The approach of growing microorganisms in situ, or in a simulated natural environment is appealing, and different versions of it have been
described by several groups. The major difficulties with these approaches are that they are not selective for actinomycetes — a group of grampositive
bacteria well known as a rich source of antibiotics. In order to efficiently access actinomycetes, a trap for specifically capturing and
cultivating these microorganisms in situ has been developed, based on the ability of these bacteria to form hyphae and penetrate solid
environments. The trap is formed by two semi-permeable membranes (0.2–0.6 μm pore-size bottom membrane and 0.03 μm pore-size top
membrane) glued to a plastic washer with sterile agar or gellan gum inside. The trap is placed on top of soil, and filamentous microorganisms
selectively penetrate into the device and form colonies. Decreasing the size of the pores of the lower membrane to 0.2 μm restricted penetration of
fungi. The trap produced more filamentous actinobacteria, and a higher variety of them, as compared to a conventional Petri dish cultivation from
the same soil sample. Importantly, the trap cultivation resulted in the isolation of unusual and rare actinomycetes.
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