You probably have freaked out sometimes by seeing the mysterious pink streaks on toilet walls or bathtubs. But have you wondered what these are? In Biological Mysteries this is also a big question but with simple answer.
The answer is obviously a tiny microbe that loves to grow on wet surfaces. The bacterial biofilm is harmless unless you are immunocompromised (poor health). They dwell mostly in the presence of phosphorous or fatty acid like toilet soaps. If you inspect they do not grow well in summer season or during hot weather.
About the tiny stuff
The bacterium is Serratia marcescens and can grow between 5 to 40ºC which is quite wide. This is the same reason that they can grow everywhere. It prefers pH between 5 to 9, which is much significant as they prefer soapy waters. If you quickly wiki about this gram negative bacterium that will more freak you out as they are one of the known contenders for Hospital Acquired Infections. But in true sense that can only happen if you are immunocompromised and have increased risk if it reaches sterile parts of the body like lungs, brain or blood.
Behind these bacteria there lies a surprising story of its identification. Sometime in 1819, one Italian resident was frightened about the bloody pollen in humid summer. The family refused to stay at home as they were feared if it was caused by some evil spirits. Later several investigations have proved this to be bacteria that are enjoying their slimy bath.
Apart from the threat of nosocomial infection, it has proved to have anti-cancer property in the red pigment (called prodigiosin) but lots more still to be investigated.