Effect of medium composition on the culturability of bacteria from Zwischenahner Meer (May sample). SF, synthetic freshwater buffered with HEPES. YPG medium containing yeast extract (0.2%), peptone (0.1%) and glucose (0.2%). SF+YPG, synthetic freshwater containing yeast extract, peptone, glucose at low concentrations (see Section 2). Asterisks denote values which differ significantly from culturability in R2A (P<0.01).