Biofilms enhance microbial tolerance to harsh environments while preserving cellular activity over prolonged periods. Although biofilm-based continuous fermentation is widely applied for production of small-molecule chemicals, its application to macromolecular protein production has been rarely reported. Here, FimH, an adhesin from E. coli fimbriae that is employed for mannose-specific adherence and promotes biofilm formation, was displayed on the surface of S. cerevisiae using the anchoring proteins Sag1C, Sed1, Cwp2 and Ccw12, resulting in an 80–150 % enhancement in biofilm formation. Among them, Sed1 was the most effective, followed by Sag1C. A biofilm-based fermentation system for continuous secretion of human lysozyme (hLYZ) was established via cell-surface display of FimH in S. cerevisiae, achieving stable operation for over 350 h. The engineered strain BY4742-Sag1C-hlyz achieved an average extracellular hLYZ activity of 113.1 U/mL, significantly higher than the control BY4742-hlyz (41.6 U/mL), owing to enhanced cell adhesion that increased the total cell number in biofilm-based fermentation. Its productivity reached 2.36 U/mL/h, representing a 77.4 % increase compared with free-cell fermentation of BY4742-hlyz (1.33 U/mL/h). In conclusion, this study first achieved heterologous expression of a bacterial biofilm-forming gene in S. cerevisiae, enhancing biofilm formation and providing a reference for future expression of bacterial biofilm-related genes in yeast. Furthermore, biofilm-based fermentation enabled continuous secretion of hLYZ, highlighting a promising strategy for continuous production of recombinant proteins.

Background: Over the past 40 years since the discovery of regenerating family proteins (Reg proteins), numerous studies have highlighted their biological functions in promoting cell proliferation and resisting cell apoptosis, particularly in the regeneration and repair of pancreatic islets and exocrine glands. Successively, short peptides derived from Reg3δ and Reg3α have been employed in clinical trials, showing favorable therapeutic effects in patients with type I and type II diabetes. However, continued reports have been limited, presumably attributed to the potential side effects. Methods: This review summarizes extensive research on Reg proteins over the past decade, combined with our own related studies, proposing that Reg proteins exhibit dimorphic effects. Results: The activity of Reg proteins is not as simplistic as previously perceived but shows auto-immunogenicity depending on different pathophysiological microenvironments. The immunogenicity of Reg proteins could recruit immune cells leading to an anti-tumor effect. Such functional diversity is correlated with their structural characteristics: the N-terminal region contributes to autoantigenicity, while the C-type lectin fragment near the C-terminal determines the trophic action. It should be noted that B-cell masking antigens might also reside within the C-type lectin domain. Conclusions: Reg proteins have dual functional roles under various physiological and pathological conditions. These theoretical foundations facilitate the subsequent development of diagnostic reagents and therapeutic drugs targeting Reg proteins.