Scientists have caught a once-in-a-billion-years evolutionary event in progress, as two lifeforms have merged into one organism that boasts abilities its peers would envy. Last time this happened (1.6 billion years ago), certain advanced cells absorbed a type of bacteria that could harvest energy from sunlight. These became organelles called chloroplasts, which gave sunlight-harvesting abilities, as well as a fetching green color, to a group of lifeforms you might have heard of – plants.
And now, scientists have discovered that it’s happening again. A species of algae called Braarudosphaera bigelowii was found to have engulfed a cyanobacterium that lets them do something that algae, and plants in general, can’t normally do – "fixing" nitrogen straight from the air, and combining it with other elements to create more useful compounds.
As any farmer or gardener will tell you, nitrogen is critical for plant growth, and for most plants it's obtained via the soil. Soil nitrogen can be depleted if not replenished (in an agricultural context, by compost or fertilizer), but there's plentiful nitrogen in the atmosphere (which is mostly nitrogen, actually) so any plant that has nitrogen fixing abilities has constant access to this critical nutrient. There currently exist nitrogen-fixing plants (peas and clover for example), but they don't actually do it on their own, they rely on a symbiotic relationship with bacteria.
Nitrogen is crucial for duplicating DNA, which needs to happen for vells to divide. Despite being over 70% of the atmosphere, nitrogen gas is incredibly inert, so most organisms cant use it for any metabolic purposes. There are many bacteria that are able to break down nitrogen gas into useable nitrates, most famously those that live in the root systems of legimes like soy and peanuts, which is why American corn farmers grow so much soy.
So the last time was chloroplasts, right? And that worked out super well for all the other organisms and didn't do anything catastrophic to the atmosphere, right?
You commit one murder and no one let's you live it down, meanwhile The Sisko renders a planet uninhabitable to humans and tricks a foreign government into joining your war and no one bats an eye.
This isn't that uncommon, it's just really hard for it to survive into reproduction. Protists are notorious for it, this one alone has at least three separate bacterial symbiotes and even replaced it's own mitochondria(which themselves are endosymbiotic bacteria) with another bacteria, essentially reinventing the fucking wheel: https://en.m.wikipedia.org/wiki/Mixotricha_paradoxa
As a layman, my interpretation is that scientists have observed a mutation in some prehistoric cells / creatures that is likely positive. In this case an algae and a bacteria somehow combined in such a way that they have become something new and better.
As an optimistic guesser it seems like this probably happens fairly often and is either unlikely to survive or replicate for long. But, having observed something that we have known about is further evidence that we understand ongoing evolution and may have a better, more sound understanding of how life came to be.
I guess that's probably interesting because it helps us better understand what the building blocks for life are, and as we discover them on other planets or in other places in outer space we may better be equipped to understand how or if life exists outside our own world.