Bacteria with robust memories

Bacteria may not be the simple organisms we take them for. US biologists have found that bacterial cells stimulated with light remember the exposure hours after the initial stimulus.

The team from the University of California San Diego says it was even able to manipulate the process so that memory patterns emerged.

The findings reveal surprising parallels between low-level single-cell organisms and sophisticated neurons that process memory in the human brain, the researchers say, and provide a starting point for scientists to one day design basic computing systems with living organisms such as bacteria.

The research, which was led by Chih-Yu Yang, Maja Bialecka-Fornal, is described in a paper in the journal Cell Systems.

“Even just a few years ago people didn’t think bacterial cells and neurons were anything alike because they are such different cells. This finding in bacteria provides clues and a chance to understand some key features of the brain in a simpler system,” says co-author Gürol Süel. 

“If we understand how something as sophisticated as a neuron came to be – its ancient roots – we have a better chance of understanding how and why it works a certain way.”

Previous research by Süel and others has shown that bacteria use ion channels to communicate and suggested they might also have the ability to store information about their past states. 

In the new study, the researchers were able to encode complex memory patterns in bacterial biofilms with light-induced changes in the cell membrane potential of Bacillus subtilis bacteria. 

The optical imprints, they found, lasted for hours after the initial stimulus, leading to a direct, controllable single-cell resolution depiction of memory.

“When we perturbed these bacteria with light they remembered and responded differently from that point on,” says Süel. “So for the first time, we can directly visualise which cells have the memory. That’s something we can’t visualise in the human brain.”

The ability to encode memory in bacterial communities, the researchers say, could enable future biological computation through the imprinting of complex spatial memory patterns in biofilms.

“Being able to write memory into a bacterial system and do it in a complex way is one of the first requirements for being able to do computations using bacterial communities,” says Süel.

It may thus be possible, the researchers note in their paper, to imprint synthetic circuits in bacterial biofilms by activating different kinds of computations in separate areas of the biofilm.