The bobtail squid may pretend he's just cooperating with those light-emitting bacteria, but is something more ominous going on? Let's check in with Margaret McFall-Ngai, a biologist at the University of Hawaii.
She says that while symbiotic (defined) relationships between luminescent bacteria and animals are nothing new, there's some evidence that the bacteria are getting a raw deal.
So is this may be less a case of symbiosis than of slavery. The squid, she observes, "inhibits the growth of the bacteria to enhance their luminescence." And the bacterium could make a better living drifting in the ocean, or in the gut of another marine animal, she observes.
In this ventral cross-section of Euprymna Scolopes, the symbiotic light-emitting "photophore" is the black and silver, two-lobed structure in the center. Courtesy of Margaret McFall-Ngai.
The idea of enslaved bacteria has raised some eyebrows among microbiologists, but it's worth thinking about, McFall-Ngai says, since it helps us broaden our perspective on life, and demonstrates how important bacteria are to life processes.
Particularly
imperiled paradigms
The simplest way to explain that relationship is that it's not simple at all. Most people, if they happen to think about bacteria at all, conjure up disease and decay. In fact, most people would be dead without bacteria, observes McFall-Ngai, since the little critters play essential roles in producing vitamins and preventing disease. (Since the bacteria in our guts outnumber the cells in our bodies, it's just as well that they're helpful!)
Nevertheless, and for understandable reasons, bacteriologists have traditionally focused on disease-causing organisms, and, for simplicity, on one species of bacterium at a time. But that skews our view of how bacteria actually live, says McFall-Ngai.
From her work with the bobtail squid, in collaboration with Ned Ruby, also of University of Hawaii, she's learning that complexity and subtlety may be more important than brute force in explaining what's going on.
The window into complexity was opened by the fact out V. fischeri is closely related to V. cholerae, which causes the human intestinal disease, cholera.
Cholera is caused by a toxin released by V. cholera, and it's curious that the light-emitting bacterium produces a similar toxin. But instead of harming the poor little bobtail, the toxin seems to signal it to secrete food for the bacterium-- a kind of chemical "dinner bell."
And this raises this intriguing -- and still unproven -- notion: that when a cholera bacterium secretes toxins, it's trying not to kill its host but to discuss the menu. If so, then our whole notion of pathogenesis (defined) may need rewriting, McFall-Ngai suggests. "Maybe when we've been studying cholera pathogenesis we've been studying an aspect of a normal conversation that's gone wrong."
Indeed, the pure-culture approach, which focuses on the pathogen, may cause other misunderstanding. "It's like trying to understand the complexity of all the cultures that lived in Paris by studying the activity of the Nazi occupiers," McFall-Ngai suggests. "You are studying groups that don't belong there, and have disrupted the normal activities." For more, see "Studies of the Symbiotic Relationship..." in the bibliography.
If you missed our coverage of high-temperature bacteria, there's still a chance to return.
Otherwise, in case you were thinking that the "flashlight squid" was the only strange thing beneath the waves, click again.
Actually, McFall-Ngai is not an advocate for the liberation of Vibrio fischeri (the light-emitting bacterium that helps bobtail squid evade predators). She studies their interaction with the bobtail squid as a way of understanding the broader issue of the relationship between bacteria and animals.
