People love bringing up E. coli whenever this sort of thing comes up, but it's not a compelling argument. It generally refers to the observation that if you have a bacterium swimming towards something that's bad (ie, an increasing concentration of a toxic molecule), it'll tend to start swimming away. The obvious implication is that the bacterium has to remember that it's trying to swim away from something in order to keep doing so.
In reality, we've had an alternative explanation for about 20 years. The chemical receptors that respond to the molecules E. coli wants to get away from activate and generate a cascade that causes the flagella (the stranded "tail" molecules that allow them to swim) to start rotating in the opposite direction. This causes them to become tangled, and this results in the bacterium moving around randomly rather than making any progress in one direction. If it heads away from the noxious source, the receptors stop activating, the flagella start rotating in the correct direction, and it heads off in a straight line again.
But what about the memory? If the bacterium didn't remember what happened, isn't there a high chance that it would just end up doing the same thing again? Yes, but we don't need to bring RNA into this. One of the molecules involved in the cascade is activated by phosphorylation - once phosphorylated, its sensitivity changes. Over time, another molecule dephosphorylates it, but this altered sensitivity means the bacterium is more sensitive to the noxious molecule than it was previously and biases the bacterium to move away.
So "memory" in this case is actually just a modification of the gain in the response to a stimulus. Does it demonstrate that responses can be influenced by something that happened in the past without requiring a nervous system? Yup, absolutely. Is it something that gives us a better understanding of how rich long term memories are stored in the brain? Not really.
(Source: my first attempt at a PhD was working with https://en.wikipedia.org/wiki/Dennis_Bray who did a bunch of the computational modelling that demonstrated we didn't need anything overly complicated to understand what was going on here. Absolutely wonderful scientist, but I fell out with departmental IT staff over network security stuff. Ironic with hindsight. Also, this is my recollection from almost 20 years ago, so details may be inaccurate)
In reality, we've had an alternative explanation for about 20 years. The chemical receptors that respond to the molecules E. coli wants to get away from activate and generate a cascade that causes the flagella (the stranded "tail" molecules that allow them to swim) to start rotating in the opposite direction. This causes them to become tangled, and this results in the bacterium moving around randomly rather than making any progress in one direction. If it heads away from the noxious source, the receptors stop activating, the flagella start rotating in the correct direction, and it heads off in a straight line again.
But what about the memory? If the bacterium didn't remember what happened, isn't there a high chance that it would just end up doing the same thing again? Yes, but we don't need to bring RNA into this. One of the molecules involved in the cascade is activated by phosphorylation - once phosphorylated, its sensitivity changes. Over time, another molecule dephosphorylates it, but this altered sensitivity means the bacterium is more sensitive to the noxious molecule than it was previously and biases the bacterium to move away.
So "memory" in this case is actually just a modification of the gain in the response to a stimulus. Does it demonstrate that responses can be influenced by something that happened in the past without requiring a nervous system? Yup, absolutely. Is it something that gives us a better understanding of how rich long term memories are stored in the brain? Not really.
(Source: my first attempt at a PhD was working with https://en.wikipedia.org/wiki/Dennis_Bray who did a bunch of the computational modelling that demonstrated we didn't need anything overly complicated to understand what was going on here. Absolutely wonderful scientist, but I fell out with departmental IT staff over network security stuff. Ironic with hindsight. Also, this is my recollection from almost 20 years ago, so details may be inaccurate)