Microbial Dark Matter and the Search for Life on Earth

In discussions of contamination risk on Mars, it’s sometimes taken as a given that any microbes we accidentally introduced into a Martian ecosystem would be easy to distinguish from any relic life that existed there. This claim touches on the very interesting question of what kinds of life we can identify on Earth. As early as 1932, the Soviet microbiologist A.S. Razumov noticed that there were far more bacteria visible under a microscope in water samples than could be persuaded to grow in his laboratory. In a 1985 paper, the researchers Staley and Konopka christened the discrepancy ‘The Great Plate Count Anomaly’. By their estimate, something like 99% to 99.9% of bacteria in freshwater samples were happy, metabolically active microbes who could not be bullied or bribed into growing on a Petri dish or in a vial of liquid medium.Back in an era when culturing microbes was the first step in trying to understand them, this was a problem. The only thing researchers could do was cross their…