A method for the selective isolation of Microtetraspora glauca and related four‐spored actinomycetes from soil

An effective plate culture method for the isolation and enumeration of four‐spored actinomycetes belonging to the Microtetraspora glauca group of Thiemann et al. is described, in which a water suspension of a soil sample given dry heat (110°C, 1 h) is subjected to a treatment with 0·05% benzethonium chloride (BC) and cultured on the new medium LSV‐SE agar which is supplemented with kanamycin, norfloxacin and nalidixic acid. The LSV‐SE agar, based on a commercial lignin (dealkaline; 1 g 1 ‐1 as the major carbon source, specifically supported adequate growth and good sporulation for the M. glauca ‐group species, thus facilitating the detection and enumeration of this rare actinomycete group in the sample. The addition of the antibacterial agents to the LSV‐SE agar, as well as the dry heat and BC treatment, provided a selective effect of reducing the nonfilamentous bacteria and undesirable actinomycetes associates occurring on the isolation plates. A total of 26 different natural samples were examined. From 18 samples (16 of field and forest soils, and two of stream and lake sediments), the new method consistently achieved the selective isolation of the M. glauca group, which accounted for 2–27% of the total population recovered. Definite evidence of biological activity which degrades the grass lignocellulose was found in all of the 39 test M. glauca ‐group isolates. Of these, 14, or 36%, possessed antimicrobial activity.