteria decide to turn from friend to foe.

One species of these bacteria seems to be keeping tabs on health-related products E. huxleyiinvestigators report on January 24 eLife. The bacteria maintain their friendly front until their hosts age and weaken as soon as the vulnerable algae can’t digest the nutrients. The discovery may help explain how the giant algal bloom ends.

The bacteria is “the first to establish what we call the ‘first handshake,'” says marine microbiologist Assaf Vardi of the Weizmann Institute of Science in Rehovot, Israel. “Then it will turn into a pathogen.”

E. huxleyiThe association with these bacteria, which belongs to a group called Roseobacter, best describes a love-hate relationship. A single-celled alga cannot produce B vitamins, which it needs by itself, so it provides nutrients that it can induce in Roseobacter.SN: 7/8/16). Trade wins – at least until the bacteria decide they’d be better off killing and devouring the algal hosts than hanging around in peaceful coexistence.

Sometimes called the “Jekyll-and-Hyde” trait, this bacterial species shows up as a backstabber everywhere from animal guts to the open seas. However, it is not clear how Roseobacter will decide the right time to kill E. huxleyi.

Vardi’s team exposed the type of Roseobacter when it lives E. huxleyi to chemicals derived from algae that were either young and aging or old and stagnant. The team also exposed the bacteria to extra doses of an algal chemical signaling health. Looking at which genes the bacteria produced in various experiments showed how and why they switched from friend to foe.

The bacteria kill their algae when exposed to high concentrations of a sulfur-containing chemical called DMSP, the researchers found. E. huxleyi pine more and more DMSP as it ages. Here he finally coaxes his double microbial partners to go rogue, kill the aging host, and kick in their genes for nourishing proteins and drive off the flagella—the tails of the flagella for swimming.

It’s an “eat and run strategy,” says Noa Barak-Gavish, a microbiologist at ETH Zurich. “You eat whatever you can and then swim to avoid the competition… [and] as a way of hosts.

DMSP is not the only figure on the lethal chemical scale. E. huxleyi he can saturate his blood with a bounty of benzoate, a nutrient that Roseobacter can use, but most bacteria cannot.

While it is now clearer what drives the bacteria to kill their hordes, their murderous weapon remains a mystery. Vardi tells his group to follow some humps in.

This type of frenetic relationship could be key in controlling the reef and the image of a giant algal bloom if other phytoplankton and bacteria have a similar dynamic, says Mary Ann Moran of the University of Georgia in Athens, who was not involved in the studies. Algal blooms are toxic (SN: 8/28/18). But they also emit “huge” amounts of carbon dioxide as biomass and are a major source of organic carbon to the ocean.

“Phytoplankton fix half of all the carbon on the planet, and probably 20 percent to 50 percent of what they … fix actually goes straight to the bacteria,” he said. So if this relationship controls how carbon flows through the ocean, “this is something we really need to understand.”