Fred Hoyle and Wickramasinghe have argued that microorganims fill up the whole of space. One finds dust and biological molecules between stars. Why not microorganisms? They assumed in one example, E. coli filling up interstellar space and then they calculated how much the absorption of light at different wavelengths from the E. coli model would be. They showed that the extinction curve i. e. absorption curve, was precisely followed for some infra red source. So their argument was that these micro organisms must exist.
His view on the issue of the cosmos being flooded by micro organisms. - Jayant Narlikar's Cosmology