Facile and green synthesis of reduced graphene oxide/loofah sponge for Streptomyces albulus immobilization and ε-poly-l-lysine production

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.

Design and optimization of ε-poly-l-lysine with specific functions for diverse applications

ε-Poly-l-lysine (ε-PL) is a natural homo-poly(amino acid) which can be produced by microorganisms. With the advantages in broad-spectrum antimicrobial activity, biodegradability, and biocompatibility, ε-PL has been widely used as a preservative in the food industry. Different molecular architectures endow ε-PL and ε-PL-based materials with versatile applications. However, the microbial synthesis of ε-PL is currently limited by low efficiencies in genetic engineering and molecular architecture modification. This review presents recent advances in ε-PL production and molecular architecture modification of microbial ε-PL, with a focus on the current challenges and solutions for the improvement of the productivity and diversity of ε-PL. In addition, we highlight recent examples where ε-PL has been applied to expand the versability of edible films and nanoparticles in various applications. Commercial production and the challenges and future research directions in ε-PL biosynthesis are also discussed. Currently, although the main use of ε-PL is as a food preservative, ε-PL and ε-PL-based polymers have shown excellent application potential in biomedical fields. With the development of synthetic biology, the design and synthesis of ε-PL with a customized molecular architecture are possible in the near future. ε-PL-based polymers with specific functions will be a new trend in biopolymer manufacturing.

Recovery of methane and acetate during ex-situ biogas upgrading via novel dual-membrane aerated biofilm reactor

Biological biogas upgrading has been well-proven to be a promising approach for renewable bioenergy recovery, but hydrogen (H₂)-assisted ex-situ biogas upgrading is hindered by a large solubility discrepancy between H₂ and carbon dioxide (CO₂). This study established a new dual-membrane aerated biofilm reactor (dMBfR) to improve the upgrading efficiency. Results showed that dMBfR operated at 1.25 atm H₂ partial pressure, 1.5 atm biogas partial pressure, and 1.0 d hydraulic retention time could significantly improve the efficiency. The maximum methane purity of 97.6%, acetate production rate of 34.5 mmol L^-1d^-1, and H₂ and CO₂ utilization ratios of 96.5% and 96.3% were achieved. Further analysis showed that the improved performances of biogas upgrading and acetate recovery were positively correlated with the total abundances of functional microorganisms. Taken together, these results suggest that the dMBfR, which facilitates the precise CO₂ and H₂ supply, is an ideal approach for efficient biological biogas upgrading.

Metatranscriptome Revealed the Efficacy and Safety of a Prospective Approach for Agricultural Wastewater Reuse: Achieving Ammonia Retention during Biological Treatment by a Novel Natural Inhibitor Epsilon-Poly-l-Lysine

Appropriate inhibitors might play important roles in achieving ammonia retention in biological wastewater treatment and its reuse in agriculture. In this study, the feasibility of epsilon-poly-l-lysine (ε-PL) as a novel natural ammonia oxidation inhibitor was investigated. Significant inhibition (ammonia oxidation inhibition rate was up to 96.83%) was achieved by treating the sludge with ε-PL (400 mg/L, 12 h soaking) only once and maintaining for six cycles. Meanwhile, the organic matter and nitrite removal was not affected. This method was effective under the common environmental conditions of biological wastewater treatment. Metatranscriptome uncovered the possible action mechanisms of ε-PL. The ammonia oxidation inhibition was due to the co-decrease of Nitrosomonas abundance, ammonia oxidation genes, and the cellular responses of Nitrosomonas. Thauera and Dechloromonas could adapt to ε-PL by stimulating stress responses, which maintained the organic matter and nitrite removal. Importantly, ε-PL did not cause the enhancement of antibiotic resistance genes and virulent factors. Therefore, ε-PL showed a great potential of ammonia retention, which could be applied in the biological treatment of wastewater for agricultural reuse.