From the first page of the paper in question (Blount, Z. D., C. Z. Borland, and R. E. Lenski. 2008. Historical contingency and the evolution of a key innovation in an experimental population of Escherichia coli. Proceedings of the National Academy of Sciences, USA 105:7899-7906.) "They have since been propagated by daily 1:100
+
serial transfer in DM25, a minimal medium containing 25