Physiological, Morphological and Antioxidant Responses of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 Isolated from Harbin Dry Sausages to Oxidative Stress

Active induction: a promising strategy for enhancing the bioactivity of lactic acid bacteria

Lactic acid bacteria (LAB), as key probiotic, play crucial roles in maintaining human health. However, their survival and functionality in diverse habitats depend on their ability to sense and respond to environmental stresses. Notably, active induction has emerged as a promising strategy for regulating the biological activity of LAB, potentially enhancing their health benefits. Therefore, this review summarizes the beneficial effects of active induction, including acid, bile, oxidation, ethanol, heat, cold, and radiation induction on the functional activities of LAB. In addition, omics methods, in silico analysis, and gene editing technologies have greatly facilitated the profound exploration of the stress regulatory network in LAB, thereby aiding the identification of active components and stress adaptors. Through these advancements, LAB provide health benefits by regulating stress-related genes and proteins, as well as inducing bioactive metabolite production. As a result, they could enhance stress tolerance, cross-protection, intestinal colonization, adhesion properties, and provide antialcohol and liver protection in vitro or in vivo. This study highlights the potential of active induction strategies in enhancing the functional role of LAB in food applications.

Computational Analysis of Morphological Changes in Lactiplantibacillus plantarum Under Acidic Stress

Shape and size often define the characteristics of individual microorganisms. Hence, characterizing cell morphology using computational image analysis can aid in the accurate, quick, unbiased, and reliable identification of bacterial morphology. Modifications in the cell morphology of Lactiplantibacillus plantarum were determined in response to acidic stress, during the growth stage of the cells at a pH 3.5 compared to a pH of 6.5. Consequently, we developed a computational method to sort, detect, analyze, and measure bacterial size in a single-species culture. We applied a deep learning methodology composed of object detection followed by image classification to measure bacterial cell dimensions. The results of our computational analysis showed a significant change in cell morphology in response to alterations of the environmental pH. Specifically, we found that the bacteria existed as a long unseparated cell, with a dramatic increase in length of 41% at a low pH compared to the control. Bacterial width was not altered in the low pH compared to the control. Those changes could be attributed to modifications in membrane properties, such as increased cell membrane fluidity in acidic pH. The integration of deep learning and object detection techniques, with microbial microscopic imaging, is an advanced methodology for studying cellular structures that can be projected for use in other bacterial species or cells. These trained models and scripts can be applied to other microbes and cells.

Enhancing the application of probiotics in probiotic food products from the perspective of improving stress resistance by regulating cell physiological function: A review

Probiotic foods are foods containing probiotics, including dairy and non-dairy products, that exert significant beneficial impacts on human health. Benefiting from the rapid progress in systems biology, diverse types of probiotics with prominent health-promoting functionalities are unraveled, albeit such functions could be substantially influenced by the stress environments. Here, we conducted a comprehensive review to characterize the state-of-the-art research on probiotic foods and specific probiotics employed in their production. We summarized the detrimental effects of various environmental stresses, including those encountered during industrial fermentation and storage (in vitro), as well as in vivo conditions such as digestion and intestinal colonization, on the biological functions of probiotics. Furthermore, this review outlines the recent advancements in elucidating the mechanisms of stress resistance, which are expected to enhance targeted probiotic applications and optimize their functional properties. Additionally, we summarized various strategies aimed at improving stress tolerance by regulating cell physiological function, specifically adaptive laboratory evolution, preadaptation treatment, exogenous supplementation, and molecular biological manipulation. This review underscores the significance of enhancing our understanding of stress tolerance mechanisms at a systems level and developing efficacious anti-stress strategies to enhance the application of probiotics while maximizing their biological functionalities.

Deciphering styrene oxide tolerance mechanisms in Gluconobacter oxydans mutant strain

Chemical production wastewater contains large amounts of organic solvents (OSs), which pose a significant threat to the environment. In this study, a 10 g·L-1 styrene oxide tolerant strain with broad-spectrum OSs tolerance was obtained via adaptive laboratory evolution. The mechanisms underlying the high OS tolerance of tolerant strain were investigated by integrating physiological, multi-omics, and genetic engineering analyses. Physiological changes are one of the main factors responsible for the high OS tolerance in mutant strains. Moreover, the P-type ATPase GOX_RS04415 and the LysR family transcriptional regulator GOX_RS04700 were also verified as critical genes for styrene oxide tolerance. The tolerance mechanisms of OSs can be used in biocatalytic chassis cell factories to synthesize compounds and degrade environmental pollutants. This study provides new insights into the mechanisms underlying the toxicological response to OS stress and offers potential targets for enhancing the solvent tolerance of G. oxydans.

