When the Shuttle returned, the team recovered the space-bound bacteria and analysed the pattern of genetic activity across their entire genomes using microarrays. This modern and powerful technique allows scientists to measure the activity of thousands of genes at the same time. The researchers also measured the levels of every protein in the samples.
The team looked at the entire Salmonella genome and found that the expression of 167 genes and the levels of 73 proteins had changed in the space-travellers. Clearly, the environmental changes of space-flight had triggered changes in the bacteria at the molecular level.
When fed to mice, the altered bacteria were three times more virulent than their Earth-bound counterparts. The infected mice succumbed to much lower concentrations of space-faring bacteria and in much shorter times.