Lactobacillus, Bifidobacterium and Lactococcus response to environmental stress: Mechanisms and application of cross-protection to improve resistance against freeze-drying

Impact of Freezing and Freeze Drying on Lactobacillus rhamnosus GG Survival: Mechanisms of Cell Damage and the Role of Pre-Freezing Conditions and Cryoprotectants

Lactobacillus rhamnosus GG (LGG) is a common lactic acid bacteria used in the food industry with proven health benefits. Maintaining a high viability of probiotics during freeze drying and storage is crucial for their efficacy. The involvement of protectants and the optimization of operating conditions are promising techniques utilized to help bacteria microorganisms overcome environmental challenges. Although numerous studies have investigated the effectiveness of various protective agents in mitigating environmental stresses on bacterial cells and improving their survival during freeze drying, there is limited understanding of how freezing parameters impact the process by influencing ice crystal formation and bacterial cell microstructure. Therefore, this study systematically evaluates the effects of freeze-thawing and freeze-drying processes on the survival and metabolic activity of LGG. The results reveal that cell damage during freezing and freeze drying is a complex process influenced by a variety of physicochemical factors, including freezing conditions, sublimation and thawing processes, as well as the choice of cryoprotectants and reconstitution medium. Notably, freezing with water in liquid nitrogen at -196 °C resulted in the highest bacterial survival rate (90.94%) under short freezing durations, demonstrating the importance of freezing conditions. Freeze drying further reduced viability, with survival rates dropping to as low as 2% under suboptimal conditions. Interestingly, phosphate-buffered saline as a resuspension medium significantly increased the loss of viable LGG during both freezing and freeze drying. The addition of trehalose and skim milk as cryoprotectants enhanced survival to 15.17% post-freeze drying, emphasizing the role of protective agents in improving viability. This study provides novel insights into the critical role of freezing parameters and operational conditions in preserving probiotic viability, offering valuable guidelines for optimizing the freeze-drying process to maintain the functionality of probiotics.

Proteomic Analysis of Bifidobacterium animalis AR668 and AR668-R1 Under Aerobic Culture

Bifidobacterium animalis is a widely used probiotic with significant health benefits, but its application is limited by oxygen sensitivity. Our laboratory previously developed an oxygen-tolerant B. animalis AR668-R1 using adaptive laboratory evolution under aerobic culture, but the molecular mechanism remains unclear. In this work, compared to the wild-type parental strain B. animalis AR668, 212 upregulated and 390 downregulated proteins were identified in AR668-R1 under aerobic conditions through comparative proteomic analysis. Enrichment analysis of the differentially expressed proteins between AR668 and AR668-R1 identified the potential oxygen-tolerant related pathways, including the translation process, transmembrane transport system, and carbohydrate metabolism. Furthermore, five potential oxygen-tolerance proteins (DapE, Mth2, MutT, Eno, and MsrAB) were validated by RT-qPCR that may contribute to the aerobic growth of AR668-R1. Through gene overexpression validation, Mth2 (7,8-dihydro-8-oxoguanine triphosphatase) was found to enhance the growth of AR668-R1 by 19.8% compared to the empty plasmid control under aerobic conditions. Our finding provides valuable insights into the oxygen-tolerant mechanisms of B. animalis at the protein level.

Nutrient consumption patterns of Streptococcus thermophilus F7 under acid stress and their application in enhancing biomass production

