Differences in Acid Stress Response of Lacticaseibacillus paracasei Zhang Cultured from Solid-State Fermentation and Liquid-State Fermentation

The investigation of the mechanism underlying variations in oxidative stress tolerance of Lacticaseibacillus paracasei resulting from fermentation methods through endogenous CRISPR-Cas9 editing methodology

The probiotic effects of lactic acid bacteria make them widely used in human and animal breeding industry. However, the presence of oxidative stress during the production and application process can cause bacterial damage or even death, significantly compromising the functionality of probiotics. Despite its potential for broader application scenarios that could provide a more comprehensive understanding of bacteria's internal adaptation strategies, there is a lack of research investigating oxidative stress from the perspective of culture methods. In this study, the tolerance to oxidative stress was compared between bacteria cultivated through solid-state fermentation (SSF) and liquid-state fermentation (LSF), and the physiological and transcriptional disparities between these two bacterial strains were investigated. Additionally, a novel and efficient gene editing method was developed to elucidate the genetic basis underlying these differences in tolerance. The results demonstrated a significantly higher tolerance to oxidative stress in SSF bacteria compared to LSF bacteria, along with a stronger capacity for maintaining intracellular microenvironment stability and the activity of key metabolic enzymes. It is noteworthy that the bacteria from SSF significantly enhance the transport of carbohydrate substances and facilitate intracellular metabolic flow. Gene editing experiments have confirmed the crucial role of genes glpF and glpO in regulating the glycerol metabolism pathway, which is essential for enhancing the tolerance of bacteria from SSF to oxidative stress. Based on these findings, the mechanism underlying the disparity in oxidative stress tolerance resulting from different culture methods has been summarized. Furthermore, investigation into different culture modes has revealed that moderate oxygen levels during cultivation significantly influence variation in bacterial tolerance to oxidative stress. Importantly, these variations are species-specific and depend on the ecological niche distribution of Lactobacilli. These findings elucidate a novel mechanism by which Lacticaseibacillus paracasei Zhang tolerates oxidative stress, and also suggest that distinct cultivation and processing methods should be tailored based on the specific Lactobacilli groups to achieve optimal application effects in production.

Revisiting fermented buckwheat: a comprehensive examination of strains, bioactivities, and applications

Buckwheat, a nutrient-rich pseudocereal, is known for its various biological properties, but its antinutritional factors, such as phytic acid and tannins, can hinder nutrient absorption. Fermentation improves buckwheat's nutritional profile by enhancing bioactive compounds, increasing digestibility, and reducing antinutritional factors. This review comprehensively examines the effects of fermentation and microbial strains on the nutritional composition and functional properties of buckwheat, highlighting their impact on health benefits and potential applications in diverse food products. Fermentation significantly boosts essential nutrients, including amino acids, vitamins, minerals, and bioactive compounds, while reducing antinutritional factors like phytic acid and protease inhibitors. It also enhances antioxidant, antidiabetic, hypolipidemic, anti-inflammatory, and gut microbiota-regulating properties. However, there are notable gaps in research, including limited understanding of fermentation process control, heavy metal transformation, and pathogenic microorganism effects during fermentation. Addressing these gaps is crucial for optimizing the functional properties and ensuring the safety of fermented buckwheat in the food industry. Overall, fermented buckwheat holds significant potential as a functional ingredient for gluten-free foods, nondairy beverages, and other health-promoting products that cater to specific dietary needs.

Genomic and Metabolomic Analyses of Streptomyces albulus with Enhanced ε-Poly-l-lysine Production Through Adaptive Laboratory Evolution

ε-poly-l-lysine (ε-PL), a natural food preservative, has garnered widespread attention. It is mainly produced by Streptomyces albulus, but the production by wild-type strains fails to meet the demands of industrialization. To address this issue, adaptive laboratory evolution (ALE) was successfully employed in this study, subjecting S. albulus CICC 11022 to environmental stresses such as acidic pH and antibiotics (rifampicin, gentamicin, and streptomycin). As a result of ALE, an evolutionary strain S. albulus C214 was obtained, exhibiting an increase in ε-PL production and cell growth by 153.23% and 234.51%, respectively, as compared with the original strain. Genomic and metabolic analyses revealed that mutations occurred in genes responsible for transcriptional regulation, transporter, cell envelope, energy metabolism, and secondary metabolite synthesis, as well as the enrichment of metabolites involved in the biosynthesis of ε-PL. These findings hold great significance for elucidating the mechanism underlying ε-PL synthesis.

Mechanisms of thermal, acid, desiccation and osmotic tolerance of Cronobacter spp

Cronobacter spp. exhibit remarkable resilience to extreme environmental stresses, including thermal, acidic, desiccation, and osmotic conditions, posing significant challenges to food safety. Their thermotolerance relies on heat shock proteins (HSPs), thermotolerance genomic islands, enhanced DNA repair mechanisms, and metabolic adjustments, ensuring survival under high-temperature conditions. Acid tolerance is achieved through internal pH regulation, acid efflux pumps, and acid tolerance proteins, allowing survival in acidic food matrices and the gastrointestinal tract. Desiccation tolerance is mediated by the accumulation of protective osmolytes like trehalose, stabilizing proteins and membranes to withstand dryness, especially in dry food products. Similarly, osmotic stress resilience is supported by compatible solutes such as trehalose and glycine betaine, along with metabolic adaptations to balance osmotic pressures. These mechanisms highlight the adaptability of Cronobacter spp. to diverse environments. Moreover, exposure to sublethal stresses, including heat, osmotic, dry, and pH stresses, may induce homologous or cross-resistance, complicating control strategies. Understanding these survival mechanisms is essential to mitigate the risks of Cronobacter spp., especially in powdered infant formula (PIF), and ensure food safety.