Glow Squid

Biologists have discovered how this Hawaiian bobtail squid glows from its belly.  Surprisingly, the two-inch-long animal acquires this ability by sequestering bacteria that produce the toxic molecule responsible for whooping cough and gonorrhea in humans.

"If you deprive the animal of those microbes, the system doesn't develop," said Margaret McFall-Ngai from the University of Wisconsin at Madison.

The molecule, tracheal cytotoxin, which is made by different sorts of bacteria, initially kills certain squid cells.  This, however, allows the formation of a chamber that serves as a permanent home for the bacteria inside the squid. In this way, both squid and bacteria benefit from the relationship. 

While foraging at night for shrimp, the squid's subtle light blends in with moonlight - thus hiding the animal from its predators that lurk on the ocean floor. 

The fact that certain bacteria can be helpful to some organisms - while harmful to others - is reason for questioning the widespread, sometimes indiscriminate, use of antibiotics, said McFall-Ngai, senior author of a recently published paper on these findings in Science.

-- Michael Schirber

Credit: William Ormerod