The nutrient consumption patterns of Streptococcus thermophilus F7 under acid stress were investigated in this study. The strain was incubated at 42°C for 16 h in a chemically defined medium with different pH values (6.5, 5.8, and 5.5), and consumption of a variety of nutrients including amino acids, vitamins, purine/pyrimidine bases, and ions was observed. The results showed that Leu was the most consumed amino acid at all pH levels, and the consumption values were 2.5, 3.4, and 4.5 μmol/cfu × 10-5 at pH 6.5, 5.8, and 5.5, respectively. Consumption of biotin was the highest among vitamins, ranging from 48.3 nmol/cfu × 10-5 at pH 6.5 to 126.7 nmol/cfu × 10-5 at pH 5.5. At pH 6.5, adenine was the most consumed purine (78.3 nmol/cfu × 10-5), whereas uracil became the most consumed base under more acid stress, with values of 122.5 and 122.2 nmol/cfu × 10-5 at pH 5.8 and 5.5, respectively. Regarding ion consumption, Na+ was predominant at pH 6.5 (35.4 μmol/cfu × 10-5) and 5.8 (41.0 μmol/cfu × 10-5), whereas K+ was the most consumed ion when pH dropping to 5.5 (61.9 μmol/cfu × 10-5). Certain highly demanded nutrients were individually added to the medium under the same incubation conditions, and the results revealed that at pH 5.8, the optical density at 600 nm of S. thermophilus F7 supplemented with 1.5 times or 2 times of isoleucine increased by 1.13 folds compared with the initial medium. Similarly, at pH 5.5, supplementation with 3 times of proline or adenine resulted in a 1.15-fold or 1.12-fold increase in optical density at 600 nm, respectively. This study showed significant differences in the consumption of various nutrients when culturing S. thermophilus F7, which had the highest requirement for amino acids, followed by ions, vitamins, and pyrimidine bases. Furthermore, the individual addition of amino acids and pyrimidine bases showed improvement in biomass production of the strain. The findings of the present study provide a basis on the nutrient requirements of S. thermophilus F7 and contribute to the design of media for high-cell-density cultivation.

Evaluation of probiotic properties and complete genome analysis of lactic acid bacteria isolated from crested ibis Nipponia nippon feces

Introduction

Crested ibis (Nipponia nippon) is a rare bird whose intestinal tract is rich in lactic acid bacteria (LAB), but there is less research on LAB isolated from crested ibises.

Methods

From the fecal samples, Twenty isolates were obtained from fecal samples and subjected to a series of tests, including biochemical identification, acid and bile tolerance assays, in vitro pathogen inhibition, cell surface hydrophobicity assessment, antibiotic susceptibility testing, and hemolytic activity evaluation to determine their probiotic potential. We fed L. plantarum E7 to mice to evaluate safety. Nanopore PromethION48 and the Illumina Novaseq sequencing platforms were used to sequence the genome of L. plantarum E7.

Results

Five isolates (D1, D2, D6, E7 and D8) were able to survive under low acid and high bile salt conditions. Except for D8, the other four isolates (D1, D2, D6 and E7) exhibited inhibitory activity against tested pathogens. Strain E7 displayed the least resistance to antibiotics, and only E7 showed medium hydrophobicity. Further characterization identified strain E7 as Lactiplantibacillus plantarum (L. plantarum) through 16S rDNA sequencing. We did not observe adverse effects of L. plantarum E7 on growth performance, blood cell composition in mice. L. plantarum E7 consists of a circular chromosome and two circular plasmids. The chromosome encodes 3024 genes that associated with cell adhesion, acid and bile salt tolerance, antioxidant enzymes, as well as the production of secondary metabolites. In contrast, the plasmids contain fewer coding genes. Functional annotation via KEGG and GO database analysis indicated that the genes of L. plantarum E7 are primarily involved in carbohydrate metabolism, amino acid metabolism, vitamin and cofactor metabolism, biological process, and molecular function.

Conclusion

This study provides a theoretical foundation for developing new probiotic for crested ibises.

New insights into the cultivability of human milk bacteria from ingestion to digestion and implications for their Immunomodulatory properties

