Analysis of secondary metabolites and morphology in Streptomyces rimosus microparticle-enhanced cultivation (MPEC) at various initial organic nitrogen concentrations

The influence of talc microparticles on metabolism and morphology of S. rimosus at various initial organic nitrogen concentrations was investigated. The shake flask cultivations were conducted in the media with yeast extract (nitrogen source) concentration equal to 1 g YE L^{- 1} and 20 g YE L^{- 1}. Two talc microparticle concentrations of 5 g TALC L^{- 1} and 10 g TALC L^{- 1} were tested in microparticle-enhanced cultivation (MPEC) runs. A high nitrogen concentration of 20 g YE L^{- 1} promoted the development of small agglomerates (pellets) of projected area lower than 10⁵ µm² and dispersed pseudohyphae. A low nitrogen concentration of 1 g YE L^{- 1} led to the limitation of S. rimosus growth and, in consequence, the development of the smaller number of large pseudohyphal agglomerates (pellets) of projected area higher than 10⁵ µm² compared to the culture containing a high amount of nitrogen source. In both cases talc microparticles were embedded into pellets and caused the decrease in their sizes. The lower amount of talc (5 g TALC L^{- 1}) usually caused the weaker effect on S. rimosus morphology and metabolite production than the higher one. This correlation between the microparticles effect on morphology and metabolism of S. rimosus was especially noticeable in the biosynthesis of oxytetracycline, 2-acetyl-2-dicarboxamide oxytetracycline (ADOTC) and spinoxazine A. Compared to the control run, in MPEC their levels increased 4-fold, 5-fold and 1.6-fold respectively. The addition of talc also improved the production of 2-methylthio-cis-zeatin, lorneic acid J and milbemycin A₃.