Combinatorial strain improvement and bioprocess development for efficient production of ε-poly-L-lysine in Streptomyces albulus.

ε-Poly-L-lysine (ε-PL) is an amino acid homopolymer with diverse potential applications in the food, pharmaceutical and cosmetic industries. To improve its biomanufacturing efficiency, strain engineering and bioprocess optimization were combined in this study. Firstly, a cocktail strain breeding strategy was employed to generate a ε-PL high-production mutant, Streptomyces albulus GS114, with enhanced L-lysine uptake capability. Subsequently, the L-lysine feeding conditions during fed-batch fermentation were systematically optimized to improve the L-lysine supply, resulting in ε-PL production reaching 73.1 ± 1.4 g/L in 5 L bioreactor. Finally, an engineered strain, S. albulus L2, with enhanced uptake capability and polymerization ability of L-lysine was constructed, achieving ε-PL production of 81.4 ± 5.2 g/L by fed-batch fermentation. This represents the highest reported production of ε-PL to date. This study provided an efficient production strategy for ε-PL and valuable insights into the high-value utilization of L-lysine.

[Breeding and fermentation performance of a high-yield ε-poly-Llysine producing strain].

Objective: A high yield of ε-poly-L-lysine (ε-PL) producing strain was bred, and the effect of different carbon sources on fermentation performance was studied. Methods: Genome shuffling and ribosome engineering were used to enhanced strain's productivity, and pH shock strategy was used to fermentation using different carbon sources. Results: After four rounds of genome shuffling and ribosome engineering, we obtained a high yield mutant Streptomyces albulus GS114 with ε-PL productivity of 3.0 g/L, which was 1.7 folds than that of the initial strain. When we performed fed-batch fermentation using glucose and glycerol as carbon sources in a 5-L fermenter, ε-PL productions reached 43.4 and 45.7 g/L after 192 h fed-batch fermentations, which were increased by 11.0% and 14.9% than that of Streptomyces albulus M-Z18, respectively. Meanwhile, the dry cell weights decreased by 24.0% and 33.2%, and ε-PL yields increased by 34.2% and 30.7%, respectively. Conclusion: Genome shuffling and ribosome engineering are effective to breed high yield strains.

[Enhanced ε-poly-L-lysine production through pH regulation and organic nitrogen addition in fed-batch fermentation].

During the production of ε-poly-L-lysine (ε-PL) in fed-batch fermentation, the decline of ε-PL synthesis often occurs at middle or late phase of the fermentation. To solve the problem, we adopted two strategies, namely pH shift and feeding yeast extract, to improve the productivity of ε-PL. ε-PL productivity in fermentation by pH shift and feeding yeast extract achieved 4.62 g/(L x d) and 5.16 g/(L x d), which were increased by 27.3% and 42.2% compared with the control ε-PL fed-batch fermentation, respectively. Meanwhile, ε-PL production enhanced 36.95 g/L and 41.32 g/L in 192 h with these two strategies, increased by 27.4% and 42.48% compared to the control, respectively. ε-PL production could be improved at middle or late phase of fed-batch fermentation by pH shift or feeding yeast extract.