To enhance the ε-poly-l-lysine (ε-PL) productivity of Streptomyces sp. FEEL-1, a novel breeding strategy of atmospheric and room temperature plasma (ARTP) mutagenesis with streptomycin resistance screening was developed. After three rounds of recursive breeding, one strain designated AS3-14 was selected with a ε-PL yield of 2.91 g/L in shake-flask fermentation, which was elevated by 66.3 % compared to that of the parent strain FEEL-1. Subsequent batch and fed-batch fermentation was performed in a 5 L fermenter, and 8.2 g/L and 41.2 g/L ε-PL productions were achieved, which were 49.1 % and 68.1 % higher, respectively, than those of the parent strain. Analysis of enzyme activities indicated that key enzymes, e.g., hexokinase, pyruvate kinase, citrate synthase and aspartate kinase, were more active in the mutant AS3-14 than in FEEL-1, which might explain the enhanced ε-PL productivity. The results of amplified fragment length polymorphism analysis indicated that the genomic DNA of AS3-14 became more variable after ARTP mutagenesis. Therefore, ARTP combined with streptomycin resistance is an efficient breeding approach for the rapid evolution of ε-PL-producing Streptomyces strains.

A limited number of antifungal drugs, the side-effect of clinical drugs and the emergence of resistance create an urgent need for new antifungal treatment agents. High-throughput drug screening and in-depth drug action mechanism analyzation are needed to address this problem. In this study, we identified that artemisinin and its derivatives possessed antifungal activity through a high-throughput screening of the FDA-approved drug library. Subsequently, drug-resistant strains construction, a molecular dynamics simulation and a transcription level analysis were used to investigate artemisinin’s action mechanism in Candida glabrata. Transcription factor pleiotropic drug resistance 1 (PDR1) was an important determinant of artemisinin’s sensitivity by regulating the drug efflux pump and ergosterol biosynthesis pathway, leading to mitochondrial dysfunction. This dysfunction was shown by a depolarization of the mitochondrial membrane potential, an enhancement of the mitochondrial membrane viscosity and an upregulation of the intracellular ROS level in fungi. The discovery shed new light on the development of antifungal agents and understanding artemisinin’s action mechanism.

This work identified the role of microbial elicitors on ε-PL production and disclosed the underlying mechanism through analysis of gene transcription, key enzyme activities, and intracellular metabolite pools, including transcriptome and metabolome analysis. It was the first report for the inducing effects of the “microbial call” to Streptomyces albulus and ε-PL biosynthesis, and these elicitors could be potentially obtained from decayed fruits infected by Botrytis cinerea ; hence, this may be a way of turning a biohazard into bioproduct wealth.