Abstract
Multi-omics approaches, including metagenomics and single-
cell amplified genomics, have revolutionized our understanding
of the hidden diversity and function of microbes
in nature. Even in the omics age, cultivation is an essential
discipline in microbial ecology since microbial cultures are
necessary to assess the validity of an in silico prediction about
the microbial metabolism and to isolate viruses infecting bacteria
and archaea. However, the ecophysiological characteristics
of predominant freshwater bacterial lineages remain
largely unknown due to the scarcity of cultured representatives.
In an ongoing effort to cultivate the uncultured majority
of freshwater bacteria, the most abundant freshwater
Actinobacteria acI clade has recently been cultivated from
Lake Soyang through catalase-supplemented high-throughput
cultivation based on dilution-to-extinction. This method
involves physical isolation of target microbes from mixed populations,
culture media simulating natural habitats, and removal
of toxic compounds. In this protocol, we describe detailed
procedures for isolating freshwater oligotrophic microbes,
as well as the essence of the dilution-to-extinction culturing.
As a case study employing the catalase-supplemented
dilution-to-extinction protocol, we also report a cultivation
trial using a water sample collected from Lake Soyang. Of the
480 cultivation wells inoculated with a single lake-water sample,
75 new acI strains belonging to 8 acI tribes (acI-A1, A2,
A4, A5, A6, A7, B1, B4, C1, and C2) were cultivated, and each
representative strain per subclade could be revived from glycerol
stocks. These cultivation results demonstrate that the
protocol described in this study is efficient in isolating freshwater
bacterioplankton harboring streamlined genomes.
Citations
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