SPACE STATION BUGS. “The presence of several microorganisms has been studied in the Russian Mir Space Station as well as the International Space Station. The organisms consist of both bacteria and fungi, and are exposed to about 4 cGy of ionizing radiation per year. Many bacteria and fungi in these environments have been found to be pigmented or melanized.”
https://royalsocietypublishing.org/doi/10.1098/rsif.2016.0459