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Avilamycin, an excellent growth-promoting feed additive, produced by Streptomyces viridochromogenes, was widely used to promote the growth of poultry by inhibiting Gram-positive bacteria. In this work, the methods of combinational mutagenesis of UV (Ultraviolet) and ARTP (Atmospheric and room temperature plasma), and rational screening by high concentrations of CaCl 2 were utilized to promote the production of avilamycin. The avilamycin high-yielding mutant strains of Z-6 (29.31 mg/L), A-9 (36.84 mg/L) and F-23 (45.73 mg/L) were screened out, with yields of avilamycin improved by 57.92%, 98.49% and 146.39%, respectively, compared with the wild strain (WT). The performance comparison showed that Z-6, A-9 and F-23 mutant strains had stronger abilities of substrate consumption, cell growth and antibiotic synthesis than WT. Furthermore, the composition of fermentation medium, inoculation parameters, supplementation strategies of oxygen vectors, glucose and precursors (L-valine, D-xylose and sodium acetate) had been optimized and the avilamycin yield of the mutant strain F-23 was significantly enhanced by 41.87% by fermentation optimization. In summary, the strategy of increasing the production of avilamycin in S. viridochromogenes in this work might provide an alternative method to enhance the synthesis of secondary metabolites in other Streptomyces., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

ε-poly-l-lysine (ε-PL) has been routinely used as a natural and safe preservative for many years in the food industry. However, most existing production methods struggle to achieve low cost and high production simultaneously. In this work, we present a co-culture fermentation strategy to enhance ε-PL production. Specifically, we screened a strain from five different strains that could be co-cultured with Streptomyces albulus to raise the production of ε-PL. Subsequently, a single factor experiment and response surface design were used to optimize the conditions of co-culture fermentation to further improve the production of ε-PL. Moreover, the optimal fermentation process was successfully verified in a 2-L fermentor with fed batch fermentation. The production of ε-PL reached 27.07 ± 0.47 g/L by 144 h. Compared with single strain (S. albulus) fermentation, the production of ε-PL was increased by 31.47%. At the same time, the amount of bacteria increased by 19.62%, which means that the ε-PL synthesis ability of bacteria had been improved. All the obtained results showed great potential for co-culture fermentation in large-scale ε-PL production and provide a new fermentation strategy for ε-PL biosynthesis. [ABSTRACT FROM AUTHOR]