Human milk (HM) microbiota is increasingly studied for its potential health benefits. However, the physiological state of HM bacteria and consequently their effects on gut homeostasis remain a question. This study investigated the physiological state of the HM microbiota by characterizing its cultivable fraction as it might be at the point of ingestion and assessing the effects of digestion, in the specific context of the immature infant digestive tract, on the cultivability and immunomodulatory properties of six HM strains representative of prevalent genera in HM. Twenty-eight HM samples were analysed by 16 S metabarcoding either directly on raw milk (raw milk microbiota, RM) or on the complete cultivable fraction obtained from seven non-selective media (cultivable milk microbiota, CM). This approach enabled a more in-depth investigation of CM than conventional methods based on the individual sequencing of a subset of isolates and resulted in a moderate gain in diversity within each HM sample. It confirmed that diversity was lower in CM than in RM, with ~ 7 versus 69 genera per sample in CM and RM respectively, and an under-representation of strictly anaerobic genera in CM. In vitro infant gastrointestinal digestion resulted in overall good survival of the 6 HM strains but partial or complete loss of their immunomodulatory properties on the monocyte THP1 cell line, except for a Staphylococcus epidermidis strain that gained immunomodulatory potential. These results highlight the potential of HM bacteria to survive during the infant gastrointestinal digestion and interact with the intestinal epithelium and immune system, as well as the importance of considering the digestion process when evaluating host-bacteria interactions.

Methionine affects the freeze-drying resistance of Lactiplantibacillus plantarum LIP-1 by improving its antioxidant capacity

BACKGROUND

Lactic acid bacteria is an essential industrial strain, and improving its freeze-drying survival rate is the key challenge to ensuring the activity and stability of bacterial powder. Although medium optimization has been shown to strengthen strain freeze-drying tolerance, the mechanism by which amino acids repair freeze-drying damage in lactic acid bacteria remains unclear. This study investigated the effects of methionine on the freeze-drying survival rate of Lactiplantibacillus plantarum LIP-1 and explored the underlying protective mechanisms.

RESULTS

The study demonstrates that supplementing the medium with 0.06 g/L methionine significantly improved the freeze-drying survival rate of Lactiplantibacillus plantarum LIP-1 (P < 0.05). Further analysis revealed that the strain significantly reduced intracellular reactive oxygen species levels through metabolizing methionine (P < 0.05), decreased the oxidation degree of unsaturated fatty acids in the cell membrane, and reduced cell membrane damage, thereby strengthening the freeze-drying resistance of the strain.

CONCLUSION

Methionine can enhance the freeze-drying resistance of Lactiplantibacillus plantarum LIP-1 by enhancing antioxidant capacity and maintaining the stability of the subcellular structure. This study provides a specific reference value for improving the freeze-drying survival rate of lactic acid bacteria by modifying the medium conditions. © 2025 Society of Chemical Industry.

Functional diversity of AI-2/LuxS system in lactic acid bacteria: Impacts on biofilm formation and environmental resilience

A key component of microbial communication, autoinducer-2 (AI-2) signaling, affects several physiological processes, including environmental adaptation and biofilm formation in lactic acid bacteria (LAB). The multifarious contribution of AI-2, synthesized by LuxS, in improving biofilms and tolerance to hostile conditions in LAB has been investigated in this review. The evolutionary conservation and diversity of AI-2 are shown by a phylogenetic analysis of luxS gene among several LAB species. Furthermore, AI-2 signaling in LAB improves resistance to unfavorable environmental factors, including pH fluctuations, temperature extremes, and antimicrobial agents. Lactic acid bacteria could set off defenses against harmful impacts from environmental stresses.

Overview of Glycometabolism of Lactic Acid Bacteria During Freeze-Drying: Changes, Influencing Factors, and Application Strategies

Lactic acid bacteria (LAB) play a vital role in food fermentation and probiotics microeconomics. Freeze-drying (FD) is a commonly used method for preserving LAB powder to extend its shelf life. However, FD induces thermal, osmotic, and mechanical stresses that can impact the glycometabolism of LAB, which is the process of converting carbohydrates into energy. This review explores the effect of FD on glycometabolism, factors influencing glycometabolism, and feasible strategies in the FD process of LAB. During the three stages of FD, freezing, primary drying or sublimation, and second drying, the glycolytic activity of LAB is disrupted in the freezing stage; further, the function of glycolytic enzymes such as hexokinase, phosphofructokinase, and pyruvate kinase is hindered, and adenosine triphosphate (ATP) production drops significantly in the sublimation stage; these enzyme activities and ATP production nearly cease and exopolysaccharide (EPS) synthesis alters during the secondary drying stage. Factors such as strain variations, pretreatment techniques, growth medium components, FD parameters, and water activity influence these changes. To counteract the effects of FD on LAB glycometabolism, strategies like cryoprotectants, encapsulation, and genetic engineering can help preserve their glycometabolic activity. These methods protect LAB from harsh FD conditions, safeguarding glycolytic flux and enzymatic processes involved in carbohydrate metabolism. A deeper understanding of these glycometabolic changes is essential for optimizing FD processes and enhancing the use of LAB in food, medicine, and biotechnology, ultimately improving their performance upon rehydration.

