The aromatic polyketide antibiotic oxytetracycline (OTC) is produced by Streptomyces rimosus as an important secondary metabolite. Enhancement of self-resistance is one effective way to improve antibiotic production in Streptomyces spp. In the present study, we aimed to improve the production of OTC by introducing extra copies of the OTC resistance genes, otrA and otrB, into the chromosome of the industrial strain of S. rimosus (SRI). First, otrA and otrB were cloned and ligated with pSET152 to generate the recombinant plasmids pSET152-otrA/otrB, the demethylated pSET152-otrA/otrB by Escherichia coli ET12567(pUZ8002) were then introduced into SRI to yield otrA/ otrB knock-in mutants: SRI-A (otrA) and SRI-B (otrB). Ten selected mutants and the parent SRI strain were cultured in shake flasks. Production of OTC was increased by 67% in one SRI-B mutant compared with the parent strain, suggesting that the enhancement of resistance gene otrB in the antibiotic producer is an effective way to improve OTC biosynthesis. However, introduction of extra copy of otrB could retard growth of mutant cells.
Introduction of Extra Copy of Oxytetracycline Resistance Gene otrB Enhances the Biosynthesis of Oxytetracycline in Streptomyces rimosus
In order to monitor the operation status of distribution network in real time and ensure the security and stability of distribution internet of things, a fault monitoring method based on fuzzy association rule mining was proposed. Fuzzy association rules mining was used to build the normal state parameter model of distribution network. The degree of interest index replaced the traditional index, aiming to improve the association degree between the rule parameters and form an effective expert knowledge base. According to the rules in the expert knowledge base, the normal state data of distribution network were obtained by fuzzy reasoning. Further, the state similarity function between the monitoring states and the normal states was used as the state judgement index. When the similarity is lower than the threshold, the fault alert should be triggered. Taking the single-phase ground fault data of distribution network simulated by MATLAB Simulink as an example, it was verified that the proposed method can effectively monitor the single-phase ground fault.
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