Bioconversion of agricultural waste to ε-poly-L-lysine by an engineered Streptomyces albulus strain.

The vast majority of agricultural wastes are burned or buried in soil currently, causing environmental pollution and resource waste worldwide. To achieve the eco-friendly bioconversion of agricultural waste, this study utilized an engineered Streptomyces albulus for solid-state fermentation (SSF) to convert rapeseed cake into ε-poly-L-lysine (ε-PL), the L-lysine homopolymer widely applied as a natural and safe food preservative. Firstly, based on genome analysis and the property characterization of agricultural waste, the bioconversion potential of S. albulus toward lignocellulosic waste was revealed, followed by preliminary experimental validation. Secondly, the high-titer engineered strain was obtained by overexpressing key genes eno1, eno2, pepc, ask and pls of ε-PL biosynthesis pathway, thereby promoting the bioconversion of rapeseed cake. Among the mutants, S. albulus PLS got the highest ε-PL titer, which was 9.3-fold that of the control strain in SSF. And the ε-PL titer was further increased to 1.6 times the original via optimizing SSF process. Finally, we characterized the growth and development status and the lignocellulose biodegradation of S. albulus PLS during the bioconversion process. Overall, this study identified a strategy for the valorization of agricultural waste, and the engineered strain offers a promising SSF microbial chassis for ε-PL production from lignocellulosic waste.