In the last mission of the Atlantis ferry, the bacterium Salmonella typhimurium has been transferred to space. Specimens of bacteria that have returned to the ground are far more lethal than the original ones; one-third of the normal amount is enough to kill laboratory mice. According to scientists, this is due to microgravity, a situation in which the flow of bacterial fluid is more difficult than on Earth, to which bacteria have been adapted by molecular changes. The changes have made the bacteria more lethal.