Jarmusch, S. A.; Schostag, M. D.; Yang, Z.; Wang, J.; Andersen, A. J. C.; Weber, T.; Ding, L.

Streptomyces are major players in soil microbiomes, however, interactions involving Streptomyces-Streptomyces are rarely described. The complex developmental cycle of Streptomycetes necessitates a multi-omics approach to unravel the web of information. This study resulted from the observation of induced sporulation between two environmental isolates from the same site, Streptomyces sp. P9-2B1 and Streptomyces sp. P9-2B2. When co-cultivated on potato dextrose agar (PDA), P9-2B2 induced a wave-like sporulation in strain P9-2B1. Using Mass Spectrometry Imaging, we revealed that a suite of lydicamycins, antibacterial NRPS-PKS hybrid metabolites, were present in this induced sporulation zone. Lydicamycin deficient mutants were generated using CRISPR-base editing and the inducible sporulation ceased, confirming their role in triggering morphological differentiation. In agar diffusion assays, pure lydicamycin was inhibitory when added concurrently with bacterial inoculation and induced sporulation with delayed addition. Subsequent testing of additional environmental isolates resulted in the same inducible sporulation wave phenomenon, including Streptomyces coelicolor M145 and M1146. We further evaluated the temporal production of the lydicamycins in monoculture over a 10-day time scale. On PDA, production was detectable upon sporulation at day 4 on PDA and peaked at day 9. On ISP2, lydicamycin production was minimal and stable over the 10 days, coinciding with a lack of sporulation. Using transcriptomics, we observed the upregulation of early aerial mycelium development four days into cocultivation and also the transitional genes responsible for development of spores on day 9. Along with these upregulated genes, we also observed numerous overall stress responses, specifically cell envelope stress responses. This finding uncovered Streptomyces-Streptomyces interactions mediated by lydicamycins, pointing to a potential role of certain groups of bioactive metabolites in nature.