The Crawling Eye: Cells as Lenses

Certain bacteria can respond to light be turning their whole bodies into eyeballs.

The cells are round anyway; why not focus light? Scientists have wondered why certain cyanobacteria in “pond slime” are able to move toward light, a process given the name phototaxis (“light order”). A new study published in eLife suggests that the whole cell becomes a lens. The BBC News comments:

Despite being just three micrometres (0.003mm) in diameter, the bacteria in the study use the same physical principles as the eye of a camera or a human.

This makes them “probably the world’s smallest and oldest example” of such a lens, the researchers write in the journal eLife.

Scientists had noticed photo taxis for a long time. Reporter Jonathan Webb writes, “After more than three centuries of scientists eyeballing bugs under microscopes, Prof Mullineaux said it was remarkable that nobody had picked up on this before.” A press release from the University of Freiberg sheds some light on that:

All previous attempts to explain bacterial phototaxis, the process by which bacteria move toward light, have failed because these organisms, which measure only a few lengths of a light wave, were thought to be too small to perceive differences in light between the front and back side of the cell. Since the entire bacterium functions like a lens, however, the organisms can concentrate light, creating a pronounced light gradient within the cell.

It’s not that different from the way the human eyeball focuses light, Live Science says. “A cyanobacterium, however, is 500 million times smaller than the human eye, and the algae likely view only the blurry outlines of objects that the human eye could see clearly, the researchers said.” In response to the light, a cyanobacterium grows tiny tentacles called pili that move the cell toward the light source.

What’s also remarkable is that none of the articles or the journal paper itself talked about evolution.

Think about what a cell needs to use this information. It has to know how to shape itself into a lens. There have to be receptors at the focal point. Those receptors have to send signals to the nucleus, where genes must be transcribed to turn the information into action. The cell has to grow pili at the right place, and move them in directions that push the whole cell toward the light.

If any one of those processes is missing (and each involves complex molecular machinery), phototaxis wouldn’t work. That’s design, not evolution. That this takes place in a “simple, primitive” life form like a bacterium should give Charlie more cold shudders.