The flexible linker and CotG were more effective for the spore surface display of keratinase KERQ7

Surface Display Technologies for Whole-Cell Biocatalysts: Advances in Optimization Strategies, Food Applications, and Future Perspectives

Surface display technology has revolutionized whole-cell biocatalysis by enabling efficient enzyme immobilization on microbial cell surfaces. Compared with traditional enzyme immobilization, this technology has the advantages of high enzyme activity, mild process, simple operation and low cost, which thus has been widely studied and applied in various fields. This review explores the principles, optimization strategies, applications in the food industry, and future prospects. We summarize the membrane and anchor protein structures of common host cells (Escherichia coli, Bacillus subtilis, and yeast) and discuss cutting-edge optimization approaches, including host strain genetic engineering, rational design of anchor proteins, innovative linker peptide engineering, and precise regulation of signal peptides and promoters, to maximize surface display efficiency. Additionally, we also explore its diverse applications in food processing and manufacturing, additive synthesis, food safety, and other food-related industries (such as animal feed and PET packaging degradation), demonstrating their potential to address key challenges in the food industry. This work bridges fundamental research and industrial applications, offering valuable insights for advancing agricultural and food chemistry.

Exploring the potential of spore surface-displayed keratinase for feather waste degradation using high-throughput screening

BACKGROUND

With the development of the global poultry industry, millions of tons of feathers are produced each year. A significant proportion is improperly discarded, leading to a substantial loss of keratin resources from feathers. Utilizing feathers in the feed industry could reduce costs substantially. However, the new fermented feed industry lacks acid-resistant keratinase, making it unable to convert feather keratin effectively in a lactic acid bacteria fermentation environment.

RESULTS

This study established a high-throughput screening method using spore surface-display to identify acid-resistant mutants generated by error-prone PCR. A mutant H4 (N43K/N143I) was obtained with a significant increase in activity under acidic conditions, and it was 1.34-fold more active than the wild type in a pH 5 environment. Bioinformatic analysis showed that the increase in stress resistance and activity of H4 was due to an increase in certain weak interaction forces and alterations in energy levels. The addition of H4 spore suspension as an enzyme preparation to feather meal fermentation feed with the participation of lactic acid bacteria improved the content of small peptides and free amino acids significantly. After being subjected to short-term high-temperature treatments, the H4 spore preparation was still able to degrade chicken feathers.

CONCLUSION

These results suggest that the spore surface-displayed keratinase mutant H4 has potential for improved effectiveness in feather degradation within the fermented feed industry. © 2025 Society of Chemical Industry.

Three-step surface design of spore-displayed keratinase improved acid tolerance and feather degradation

The global chicken business has grown rapidly, producing millions of tons of feather waste annually. Keratinase is a special enzyme that catalyzes the degradation of keratin and can be applied to the feed industry. In this study, we initially set the tone for the acid-resistant mutation of spore surface-display keratinase cotG-KERQ7 by replacing base-catalytic residues in the active center. We then performed molecular dynamics simulations of the KERQ7-AAPF, the enzyme-substrate complex, to enhance both acid stability and activity by substituting unstable positively charged amino acids on the surface. Finally, based on the change of protein rigidity-flexibility, a flexible tentacle outside the catalytic pocket was introduced to enhance the feather meal degradation activity of KERQ7 in an acidic environment. The Ding-F was finally obtained through the three-step design of keratinase surface. The mutant Ding-F was able to break down feather meal better in both lactobacillus-fermented feed environments and simulated gastric fluid digestion environments. This study not only establishes a theoretical foundation for the development of keratinases used in lactobacillus-fermented feed, but it also generates a three-step surface design method that can serve as a guide for future general strategies aimed at modifying the acid resistance of serine keratinases.

Perspective on Agricultural Industrialization: Modification Strategies for Enhancing the Catalytic Capacity of Keratinase

Keratinases is a special hydrolytic enzyme produced by microorganisms, which has the ability to catalyze the degradation of keratin. Currently, keratinases show great potential for application in many agricultural and industrial fields, such as biofermented feed, leather tanning, hair removal, and fertilizer production. However, these potentials have not yet been fully unleashed on an industrial scale. This paper reviews the sources, properties, and catalytic mechanisms of keratinases. Strategies for the molecular modification of keratinases are summarized and discussed in terms of improving the substrate specificity, thermostability, and pH tolerance of keratinases. The modification strategies are also enriched by the introduction of immobilized enzymes and directed evolution. In addition, the selection of modification strategies when facing specific industrial applications is discussed and prospects are provided. We believe that this review serves as a reference for the future quest to extend the application of keratinases from the laboratory to industry.

Surface display system of Bacillus subtilis: A promising approach for improving the stability and applications of cellobiose dehydrogenase

Cellobiose dehydrogenase (CDH) plays a crucial role in lignocellulose degradation and bioelectrochemical industries, making it highly in demand. However, the production and purification of CDH through fungal heterologous expression methods is time-consuming, costly, and challenging. In this study, we successfully displayed Pycnoporus sanguineus CDH (psCDH) on the surface of Bacillus subtilis spores for the first time. Enzymatic characterization revealed that spore surface display enhanced the tolerance of psCDH to high temperature (80 °C) and low pH levels (3.5) compared to free psCDH. Furthermore, we found that glycerol, lactic acid, and malic acid promoted the activity of immobilized spore-displayed psCDH; glycerol has a more significant stimulating effect, increasing the activity from 16.86 ± 1.27 U/mL to 46.26 ± 3.25 U/mL. After four reuse cycles, the psCDH immobilized with spores retained 48% of its initial activity, demonstrating a substantial recovery rate. In conclusion, the spore display system, relying on cotG, enables the expression and immobilization of CDH while enhancing its resistance to adverse conditions. This system demonstrates efficient enzyme recovery and reuse. This approach provides a novel method and strategy for the immobilization and stability enhancement of CDH.