Phenotypical divergences between populations of soil bacteria isolated on different media

Bacterial strains were randomly isolated from soil using three different media with glucose (TG), Tryptone Soya Broth (TTS), and succinate (TS) as carbon sources. Plate counts obtained were 12.0×10⁷, 4.5 ×10⁷, and 1.5×10⁷ g^–1 soil dry weight, respectively. The strains were characterized phenotypically by the API 20B test system. A cluster analysis of all isolates revealed 40 biotypes at 80% similarity, 23 in TG, 29 in TTS, and 27 in TS. Each of the 10 most common biotypes contained 10 to 2.5% of the isolates, and 17 biotypes contained one or two isolates. The common biotypes were unevenly distributed among the isolates from the different media. About 20% of the isolates from TG and TTS were unique for the particular medium, whereas among the isolates from TS, about 60% were unique. Thirty percent of the isolates belonged to biotypes that were common to all three populations. All media gave approximately the same high diversity measured as Shannon index and Equitability, indicating no direct correlation between plate count and diversity.