[Metabolic engineering of Streptomyces for production of hyaluronic acid]

Hyaluronic acid (HA) is a glycosaminoglycan with significant biological activities, which render it widely applicable in the cosmetics and pharmaceutical industries. The development of safe and efficient chassis cells to enhance HA synthesis efficiency has thus emerged as a key factor in HA production. Our study aims to construct a high-performance HA biosynthesis system using Streptomyces as the chassis cell, thereby providing technical support for the efficient microbial production of HA. Thus, our study focused on the metabolic engineering of Streptomyces for strengthening the HA synthesis pathway and then optimized the culture conditions for efficient HA synthesis. First, the HA-synthesizing capabilities of four hyaluronate synthases from different sources were evaluated in two host strains: Streptomyces coelicolor M1146 and Streptomyces albus J1074. The results indicated that the hyaluronate synthases derived from Streptococcus pyogenes exhibited the strongest HA synthesis capability. Notably, the HA yield in S. albus J1074 was higher. Building on this finding, S. albus J1074 was selected as the starting strain to construct a chassis strain tailored for HA synthesis: key genes in the competitive metabolic pathway of HA synthesis were knocked out, while the expression levels of genes associated with the bypass pathway were down-regulated. Furthermore, different combinations of key genes involved in the HA precursor synthesis pathway were designed, and their expression levels were enhanced via a constitutive strong promoter. The recombinant strain obtained therefrom achieved a maximum HA yield of 2.62 g/L. Finally, the synthetic capacity of this high-yield engineered strain was further unleased through the optimization of culture conditions, leading to a final HA yield of 4.63 g/L. The recombinant strain constructed in this study not only lays a foundation for the development of engineered Streptomyces but also provides an excellent chassis strain for the microbial production of HA and other related bioproducts.