A Closer Look at the Potential Mechanisms of Action of Protective Agents Used in the Drying of Microorganisms: A Review

Yeast, bacteria and sourdough are widely used in our daily lives, yet their drying and storage remains a significant challenge. A variety of techniques are used to improve the resistance of cells to thermal, dehydration, oxidative and osmotic stresses, which can occur at different stages of the process. The addition of protective agents prior to drying is a commonly used method, but the mechanisms that may lead to a change in viability following the addition of these agents, or more generally, the interaction between a protective agent and the drying process, are not yet fully understood. This review outlines seven main potential mechanisms, as highlighted in the literature, which can lead to internal or external modifications of the cells. The mechanisms in question are change of membrane fluidity, accumulation of compounds for osmoregulation, prior osmotic dehydration, prevention of oxidation, coating or encapsulation, enhancement in thermal resistance and change in drying kinetics. A comprehensive explanation of these mechanisms is provided. This review also highlights the connection between the mechanisms and the influence of the stresses occurring during drying and storage, which depend on the drying technique used and the operating conditions, the strains and the protective agents involved, on the importance of the different protection mechanisms. By gaining a deeper understanding of the mechanisms of action of protective agents, strategies to improve the quality of the microorganisms obtained after drying can be developed. One such strategy would be to combine several agents to achieve a synergistic effect.

Recent Advances in the Understanding of Stress Resistance Mechanisms in Probiotics: Relevance for the Design of Functional Food Systems

In recent years, more and more scientific community, food producers, and food industry show increased interest in functional foods containing probiotics, which is a big challenge. The consumption of probiotics in the context of a balanced diet through the consumption of functional foods or through the intake of pharmaceutical preparations has proven to contribute to the improvement of human health, even contributing to the prevention of diseases. In order for probiotics to be considered suitable for consumption, they must contain a minimum concentration of viable cells, namely, at least 107 colony forming units of beneficial microbes per gram. Ensuring the viability of bacterial cells until the moment of consumption is the overriding priority of functional probiotic food manufacturers. Probiotic bacteria are subject to stress conditions not only during food manufacturing but also during gastrointestinal passage, which limit or even compromise their functionality. This paper first examines all the stressful conditions faced by probiotic cells in their production stages and related to the conditions present in the bioreactor fermentation and drying processes as well as factors related to the food matrix and storage. The stress situations faced by probiotic microorganisms during the gastrointestinal transit especially during stomach and intestinal residence are also analyzed. In order to understand the adaptation mechanisms of probiotic bacteria to gastrointestinal stress, intrinsic and adaptive mechanisms identified in probiotic strains in response to acid stress and to bile and bile acid stress are analyzed. In addition, improvement strategies for multiple stress tolerance of lactic acid bacteria through directions dealing with stress, accumulation of metabolites, use of protectants, and regulation of technological parameters are examined. Finally, the definition of postbiotics, inanimate microorganisms and/or their components conferring health benefits, is also introduced. Postbiotics include cell lysates, enzymes, and cell wall fragments derived from probiotic bacteria and may represent an alternative to the use of probiotics, when they do not tolerate stressful conditions.

