Even single-celled organisms have a type of personality, in that they may respond to the same circumstances differently from others of their species. Indeed, even when compared to those with identical genetics, bacteria can reveal their individuality.
Bacteria use chemical gradients to identify the direction in which they should move, either towards food or away from something that may harm them. Dr Mehdi Salek and Dr Francesco Carrara of MIT created a microscopic version of the mazes used to test animal decision-making and placed an attractant at one end.
In theory, bacteria should have been able to detect the gradient in the maze and choose the forks in the road that led them to a bacterial feast. In Nature Communications, the authors report most E. coli did just that. Others, however, took an apparently wrong turning, not just once but repeatedly, being either less able to track their surroundings or to use their flagella (structures that essentially act as propellers) to turn. Remarkably these were not different strains, let alone different species, of bacteria, but clones with identical genetics.
From an evolutionary point of view, this is a very wise strategy. If bacteria ignored the cues in their environment they'd do very badly. However, if all converged on a single source of food they would be vulnerable to threats and might miss other, possibly richer, sources that may be more distant or masked for some reason. Having a few take the road less traveled by raises the chance some will capture the available resources. Given the speed with which a lonesome cell can multiply, it only takes one to find the hidden store and an abundance will follow, ensuring the continuation of the genes.
However, simplistic descriptions of biology that represent DNA as destiny can't explain the process. Naturally, Salek and Carrara have a much deeper understanding. "There is biochemical noise in every cell. As a fundamental random component, this causes diversity of appearance and behavior," they note.
"Non-genetic diversity has long been known in the biomedical life sciences; for example, it is thought to play a role in antibiotic resistance,” said senior author Dr Roman Stocker in a statement. “Now, environmental scientists have shown that this diversity also affects fundamental behaviors of bacteria... further expanding the concept of bacterial individuality.”
The findings could be important for the ways we interact with bacteria, for example controlling pathogens. They also have implications for how we see higher organisms, refuting those who like to treat genetics as the dominant variable in human diversity.
It's also astonishing to think its less than 60 years since Jane Goodall was chided for describing chimpanzees, our nearest relatives, as having individual personalities. Today we're recognizing something similar, if many times simpler, in single-celled organisms.