If you find it weird that your body, inside and out, is riddled with trillions upon trillions of bacteria, now imagine that all these microbes are teeny eyeballs, watching your every move. Well, that’s not far from the truth, according to a fascinating and borderline creepy new study.

Researchers from the University of Freiburg and Queen Mary University of London have found that certain photosynthetic microbes are like lenses, trapping and focusing light so they can sense where it’s coming from. This allows them to move towards the source and thus position themselves in the best spot to receive light for energy-making. Having been around for 2.7 billion years, they’re essentially the world’s smallest and oldest camera eyes, claim the researchers.

“I’ve been looking at cyanobacteria for my whole career,” lead researcher Conrad Mullineaux from Queen Mary told IFLScience. “Until we made this discovery by accident, it never occurred that they might be looking back! It made me think about them in a very different way. We may underestimate these small organisms, but they’re really very smart.”

The organisms the study looked at are called cyanobacteria, or more specifically a species called Synechocystis. Cyanobacteria are slime-formers that you’ll find pretty much everywhere in the environment. While you might take them for granted, as one of the world’s biggest producers of oxygen and gobblers of carbon dioxide, they’re as important to us as plants.

As photosynthetic organisms, they need to seek out light in order to generate energy in this manner. They can be seen twitching and gliding their way towards illumination, an ability known as phototaxis, but how do they perceive the direction in which it’s coming from? Turns out, they basically act as a microscopic eyeball, with the cell body as the lens and their inner membrane functioning as a retina.

^{The microbe's "vision" works in ways that aren't that fundamentally different to our own. Credit: eLife.}

Described in the journal eLife, when the spherical cell encounters directional illumination, a sharp image of the light is focused on the inside of the cell, at the opposite side to the source. This bright spot is then detected by specialized light-sensitive cells called photoreceptors, triggering a series of signals that ultimately result in the cell sending out hair-like structures called pili that help the organism crawl towards the light.

To get an idea of their “vision,” the team looked at the focused spot of light to work out the cell’s angular resolution, basically how well it can distinguish between two very close objects. For Synechocystis this was found to be about 21 degrees; paltry compared to our eye’s 0.02 degrees. That said, the researchers reckon it’s enough for them to take in fairly complex information and create a rudimentary 360-degree view of the surrounding environment.

“Obviously bacteria don’t think in the same way that we do,” said Mullineaux. “But if perception means having an apparatus to take in spatial information and respond to it appropriately, then I’d argue it’s not fundamentally different to the way we perceive. Everything is just on a much smaller scale.”

Hopefully, this study marks the beginning of an intriguing field of research; certainly, there are many questions to be answered. For instance, it seems plausible and likely that there are plenty of other bacteria out there that also act as lenses, but more work is needed to find out how widespread this phenomenon is.