Adaptive Laboratory Evolution of Probiotics toward Oxidative Stress Using a Microfluidic-Based Platform

Adaptive laboratory evolution (ALE) can be used to make bacteria less susceptible to oxidative stress. An alternative to large batch scale ALE cultures is to use microfluidic platforms, which are often more economical and more efficient. Microfluidic ALE platforms have shown promise, but many have suffered from subpar cell passaging mechanisms and poor spatial definition. A new approach is presented using a microfluidic Evolution on a Chip (EVoc) design which progressively drives microbial cells from areas of lower H2O2 concentration to areas of higher concentration. Prolonged exposure, up to 72 h, revealed the survival of adaptive strains of Lacticaseibacillus rhamnosus GG, a beneficial probiotic often included in food products. After performing ALE on this microfluidic platform, the bacteria persisted under high H2O2 concentrations in repeated trials. After two progressive exposures, the ability of L. rhamnosus to grow in the presence of H2O2 increased from 1 mm H2O2 after a lag time of 31 h to 1 mm after 21 h, 2 mm after 28 h, and 3 mm after 42 h. The adaptive strains have different morphology, and gene expression compared to wild type, and genome sequencing revealed a potentially meaningful single nucleotide mutation in the protein omega-amidase.

The Changes Occurring in Proteins during Processing and Storage of Fermented Meat Products and Their Regulation by Lactic Acid Bacteria

Protein, which is the main component of meat, is degraded and oxidized during meat fermentation. During fermentation, macromolecular proteins are degraded into small peptides and free amino acids, and oxidation leads to amino acid side chain modification, molecular crosslinking polymerization, and peptide chain cleavage. At different metabolic levels, these reactions may affect the protein structure and the color, tenderness, flavor, and edible value of fermented meat products. Lactic acid bacteria are currently a research hotspot for application in the fermented meat industry. Its growth metabolism and derivative metabolites formed during the fermentation of meat products regulate protein degradation and oxidation to a certain extent and improve product quality. Therefore, this paper mainly reviews the changes occurring in proteins in fermented meat products and their effects on the quality of the products. Referring to studies on the effects of lactic acid bacteria on protein degradation and oxidation from all over the world, this review aims to provide a relevant reference for improving the quality of fermented meat products.

Adaptive Response of Thermophiles to Redox Stress and Their Role in the Process of dye Degradation From Textile Industry Wastewater

Release of dye-containing textile wastewater into the environment causes severe pollution with serious consequences on aquatic life. Bioremediation of dyes using thermophilic microorganisms has recently attracted attention over conventional treatment techniques. Thermophiles have the natural ability to survive under extreme environmental conditions, including high dye concentration, because they possess stress response adaptation and regulation mechanisms. Therefore, dye detoxification by thermophiles could offer enormous opportunities for bioremediation at elevated temperatures. In addition, the processes of degradation generate reactive oxygen species (ROS) and subject cells to oxidative stress. However, thermophiles exhibit better adaptation to resist the effects of oxidative stress. Some of the major adaptation mechanisms of thermophiles include macromolecule repair system; enzymes such as superoxide dismutase, catalase, and glutathione peroxidase; and non-enzymatic antioxidants like extracellular polymeric substance (EPSs), polyhydroxyalkanoates (PHAs), etc. In addition, different bacteria also possess enzymes that are directly involved in dye degradation such as azoreductase, laccase, and peroxidase. Therefore, through these processes, dyes are first degraded into smaller intermediate products finally releasing products that are non-toxic or of low toxicity. In this review, we discuss the sources of oxidative stress in thermophiles, the adaptive response of thermophiles to redox stress and their roles in dye removal, and the regulation and crosstalk between responses to oxidative stress.

Assessment of Ultrasonic Stress on Survival and β-Glucosidase Activity of Encapsulated Lactiplantibacillus plantarum BCRC 10357 in Fermentation of Black Soymilk

The enhanced β-glucosidase activity of encapsulated Lactiplantibacillus plantarum BCRC 10357 within calcium alginate capsules was investigated by ultrasonic stimulation to induce the stress response of the bacteria for the biotransformation of isoflavones in black soymilk. The effects of various ultrasound durations, sodium alginate concentrations (% ALG), and cell suspensions on the β-glucosidase activity of encapsulated bacteria were explored. The β-glucosidase activity of encapsulated L. plantarum BCRC 10357 with ultrasonic stimulation (40 kHz/300 W) was greater than that without ultrasound. With 20 min of ultrasonic treatment, the β-glucosidase activity of encapsulated L. plantarum BCRC 10357 from 2% ALG/0.85% NaCl cell suspension was 11.47 U/mL at 12 h, then increased to 27.43 U/mL at 36 h and to 26.25 U/mL at 48 h in black soymilk at 37 °C, showing the high adaptation of encapsulated L. plantarum BCRC 10357 encountering ultrasonic stress to release high β-glucosidase until 48 h, at which point the ratio of isoflavone aglycones (daidzein and genistein) in total isoflavones (daidzin, genistin, daidzein, and genistein) was 98.65%, reflecting the effective biotransformation of isoflavone glycosides into aglycones by β-glucosidase. In this study, the survivability and β-glucosidase activity of encapsulated L. plantarum BCRC 10357 were enhanced under ultrasonic stimulation, and were favorably used in the fermentation of black soymilk.

