Astronauts of the future may have a new foe to contend with: space bacteria. Scientists have found that Pseudomonas aeruginosa, a common contaminant of medical equipment and a cause of urinary tract infections, among other diseases, grows better in zero gravity than it does on Earth, even when starved of nutrients. The researchers grew the microbes in simulated urine both in an Earth-bound lab and onboard the space shuttle Atlantis (experimental setup shown) in July 2011. In some of the samples, the team dramatically reduced the concentrations of dissolved phosphate and oxygen to simulate conditions that might exist inside equipment used to recycle urine into water on spacecraft during long-duration flights. When nutrients were plentiful, the growth rates of the bacteria in zero-g conditions—and particularly, the concentrations of cells after 72 hours—were the same as those grown in the lab under normal conditions. But in samples with lower concentrations of phosphate and oxygen, the Earth-bound bacteria didn’t grow as quickly as they did when fully nourished, while those cultured in microgravity grew as prolifically as those provided with a full complement of nutrients, the researchers report online today in BMC Microbiology. Reasons for the disparity aren’t clear, the researchers say, but results suggest that bacteria introduced to space stations and spacecraft by people, given enough time, might grow to reach greater concentrations than they do in similar conditions on Earth, even if starved of nutrients. Besides helping scientists better understand the risks of P. aeruginosa colonizing equipment on spacecraft or causing diseases such as urinary tract infections among astronauts, the experiments may improve scientists’ ability to predict whether other species of bacteria might become more virulent in space.