In the submerged cultivation of filamentous microbes, including actinomycetes, complex morphology is one of the critical process features for the production of secondary metabolites. Ansamitocin P-3 (AP-3), an antitumor agent, is a secondary metabolite produced by Actinosynnema pretiosum ATCC 31280. An excessive mycelial fragmentation of A. pretiosum ATCC 31280 was observed during the early stage of fermentation. Through comparative transcriptomic analysis, a subtilisin-like serine peptidase encoded gene APASM_4178 was identified to be responsible for the mycelial fragmentation. Mutant WYT-5 with the APASM_4178 deletion showed increased biomass and improved AP-3 yield by 43.65%. We also found that the expression of APASM_4178 is specifically regulated by an AdpA-like protein APASM_1021. Moreover, the mycelial fragmentation was alternatively alleviated by the overexpression of subtilisin inhibitor encoded genes, which also led to a 46.50 ± 0.79% yield increase of AP-3. Furthermore, APASM_4178 was overexpressed in salinomycin-producing Streptomyces albus BK 3-25 and validamycin-producing S. hygroscopicus TL01, which resulted in not only dispersed mycelia in both strains, but also a 33.80% yield improvement of salinomycin to 24.07 g/L and a 14.94% yield improvement of validamycin to 21.46 g/L. In conclusion, our work elucidates the involvement of a novel subtilisin-like serine peptidase in morphological differentiation, and modulation of its expression could be an effective strategy for morphology engineering and antibiotic yield improvement in actinomycetes.

High temperatures deleteriously affect cells by damaging cellular structures and changing the behavior of diverse biomolecules, and extensive research about thermophilic microorganisms has elucidated some of the mechanisms that can overcome these effects and allow thriving in high-temperature ecological niches. We here used functional genomics methods to screen out a cold-shock protein (CspL) from a high-productivity lactate producing thermophile strain ( Bacillus coagulans strain 2-6) grown at 37°C and 60°C. We subsequently made the highly striking finding that transgenic expression of CspL conferred massive increases in high temperature growth of other organisms including E. coli (2.4-fold biomass increase at 45°C) and the eukaryote S. cerevisiae (a 2.7-fold biomass increase at 34°C). Pursuing these findings, we used bio-layer interferometry assays to characterize the nucleotide-binding function of CspL in vitro , and used proteomics and RNA-Seq to characterize the global effects of CspL on mRNA transcript accumulation and used RIP-Seq to identify in vivo RNA targets of this nucleotide-binding protein (e.g. rpoE , and rmf , etc.). Finally, we confirmed that a nucleotide-binding-dead variant form of CspL does not have increased growth rates or biomass accumulation effects at high temperatures. Our study thus establishes that CspL can function as a global RNA chaperone.