Stimulatory effects of bacitracin on sporulation and mycelial growth in thiostrepton-producing Streptomyces cyaneus ATCC 14921 and Streptomyces laurentii ATCC 31255

In a screening program for substances with morphogenic effects on the thiostrepton-producing Streptomyces cyaneus subsp. azureus and S. laurentii, bacitracin (BC) was found to have a remarkable growth-stimulating effect. The stimulatory effect on spore formation was so significant with about 5-fold increment in the number of spores and with striking elongation of the aerial mycelia in S. c. azureus and S. laurentii at 50 and 80 μg/ml, respectively. Also, BC markedly stimulated submerged mycelial growth after a long inhibitory lag period, accompanied by an increase in wet mass of the both species. These peculiar activities of BC on both streptomycetes were compared with its well-known biological and chemical activities. We speculated that the BC-induced stimulation of growth and sporulation might be due to its chelating and antimicrobial activities.