Probiotic Effects and Metabolic Products of Enterococcus faecalis LD33 with Respiration Capacity

Respiration metabolism could improve the long-term survival of lactic acid bacteria (LAB); however, its effect on potential probiotic traits of LAB was not reported. The difference made by Enterococcus faecalis LD33 that was cultured under respiration-permissive and fermentation conditions, such as the biomass, metabolites, antimicrobial activity, tolerance to acid and bile salt, adhesion capabilities, and the ability to inhibit the proliferation of cancer cells were studied. Under a respiration-permissive condition, the final biomass of the culture was about twice as compared to that of fermentation condition. When the metabolites were measured, glucose was exhausted within 8 h. Two-folds of acetic acid, triple of both acetoin and diacetyl, and less than half of lactic acid, were accumulated under the respiratory-permissive condition. No discrimination of growth inhibition on Salmonella enterica serovar Typhimurium ATCC 14028 and Shigella sonnei ATCC 25931 was observed when Enterococcus faecalis LD33 was cultured under both conditions; however, under respiration-permissive condition, the strain presented significant antimicrobial activities to Listeria monocytogenes ATCC19111 and Staphylococcus aureus ATCC6538P. Enterococcus faecalis LD33 displayed relatively strong bile salt tolerance and adherence capability but weaker acid tolerance when undergoing respiration metabolism. There was no significant difference in the anti-cancer effect of the viable bacterial cells on both growth modes; however, the supernatant showed a higher inhibition effect on HT-29 cells than the live bacteria, and there was no significant difference between the supernatant and the 5-Fluorouracil (7 μg/mL). Consequently, the Enterococcus faecalis LD33 undergoing respiration metabolism could bring higher biomass, more flavor metabolites, and better antimicrobial and anti-cancer activities. This study extends our knowledge of respiratory metabolism in LAB and its impact on probiotic traits. E. faecalis LD33 qualifies as a suitable strain against foodborne pathogens, cancer therapy, and eventual application in the food and pharmaceutical industries.

Fortified Fermented Rice-Acid Can Regulate the Gut Microbiota in Mice and Improve the Antioxidant Capacity

The study aimed to explore the effects of fortified fermented rice-acid on the antioxidant capacity of mouse serum and the gut microbiota. Hair characteristics, body mass index, intestinal villus height, intestinal crypt depth, serum antioxidant capacity, and gut microbiota of mice were first measured and the correlation between the antioxidant capacity of mouse serum and the gut microbiota was then explored. The mice in the lactic acid bacteria group (L-group), the mixed bacteria group (LY-group), and the rice soup group (R-group) kept their weight well and had better digestion. The mice in the L-group had the better hair quality (dense), but the hair quality in the R-group and the yeast group (Y-group) was relatively poor (sparse). In addition, the inoculation of Lactobacillus paracasei H4-11 (L. paracasei H4-11) and Kluyveromyces marxianus L1-1 (K. marxianus L1-1) increased the villus height/crypt depth of the mice (3.043 ± 0.406) compared to the non-inoculation group (R-group) (2.258 ± 0.248). The inoculation of L. paracasei H4-11 and K. marxianus L1-1 in fermented rice-acid enhanced the blood antioxidant capacity of mouse serum (glutathione 29.503 ± 6.604 umol/L, malonaldehyde 0.687 ± 0.125 mmol/L, catalase 15.644 ± 4.618 U/mL, superoxide dismutase 2.292 ± 0.201 U/mL). In the gut microbiota of L-group and LY-group, beneficial microorganisms (Lactobacillus and Blautia) increased, but harmful microorganisms (Candidatus Arthromitus and Erysipelotrichales) decreased. L. paracasei H4-11 and K. marxianus L1-1 might have a certain synergistic effect on the improvement in antibacterial function since they reduced harmful microorganisms in the gut microbiota of mice. The study provides the basis for the development of fortified fermented rice-acid products for regulating the gut microbiota and improving the antioxidant capacity.