Taxonomic studies on the snore surface morpholon, of micromonosporae

Abstract

Spore surface morphology of eight representative strains of micromonosporae were studied by transmission and scanning electron microscopy. Three main morphological types were observed: “smooth type”, “warty type” and “blunt spiny type”. The characteristic structures of these three types were found to be independent almost invariably on kinds of media used after more than 21-day incubation periods except some exceptions. Thus, electron microscopic method seemed to offer an important criterion in the classification of micromonosporae which exhibit little difference under light microscopic observation.
Subsequently this method was applied to the classification of 278 strains of micromonosporae isolated from soil samples collected in Japan and Uganda. Among them, smooth type and warty type strains were found with nearly equal frequency in soil samples from both regions, and sum total of strains belonging to these two types amounted to 70 to 80 per cent of the isolates. The intermediate type between smooth and warty type was also found with the frequency of about 10 per cent. Blunt spiny type micromonosporae appeared at very low frequency of 3to 5 per cent. Strains with spiny and hairy spore surface structures, known to occur frequently in streptomycetes, were not found among the micromonosporae strains used in this study.
Two strains each of micromonosporae which have the typical spore surface morphology described avobe, were used to study pathogenicity in mice. At 7 days after intravenous challenge, micromonosporae were isolated from internal organs, such as spleen, kidney, liver, etc.. However, the number of microorganisms in each internal organ decreased fairly rapidly, and most microorganisms had disappeared after 14 days in some cases and no changes in internal organs were observed with the naked eye. Additionally, as a result of observation of thin sections of each internal organ by microscopy, although slight inflammation was observed in some tissue samples, no remarkable change was observed in most samples. Therefore, it was judged that the micromonosporae used in this study have no pathogenicity in mice.