This microbe turns into a cannibalistic ‘Hulk’

A newly discovered microbe is like a mini version of the Hulk.

Euplotes gigatrox is a single-celled protist that resembles an insect. It grazes on bacteria and other tiny microbes. Sometimes a small number of the protists balloon into “supergiants” more than twice their regular size. The huge cells cannibalize their smaller, genetically identical brethren. The triggers for the change aren’t entirely clear, but it tends to happen when there is plenty of food, researchers reported May 14 in the Proceedings of the National Academy of Sciences.

The transformation happens in stages, says Ben Larson, a cell biologist at Rensselaer Polytechnic Institute in Troy, N.Y., who discovered the microbes in gunk scraped from an aquarium filter in Curaçao.

First, “a cell gets a big mouth, and they start running around like crazy,” Larson says. At that stage they aren’t very good at cannibalism, but if a would-be Hulk manages to capture one of its siblings or cousins in its enlarged mouth, “the body plan of the cell rescales, and they grow up to be these just enormous cannibalistic supergiants.”

And like Bruce Banner and the Hulk, the giants and the regular-size cells behave differently. Besides the cannibalism, the big cells walk in circles and no longer swim like smaller cells can.

Giants can return to their former size by dividing asymmetrically. The Hulks can produce nine normal-size offspring each in a 24-hour period and up to 16 in 120 hours. Normal size E. gigatrox divide just once in 24 hours. With each lopsided division the giant cells shrink until they are back to normal size and behavior.

Up to 42 percent of the organism’s genes are involved in the transitions from regular size to supergiant and back again, Larson and colleagues found. Learning how the protists transform may help researchers understand how simple organisms can develop complex behaviors, and perhaps how multicellular life evolved.