RESULTS
A human presence in space, whether permanent or
temporary, is accompanied by the presence of
microbes. However, the response of
microorganisms to growth during a spaceflight
mission is not completely understood. While several
spaceflight studies have investigated changes in
microbial characteristics when cultured during
spaceflight, the Microbe experiment was the first to
investigate changes in virulence and gene
expression in several microbes that are pertinent to
both crew members and the general public on
Earth. The organisms investigated were, Salmonella
enterica, Salmonella Typhimurium, Pseudomonas
aeruginosa, and Candida albicans.Within a few hours after return to Earth aboard STS-115, the S. Typhimurium grown in space
was used to infect mice to determine the disease-causing potential (virulence) of the organism.
Mice infected with bacteria cultured in space displayed a decreased time to death and
increased percent mortality compared with those infected with ground controls (Wilson 2007).
To better understand why the spaceflight-grown cultures were more virulent, an analysis of the
gene expression was performed. The S. Typhimurium grown in space expressed a total of 167
genes differently compared to the identically grown cultures on Earth. Surprisingly, many genes
that are commonly associated with increased virulence were not differentially regulated.
Perhaps the most interesting finding was that a regulatory protein, Hfq, appeared to play a role
in the alteration in gene expression in response to spaceflight culture. This finding was the first
to identify a potential mechanism by which a microorganism was being altered when grown in
space. One additional finding detected alterations in microbial morphology grown during
spaceflight. Greater cellular aggregation and the formation of an extracellular matrix associated
with bacterial biofilms were displayed. Because extracellular matrix formation can help to
increase survival of bacteria under various conditions, this biofilm phenotype indicated a
change in bacterial responses that are related to increased virulence.
Also grown aboard STS-115 were cultures of P. aeruginosa (Crabbé 2011). A comparison of
spaceflight grown cultures to those grown identically on Earth indicated that 167 genes were
differentially regulated, with many being different than those seen with S. Typhimurium.
However, one key similarity was that when analysis of the data was performed, Hfq was again
identified as a key regulator for many of the differentially regulated genes. This finding
reinforced the role for Hfq in microbial response to spaceflight and also suggested that this
response may be evolutionarily conserved between species. The differentially regulated gene
expression data also indicated that many P. aeruginosa virulence characteristics may increase in
response to spaceflight culture. The results for C. albicans are still being evaluated and
prepared for publication.
Candida albicans. Dennis Kunkel Microscopy Inc
image.