Humans not the major target of Shiga toxin

Dec 03, 2007

If you’ve survived Shiga toxin and the after-effects of food poisoning, you may have been the innocent victim of a battle for survival between predator and prey.

Bacteria that carry a virus (a bacteriophage) that packs the Shiga toxin gene (Stx) may depend on it for protection from bacterial predators like the ciliated protozoan Tetrahymena. This is small comfort if you’ve just consumed that.

Food poisoning victims -- as a result, for example, of consuming Shiga-packing E.coli in a contaminated bag of spinach -- have always had the cold comfort of being told that not all common bacteria make humans extremely sick, only the strains that have integrated the Shiga gene into their DNA. These bacteria can produce large amounts of the Shiga toxin and release it into the surrounding environment.

Leaving sick humans aside for a moment, Gerald Koudelka, Todd Hennessey, and colleagues from the University at Buffalo in Amherst, New York, wondered what evolutionary advantage the bacteria would derive from carrying around such a prickly viral hitchhiker. They hypothesized that the Stx gene might give the bacterial host an equalizer against bacterial predators.

“Humans may not be the major target of this toxin,” explains Koudelka. “Instead, they might be simply caught in the cross-fire in this ancient battle between prey and predators.”

To test their hypothesis, the researchers grew Tetrahymena with an E. coli strain (EDL933) that carries the Stx gene. It worked, at least, for the EDL933 that grew successfully in co-cultures with Tetrahymena. In this hostile environment, it was the predator, Tetrahymena, that was killed by the bacteria’s Shiga toxin. An E. coli strain (W3110) lacking Stx did poorly with Tetrahymena as roommates. The Tetrahymena had them for lunch.

The Shiga toxin kills by binding to a receptor on the surface of Tetrahymena. Adding protein subunits that block toxin binding to the protozoan predator prevented killing by Shiga toxin. Humans have the same surface receptor for Shiga toxin as do Tetrahymena, which gives biologists and produce packers a close interest in the deadly duel between Tetrahymena and Shiga-packing E. coli.

The Koudelka and Hennessey labs are continuing to characterize the route of Shiga toxin entry into the cytoplasm of Tetrahymena, its mode of killing, and the ability of Tetrahymena to develop resistance to Shiga toxin. The protozoan might make a model cellular system for Shiga detoxification, which one day might relieve some of the stress around the salad bar, say Koudelka and Hennessey.

Source: American Society for Cell Biology

Explore further: Best way to train farm dogs has lessons for all dog training

add to favorites email to friend print save as pdf

Related Stories

We are all made of stars

26 minutes ago

Astronomers spend most of their time contemplating the universe, quite comfortable in the knowledge that we are just a speck among billions of planets, stars and galaxies. But last week, the Australian astronomical ...

Netflix unveils new way to share recommendations

26 minutes ago

Netflix is giving its Internet video subscribers a more discreet way to recommend movies and TV shows to their Facebook friends after realizing most people don't want to share their viewing habits with large audiences.

How bubble studies benefit science and engineering

28 minutes ago

The image above shows a perfect bubble imploding in weightlessness. This bubble, and many like it, are produced by the researchers from the École Polytechnique Fédérale de Lausanne in Switzerland. What ...

How financial decisions are made

16 minutes ago

Jayant Kale didn't grow up dreaming of becoming a leading expert in corporate finance and mutual fund investment. But he's happy he invested in that market early in life.

Recommended for you

Migratory fish scale to new heights

40 minutes ago

WA scientists are the first to observe and document juvenile trout minnow (Galaxias truttaceus Valenciennes 1846) successfully negotiating a vertical weir wall by modifying their swimming technique to 'climb' ...

Computer simulations visualize ion flux

42 minutes ago

Ion channels are involved in many physiological and pathophysiological processes throughout the human body. A young team of researchers led by pharmacologist Anna Stary-Weinzinger from the Department of Pharmacology ...

Frequent fire and drying climate threaten WA plants

44 minutes ago

Murdoch University fire ecology experts have warned that in Western Australia's drying climate, many of the plant species which contribute to the stunning wildflower displays north of Perth may need 50 per ...

Neutron diffraction sheds light on photosynthesis

47 minutes ago

Scientists from ILL and CEA-Grenoble have improved our understanding of the way plants evolved to take advantage of sunlight. Using cold neutron diffraction, they analysed the structure of thylakoid lipids found in plant ...

User comments : 0