Is a single colony “pure”?

Shrestha et al. find that a contaminating strain of Geobacter sulfurreducens persists even after repeated streaking of single colonies on solid media. The stowaway strain KN400 was not found by deep sequencing, and was discovered only when it presented a phenotype of interest many years after the “isolation” of the DL1 strain. This finding calls into question the (common) assumption that a single colony arises from a single progenitor cell and is genetically “pure” and homogeneous for the purposes of microbiological experiments. -CMJ


Shrestha PM, Nevin KP, Shrestha M, Lovley DR. 2013.

When is a microbial culture “pure”? Persistent cryptic contaminant escapes detection even with deep genome sequencing. mBio 4(2):e00591-12. doi:10.1128/mBio.00591-12.