A bacterium has evolved into a new cellular structure inside algae

[BootinUp]

In the 3.5 billion years since life first evolved on Earth, it was thought that once-free-living bacteria had merged with other organisms on just three occasions, making this an exceedingly rare evolutionary event. Now, a fourth example has been found, in a single-celled alga common in the oceans.

These algae were thought to “fix” nitrogen – convert atmospheric nitrogen into useable ammonia – with the help of a bacterium. Tyler Coale at the University of California, Santa Cruz, and his colleagues have now shown that this bacterium has evolved into a new cellular structure, or organelle.

It is the first known nitrogen-fixing organelle, or nitroplast, says Coale, and could be the key to the success of these algae. “It appears to be a successful strategy for them,” he says. “These are very widespread algae. We find them all over the world’s oceans.”

It is quite common for one species to live inside the cells of another in a mutually beneficial relationship called endosymbiosis. For instance, cells in the roots of legumes such as peas host nitrogen-fixing bacteria. The success of cockroaches is partly due to endosymbiotic bacteria that produce essential nutrients. Some cells even host multiple endosymbionts.

continued at NewScientist.com

https://www.newscientist.com/article/2426468-a-bacterium-has-evolved-into-a-new-cellular-structure-inside-algae/