A PCR condition was established to distinguish strains of Actinobacteria from both Gram-negative bacteria and Gram-positive bacteria with low G+C content of DNA by taking advantage of a stable, specific and common insertion of a 100 bp sequence in the domain III of the 23S ribosomal RNA gene of class Actinobacteria. The PCR was designed to amplify a 380 bp fragment from Actinobacteria and a 270 bp fragment from the above bacteria. PCR-based survey of known strains as well as newly isolated soil bacteria confirmed that this PCR worked well to select Actinobacteria. In the survey it was unexpectedly found that several strains provided both 270 bp and 380 bp amplified fragments (the sequences of these two fragments obtained from Agrococcus jenensis were determined), indicating the presence of at least two copies of the domain III of the 23S rDNA gene.
Actinomycetes were isolated from live plants collected in Toyama and Miyagi prefectures, Japan. Three hundred and ninety eight actinomycete strains were obtained from the leaves, stems and roots of 11 harbaceous and 13 arbor plants of agricultural and wild species. n-Butanol extracts of the fermentation broths of these strains were screened for antiphytopathogenic activity using in vitro antimicrobial and in vivo antiinfective assays. About 10–20% of the extracts showed antagonistic activity against fungal or bacterial plant pathogens. In addition, several extracts suppressed the infection of Alternaria brassicicola TP-F0423, a fungal pathogen to seedlings of Chinese cabbages in vivo.
New plant growth inhibitors, substances A-79197-2 and -3, were found to be produced by strain SANK 61299 isolated from fresh plant leaves. Strain SANK 61299 was identified as Dacthylosporangium aurantiacum. Substances A-79197-2 and -3 were determined to be di- and tri- saccharides of streptol, an active ingredient, respectively. Streptol related compounds have been found as components of plants.