Successful enrichment of the ubiquitous freshwater ac I A ctinobacteria

Summary Actinobacteria of the acI lineage are often the numerically dominant bacterial phylum in surface freshwaters, where they can account for > 50% of total bacteria. Despite their abundance, there are no described isolates. In an effort to obtain enrichment of these ubiquitous freshwater A ctinobacteria , diluted freshwater samples from L ake G rosse F uchskuhle, G ermany, were incubated in 96‐well culture plates. With this method, a successful enrichment containing high abundances of a member of the lineage acI was established. Phylogenetic classification showed that the acI   A ctinobacteria of the enrichment belonged to the acI ‐ B2 tribe, which seems to prefer acidic lakes. This enrichment grows to low cell densities and thus the oligotrophic nature of acI ‐ B2 was confirmed.