Bacteria were swimming from the start

Being able to swim is important for many organisms for obvious reasons.

If I’m over here, something I want is over there, and between us is liquid, swimming is really the only game in town.

It’s also useful for evading predators.

Movement is life — just ask bacteria, they’ve been swimming for years, around 4 billion of them confirms a new study by a team of UNSW researchers published this month in The ISME Journal.

Bacteria have a remarkable set of tools to help them get around, most notably what’s called a “flagellar motor” — a protein structure so complex and elegant it was at one time falsely hailed as proof of intelligent design.

I GET AROUND

The Bacterial Flagellar Motor (BFM) is a marvel of nano-engineering and has transfixed microbiologists since it was first discovered in the 1970s.

Think of a rotary engine — it’s got a series of rings fixed to the cell wall which rotate a stand of protein known as a filament, driving the bacteria forward. 

It’s made of various proteins and it’s tiny — the rotor itself is only about 50 nanometres wide.

For reference, a strand of your hair is probably about 100,000 nanometres wide.

The confirmation that the Last Common Bacterial Ancestor (LCBA) could swim (or “was motile” as the scientists say) means that the ancestor of all bacteria alive today had some kind of motor that enabled it to move around.  

The LCBA lived around 4 billion years ago.

The team confirmed this early motility by analysing the genomes of more than 11,000 bacteria and figuring out what linked all the bacteria that could swim.

The team compiled a set of 54 proteins involved in flagellar motors and found that if one particular protein (FliC) is present, there’s a more than 90% chance that the bacteria will be motile.

All of this is possible using a set of computer programmes and databases that didn’t really exist a few years ago.

Once a laborious, expensive, and time-consuming task, scientists can now predict the structure of proteins accurately and quickly, giving scientists insights that just weren’t available until quite recently.

“Structural prediction has changed the field,” says study co-author Associate Professor Matthew Baker from the UNSW School of Biotechnology and Biomolecular Sciences of says.

“One of its biggest things it’s done is democratise structural biology,” 

“Someone like me, who didn't necessarily do much structural biology, or who doesn't have expertise in those experimental techniques, can whack in a sequence and get a structure.”

The study underscores the predictive power of genomics, meaning that going forward, scientists can estimate whether a bacteria is motile.

That’s because if FliC is present, it probably is.

BACTERIAL MOTILITY AND ME

Bacteria are everywhere for good or for ill (or most often, for neutral), so figuring out how they get around is pretty important.

When a scientist is looking at a disease, the first thing they’ll want to know pathogenic it is (i.e. how much damage it could do to your health).

Knowing whether its motile, and what mechanism it uses to get around, are key questions for scientists.

“We like to know whether things are motile or not,” A/Prof. Baker says.

“Being able to swim is increases your ability to infect things because you can move around.”

Two good examples of flagellar bacteria are E. coli and Salmonella, which rotate their motors hundreds of times a second enabling them to move around quickly and efficiently.

And understanding motility allows scientists to develop specific anti-motility compounds that render the bacteria immobile and thus less dangerous.

Maybe. 

As ever with cutting edge science, more work needs to be done.

WHAT USE IS HALF A MOTOR?

The thing is, a BFM is a sizeable energy investment for bacteria so motility must be highly beneficial otherwise evolution wouldn’t have bothered.

But that’s led scientists and philosophers wondering “what good is half a motor?”.

The thinking goes that the BFM didn’t evolve all at once, it likely took many generations for all the necessary proteins to line up one by one, enabling movement.

And before there’s movement, there’s a period where there are just a bunch of proteins inside the bacteria not doing much aside from costing energy to build and maintain.

"Creationists falsely claim this is evidence of Intelligent Design because if each subpart of a motor had no separate use, how could it all have just come together fully assembled without some ‘designer’”, A/Prof. Baker says.

This work further challenges this, because in their map of the BFM across the bacterial family tree they found there are in fact quite a lot of half motors throughout it. 

And A/Prof. Baker says that finding so many further indicates separate roles for these parts and can also occur when bacteria lose parts of a previously evolved motor, not gain them.

In fact, the authors found that bacteria lose genes related to flagellar motors four times more frequently than they gain them, raising some interesting questions about evolution.

That could suggest that these organisms are evolving to get less complex rather than more, flipping on its head the commonly held belief that evolution tends towards more complexity.

The study notes that certain proteins that enable motility also have other functions, which is why they’re not always lost when motility is.

But it could also be that the main energy gain comes from losing the filament (FliC), meaning the rest can stay, or even that the bacteria has evolved a different way to move around, leaving parts of the previous machine in-tact.

We don’t know yet, and A/Prof. Baker says more data is key.

“If we had more data points on these molecular complexes to compare to ancient molecular complexes that go way back to the Last Ancestor, we could potentially see how these different systems emerged and then evolved,” he says.