Fermented foods are important parts of traditional food culture with a long history worldwide. Abundant nutritional materials and open fermentation contribute to the diversity of microorganisms, resulting in unique product quality and flavor. Lactic acid bacteria (LAB), as important part of traditional fermented foods, play a decisive role in the quality and safety of fermented foods. Reproduction and metabolic of microorganisms drive the food fermentation, and microbial interaction plays a major role in the fermentation process. Nowadays, LAB have attracted considerable interest due to their potentialities to add functional properties to certain foods or as supplements along with the research of gut microbiome. This review focuses on the characteristics of diversity and variability of LAB in traditional fermented foods, and describes the principal mechanisms involved in the flavor formation dominated by LAB. Moreover, microbial interactions and their mechanisms in fermented foods are presented. They provide a theoretical basis for exploiting LAB in fermented foods and improving the quality of traditional fermented foods. The traditional fermented food industry should face the challenge of equipment automation, green manufacturing, and quality control and safety in the production. Graphical Abstract

The pursuit of obtaining enzymes with high activity and stability remains a grail in enzyme evolution due to the stability-activity trade-off. Here, we develop an isothermal compressibility-assisted dynamic squeezing index perturbation engineering (iCASE) strategy to construct hierarchical modular networks for enzymes of varying complexity. Molecular mechanism analysis elucidates that the peak of adaptive evolution is reached through a structural response mechanism among variants. Furthermore, this dynamic response predictive model using structure-based supervised machine learning is established to predict enzyme function and fitness, demonstrating robust performance across different datasets and reliable prediction for epistasis. The universality of the iCASE strategy is validated by four sorts of enzymes with different structures and catalytic types. This machine learning-based iCASE strategy provides guidance for future research on the fitness evolution of enzymes.

The polyethylene terephthalate hydrolase (PETase) has been proved to have a high activity to degrade polyethylene terephthalate(PET), but few studies has been carried on its secretion in Bacillus subtilis. In this study, the coding gene of PETase, which was isolated from the Ideonella sakaiensis, was synthesized and expressed in B. subtilis. Then we evaluated the ability of five Bacillus signal peptides to enhance PETase secretion by B. subtilis. The results indicated that the SP_amy‐induced secretion of PETase was the highest, and its activity against p‐Nitrophenyl palmitate was about fourfold that of the natural signal peptide SP_PETase. The weak promoter P43 provided sufficient time for translation and folding of PETase, resulting in increased extracellular expression. Use of P43 and SP_amy in combination yielded the greatest bis‐(2‐hydroxyethyl) terephthalate degradation and PET‐film etching activity due to maximized secretion of PETase by B. subtilis. Our findings will facilitate biodegradation of PET plastic.