Microwave irradiation is a useful tool for improving isolation of actinomycetes from soil.

Actinomycetes are an important source of novel, biologically active compounds. New methods need to be developed for isolating previously unknown actinomycetes from soil. The objective of this experiment was to study microwave irradiation of soil as a means for isolating previously unknown actinomycetes. Soil samples were collected at ten elevations between 800 and 3670 m on Taibai Mountain, Shaanxi Province, China. Moistened soil samples were irradiated at 120 W heating power (2450 MHz) for 3 min using a household microwave oven. Irradiation increased total actinomycete, streptomycete, and antagonistic actinomycete counts on three types of culture media. Irradiation also increased the number of culturable actinomycete isolates. Some actinomycete isolates were culturable only after the soil was irradiated, whereas other isolates could not be cultured after irradiation. Irradiation of soil from elevations > 3000 m increased actinomycete counts significantly but had little effect on the number of culturable actinomycete isolates. In contrast, irradiation of samples from elevations < 3000 m had relatively little effect on actinomycete counts, but significantly increased the number of culturable actinomycete isolates. We used 16S rDNA sequence analysis to identify 14 actinomycete isolates that were only culturable after irradiation. Microwave irradiation of soil was helpful for isolating Streptomyces spp., Nocardia spp., Streptosporangium spp., and Lentzea spp. Slightly more than 90% of the identified actinomycete species were biologically active. In conclusion, microwave irradiation is a useful tool for isolating biologically active actinomycetes from soil.