Salmonella Spills Its Secrets On Shuttle
of Article: http://www.space-travel.com/reports/Salmonella_Spills_Its_Secrets_On_Shuttle_999.html
Dr. Tony Phillips
Huntsville AL (SPX) May 07, 2009
Salmonella, what's gotten into you? Researchers have been asking themselves
this question ever since Salmonella bacteria grown on board the space shuttle returned to Earth 3 to 7 times more virulent
than Salmonella grown on the ground under otherwise identical conditions.
out why could help safeguard astronauts from disease and lead to new treatments for
food poisoning and other common ailments on Earth.
research by Cheryl Nickerson (Arizona State University) and colleagues
explains not only why Salmonella gets "revved up" in space, but
also how to calm it down again.
think space travel tricks Salmonella into behaving as if it is in the human
gut," Nickerson says. "It's a mechanical phenomenon having to do
with 'fluid shear.'"
microbes have the ability to sense the force of fluid moving past their
outer surfaces. This "fluid shear" acts as a signal to the
microbe, helping it to know where in the human body it's located.
Salmonella usually enters the body by hitching a ride on food that a person
middle of the tube-shaped intestines, the liquid-like mixture of
half-digested food and digestive juices churns around quite a bit, so the
amount of fluid shear is high.
But as a
Salmonella cell approaches the wall of the intestines, it slips into the
tiny spaces between microscopic, hair-like protrusions called microvilli
that cover the intestinal lining. There, the cell becomes sheltered from
the churning motion, and fluid shear drops to very low levels.
there that the bacterial cell can cross from the intestines into the bloodstream
to start an infection. So it would make sense for a bacterium experiencing
low fluid shear to alter the activity of genes that help the bacterium
survive and cause infection.
simulations have shown that the amount of fluid shear experienced by
bacteria in the weightless environment of orbit is similar to the amount in these
tiny spaces at the intestinal wall, Nickerson says. "Space flight is a
low fluid shear environment."
team looked at Salmonella from two shuttle flights to the International
Space Station: STS-115 in Sept. 2006 and STS-123 in March 2008. They found
that 167 genes were either more or less active in these keyed-up bacteria
than in the bacteria that hadn't flown.
also identified a "master switch" that regulates about one-third
of these genes, a protein called Hfq. Activity of this protein was also
affected by the low fluid shear conditions of spaceflight.
scientists know which genes and proteins help create this
virulence-boosting effect, they are working to use this information to
develop new strategies to combat Salmonella food-borne illness, such as
vaccines and therapeutics.
has already found one promising way to combat Salmonella's extra virulence:
add a dash of ions. When Nickerson and her colleagues grew the same strain
of bacteria in a culture medium that contained higher concentrations of
five ions - potassium, chloride, sulfate, magnesium, and phosphate - the
virulence of the bacteria due to spaceflight no longer went up!
are funny things," Nickerson says. "If you give them too much or
too little of something they're used to having around, they'll surprise you
with how they respond."
turns out, many of the genes activated by the low fluid shear environment
of spaceflight are involved in transporting these ions in and out of the
cells, so there could be a connection. Research on this ion effect is still
ongoing, Nickerson says, but she speculates that it could eventually lead
to new ways to use these ions to ward off Salmonella infections.
question people ask me is, 'Why in the world did you think of looking at
[Salmonella in space]?' I turn that around and ask, 'Why would you not
think of it!'" Nickerson says. "Whenever scientists have studied
microbes under extreme conditions, we have found amazing new insights into
how they function. Space flight is another extreme environment that's
me it was a no-brainer."