| Summary: | Abstract Biosynthesis of secondary metabolites in actinobacteria is regulated by complex regulatory mechanisms on responding environmental changes. In this study, we have identified a two-component system (TCS) designated as RimA1A2 in the genome of Streptomyces rimosus M4018, with high homology to the TCS RapA1A2 from Streptomyces coelicolor, known for its positive regulatory function towards actinorhodin (ACT) biosynthesis. Using RT-PCR analysis, we demonstrate that rimA1 encodes response regulator (RR) and rimA2 encoding histidine kinase (HK) from S. rimosus that are co-transcribed as a single-polycistronic mRNA. When S. rimosus was cultivated on standard media, no significant difference in culture growth or morphological properties was observed between the rimA1-disrupted mutant and parent strain M4018. However, the rimA1-disrupted strain displayed significant increase in oxytetracycline (OTC) titer when cultivated in minimal medium (MM) containing glycine as sole nitrogen source, and the transcription of selected genes involved in OTC biosynthesis was increased, supporting the hypothesis that RimA1A2 has a negative regulatory role in OTC biosynthesis via global regulation. We observed an increased resistance of the rimA1-disrupted mutant strain to selected antibiotics. Interestingly, in the rimA1-disrupted strain, OTC biosynthesis was affected under different environmental stress conditions such as osmotic and oxidative stress. Accordingly, this phenotype was observed in a medium-dependent manner. Considering complexity of regulatory networks in antibiotic-producing organisms, this study demonstrates the importance of cultivation conditions, which is often neglected.
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