Do bacteria have brains?
Next time you’re tempted to feel sorry for yourself, you may choose to thank your lucky stars you weren’t born an Acanthonus armatus.
If you had been, you’d be an odd type of tadpole-looking deep-sea fish with two enormous reasons not to be cheerful.
First, you’d have the smallest brain to body weight of all known vertebrates.
There’s worse to come, though.
Your common name would be the Bony-Eared Assfish.
And you thought you had it bad.
I bring this unfortunate, pea-brained fish to your attention in part because I believe it is next to impossible to read “Bony-Eared Assfish” without at least a modest smile, which I’m sure we all need on a Monday, but also because I want to address that old question: “Do bacteria have brains?”
You see, although the short answer is “No,” the longer answer is “Well not exactly—but it’s very interesting…”
Technically, scientists define a brain as an organ composed of many cells, so a single-celled organism such as a bacterium obviously can’t have one of those.
But this doesn’t prevent bacteria doing things which seem on the face of it pretty darned clever.
For example, how is it that bacteria are able to move towards food, or away from pathogens which could hurt them?
Well, there are receptors on the surface of a bacterial cell which pick up signals from external chemicals.
And when the receptors on one side of the cell pick up more signals than those on the other, the microbe can “decide” to either move in that direction—if it’s food—or scurry off the other way if it’s something toxic.
Many bacteria travel using a kind of tail called a flagellum, which which acts a bit like a propeller, powered by a protein “motor”.
When there’s food on their table, or something nasty lurking, bacteria don’t exactly hang around.
One of the very speediest, for example, Bdellovibrio bacteriovorus, can move 100 cell lengths a second, the equivalent of a six-foot human running at 400 mph.
To some extent, therefore, even though bacteria don’t have brains, they can move intelligently.
But what about other functions that a brain might deliver?
Surely bacteria don’t have memories or communication abilities, for example?
Well, think again.
Consider the fact that many types of pathogenic bacteria are becoming increasingly resistant to antibiotics, a huge problem in the healthcare world.
Does this mean that bacteria are somehow learning?
In some ways, yes.
Once a bacterium has figured out a way to halt the attack of an antibiotic, it’s able to maintain the necessary genes for future use, and these are passed on as the cell reproduces.
Interestingly, however, this “memory effect” seems to depend on the microbes remaining within their host.
Austrian researchers in 2014 demonstrated this by taking Listeria monocytogenesfrom mice and discovering that the cells’ metabolic response was different once it was growing on a Petri dish in the lab.
Their “memory” seemed to fade once away from their host.
Other scientists, though, believe that bacteria can be persuaded to develop elephant-like memories.
In 2014, a team at MIT turned E. coli bacteria into a long-term storage device which they termed a “genomic tape recorder.”
They were able to insert DNA into a targeted site within the bacteria, making a “recording” which could then be replayed by sequencing the DNA in the same way we do at uBiome.
The scientists believe that considerable amounts of data could be stored in this way, meaning that re-engineered bacteria could, for example, be designed to live in the human digestive tract to monitor dietary intake.
Even more recently, UCSD researchers in 2015 conducted a study suggesting that bacteria might well be able to communicate from cell to cell.
They noticed that tartar on teeth caused by Bacillus subtilis grows to a certain thickness, then periodically stops before restarting its growth again.
This happens even when all the right nutrients are present.
What’s going on, they believe, is that bacteria in the sheltered center of this biofilm communicate their need for nutrients to their fellow tooth-riders on the surface so rather than being consumed up there, the bacteria-food gets passed down the chain into the center.
The researchers suggest that bacteria communicate using the same kind of electrical signalling mechanism as neurons in the human brain.
All in all, therefore, the fact that bacteria don’t have brains doesn’t stop them being pretty smart.
Even more reason to not only love your bacteria, but to respect them too.