Microgravity Ups Bacterial Virulence. (September 25, 2007)

 According to the Wikipedia entry: "The ISS has been, as of today, far more expensive than originally anticipated. The [European Space Agency] estimates the overall cost from the start of the project in the late 1980s to the prospective end in 2010 to be in the region of €100 (A$163) billion."

From a scientific viewpoint the question has been raised repeatedly to what use will it be put.

With an online report this week in the Proceedings of the National Academy of Sciences microbiologist Cheryl Nickerson and her colleagues at Arizona State University may have found one possible reason, although the 24-hour experiment was conducted in micro-gravitational conditions on board the space shuttle Atlantis during the 12 day flight in September 2006 rather than on the ISS.

The bacterium Salmonella typhimurium grown aboard the shuttle came back three times more virulent than controls kept on Earth under conditions as identical as possible except they were grown under 1G. Virulence was based on the so-called LD₅₀, the dose required to kill 50% of mice in a study population.

According to Dr Nickerson: "The space-flight environment imparts a signal that can induce molecular changes in bacterial cells."

The comparative analysis of the two cultures -- S. typhimurium cultured at 0G and 1G -- showed differences in the expression levels of 167 genes, and the concentrations of 73 proteins. It's suggested that one particular protein, Hfq -- which is known to regulate RNA synthesis and have a role in bacterial virulence on Earth - may be responsible for the increase in virulence.

The PNAS paper suggests that the changes observed could be brought about by a reduction in 'fluid shear' — the movement of liquid around the bacteria. Previous microgravity studies on Earth using culture media with low shear coefficients  have also increased Salmonella virulence. Dr Nickerson has been interested in the effects of low sheer environments but in Earth gravity for several years.

She says: "A lot of our knowledge has come from testing cells at extremes. It's exciting that this research can help crews stay healthy as they push the boundaries of manned space flight. What's equally exciting is the potential this research holds to improve health on Earth."

And Jörg Vogel, a researcher at the Max Planck Institute for Infection Biology in Berlin says: "Space flight at the moment is rare for human beings. Looking 20 years ahead, I think about the companies that are going to offer flights for tourists; we'll have tonnes of people flying to space. Those people will inevitably carry lots of bacteria. We don't know how these bacteria will behave in those conditions."

[Note added September 27, 2007 -- According to Nobel-prize-winning particle physicist Steven Weinberg: "The International Space Station is an orbital turkey."]