[Electron microscopic study of active and inactive variants of Proactinomyces (Nocardia) mediterranei, a producer of rifamycin B].

Four mutants of Proactinomyces (Nocardia) mediterranei, an organism producing rifamycin B were subjected to electron microscopic investigation. The mutants differed in the biosynthetic activity. The investigation showed correlation between the length of the hyphal fragments of the over-substrate mycelium and the level of the organism activity.

[Biosynthesis of the labelled rifamycin B in the presence of different 14C- and 3H-precursors].

The results of studying the effectiveness of incorporation of the label from different 14C- and 3H-precursors into the molecule of rifamicin B during its biosynthesis are presented. The regularities of the label incorporation into the antibiotic composition as dependent on the time of the precursor addition were investigated. A radiochemically pure preparation of 14C-rifamicin B with specific radioactivity of 3 mcurie/mg was obtained.

[Effect of formaldehyde on a Pseudomonas fluorescens strain].

The strain of Pseudomonas fluorescens was isolated from active ooze and was capable of growth on a medium containing 100 mg/litre of formaldehyde. As a result of stepwise selection, a variant of Ps. fluorescens 27 oxidizing 250 mg/litre of formaldehyde was obtained.

[Variability in Act. circulatus var. monomycini induced by N-5-nitroso-N-methylbiuret].

The effect of N-5-nitrozo-N-methylbiuret (NMB) on various features of Act. circulatus var. monomycini, an organism producing monomycin was studied.