How many bacteria does it take to replicate the Mona Lisa? About a million, give or take a few.
At least, that’s how many Escherichia coli cells scientists at Rome University genetically engineered to quickly swim and respond to light patterns in order to replicate Leonardo da Vinci’s masterpiece, according to a study published in eLife.
If it’s giving you a little bit of a WTF complex, rest assured they did so for a good cause. Controlling and manipulating bacteria with light – a process called photokinesis – means science could use them to build and transfer microscopic devices in the future.
E. coli are great swimmers. According to the researchers, they can move a distance 10 times their length in just a second. They propel themselves with a cellular motor, known as the flagellar motor, that works like an electric motor that requires energy to move – in this case that energy comes in the form of oxygen. Typically, the bacteria use their speed to help guide them to conditions for better growth or survival. In this case, the team genetically-modified E. coli cells to contain a protein called proteorhodopsin found in ocean-dwelling bacteria in order to make them respond to light. They intended to create little swimmers who picked up their pace when they received more light.
"Much like pedestrians who slow down their walking speed when they encounter a crowd, or cars that are stuck in traffic, swimming bacteria will spend more time in slower regions than in faster ones," said lead author Giacomo Frangipane in a statement. "We wanted to exploit this phenomenon to see if we could shape the concentration of bacteria using light."
The team set up a projector through a microscopic lens to see how E. coli changed their speed while swimming through areas with different amounts of light illuminated. They then took a negative image of the Mona Lisa and projected light onto it.
They suspected the slower swimmers receiving less light would group together, while the faster ones receiving more light would dart further apart. Just as predicted, the bacteria respond to the light visible through the negative by concentrating in the dark parts of the images and moving away from the illuminated ones.
Although they moved slowly, it took about four minutes for da Vinci’s painting to become visible, though blurred. To correct this, the researchers used a feedback loop that would compare the bacteria’s positions to da Vinci’s image every 20 seconds.
"We have shown how the suspension of swimming bacteria could lead to a new class of light-controllable active materials whose density can be shaped accurately, reversibly and quickly using a low-power light projector," said associate professor Roberto Di Leonardo. "With further engineering, the bacteria could be used to create solid biomechanical structures or novel microdevices for the transport of small biological cargoes inside miniaturized laboratories."