What they actually said was "This is the smallest a cell can be and still accommodate enough material to sustain life" - this was shortened in the lede. But "a

What they actually said was "This is the smallest a cell can be and still accommodate enough material to sustain life" - this was shortened in the lede. But "as small as life can get" is a thing that has been studied, eg for Mars Sample-Return missions, they have to figure out a safe filter size (chapter 3): http://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Mars_Sample_Return_backward_contamination_study.pdf http://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Ma... An important distinction is whether these organisms can live 'independently' - a virus relies on a host. Quoting from the doc above: it is believed that theoretically a coccoid[1] cell with the minimum number of genes to be free living in an environment other than a living host would have a minimum cell diameter of approximately 0.15–0,2 μm. - which is around about the size of the beasties in the parent article. They did consider smaller biological entities though, like gene transfer agents[2], and recommended filters such that nothing over 0.05μm is released under any circumstances, and that there's only a 1 in a million chance of anything smaller than 0.01μm escaping. [1] Spherical. http://en.wikipedia.org/wiki/Coccoid http://en.wikipedia.org/wiki/Coccoid [2] http://en.wikipedia.org/wiki/Gene_transfer_agent http://en.wikipedia.org/wiki/Gene_transfer_agent