Orange Peel Lactiplantibacillus plantarum: Development of A Mucoadhesive Nasal Spray with Antimicrobial and Anti-inflammatory Activity

Background/Objectives: Due to the high frequency and severity of upper respiratory bacterial infections, probiotics could offer a new medical approach. We explored the antibacterial and anti-inflammatory properties of the new strain Lactiplantibacillus plantarum BIA and formulated a nasal spray. Methods:L. plantarum BIA was isolated from orange peel and taxonomically identified through 16S rRNA gene sequencing. Its antibacterial activity was tested against Pseudomonas aeruginosa, Streptococcus pyogenes, Bacillus subtilis, Escherichia coli, and Staphylococcus aureus, while anti-inflammatory potential was evaluated by Griess assay. BIA genome was fully sequenced and analyzed to assess its safety. BIA was formulated in a freeze-dried matrix, containing prebiotics and cryoprotectants, to be reconstituted with a polymer solution. Solutions containing two types of hydroxypropyl methylcellulose (HPMC) and hyaluronic acid were evaluated as resuspending media and compared in terms of pH, viscosity, and mucoadhesion ability. The biological activity of BIA formulated as nasal spray was verified together with the stability of the selected formulations. Results:L. plantarum BIA inhibited human pathogens' growth and showed anti-inflammatory activity and a safe profile. In the best-performing formulation, the probiotic is lyophilized in 10% fructooligosaccharides, 0.1% ascorbic acid, and 0.5% lactose and reconstituted with HPMC high viscosity 1% w/v. This composition ensured the probiotic's viability for up to six months in its dried form and one week after reconstitution. It also allowed interaction with the nasal mucosa, preserving its antimicrobial and anti-inflammatory activities. Conclusion: The developed nasal spray could become a promising formulation in the field of nasal infectious and inflammatory diseases.

What We Know About the Actual Role of Traditional Probiotics in Health and Disease

The complex relationship between probiotics and human health goes beyond their traditional function in gut health, generating considerable interest for their broad potential in disease treatment. This review explores the various functions of probiotics, highlighting their impact on the immune system, their benefits for gut and oral health, their effects on metabolic and neurological disorders, and their emerging potential in cancer therapy. We give significant importance to studying the effects of probiotics on the gut-brain axis, revealing new and non-invasive therapeutic approaches for complex neurological disorders. In addition, we expand the discussion to encompass the impact of probiotics on the gut-liver and gut-lung axes, recognizing their systemic effects and potential in treating respiratory and hepatic conditions. The use of probiotic "cocktails" to improve cancer immunotherapy outcomes indicates a revolutionary approach to oncological treatments. The review explores the specific benefits associated with various strains and the genetic mechanisms that underlie them. This study sets the stage for precision medicine, where probiotic treatments can be tailored to meet the unique needs of each patient. Recent developments in delivery technologies, including microencapsulation and nanotechnology, hold great potential for enhancing the effectiveness and accuracy of probiotic applications in therapeutic settings. This study provides a strong basis for future scientific research and clinical use, promoting the incorporation of probiotics into treatment plans for a wide range of diseases. This expands our understanding of the potential benefits of probiotics in modern medicine.

A protective mechanism of heat inactivation to enhance Levilactobacillus brevis PDD-2 against alcohol-induced chronic liver disease based on proteomic analysis

A proteomics-based analysis of the effect of heat inactivation on the alleviation of alcoholic liver disease (ALD) using Levilactobacillus brevis PDD-2 is presented, aimed at exploring the potential and mechanisms of postbiotic elements prepared through heat inactivation in the treatment of ALD. It was found that L. brevis PDD-2 and its postbiotic (heat-inactivated L. brevis PDD-2) alleviate chronic ALD via the gut-liver axis. In particular, heat-inactivated L. brevis PDD-2 significantly increased the relative abundance of Erysipelotrichaceae and better facilitated the oxidative stress balance in the liver. The tandem mass tag (TMT)-based quantitative proteomics technique analyses revealed that heat-inactivated L. brevis PDD-2 was associated with up-regulated expression levels of proteins related to the redox system, cellular metabolism, amino acid and oligopeptide transport, and surface proteins with immunomodulatory capacity. These findings provide a theoretical basis for developing novel therapeutic strategies and lay a solid foundation for further revealing its exhaustive mechanisms.

Acid tolerance responses and their mechanisms in Lactiplantibacillus plantarum LM1001

This study investigated the acid tolerance responses of Lactiplantibacillus plantarum LM1001 at physiological and molecular levels. Upon exposure to low pH, L. plantarum LM1001 demonstrated increased ATPase activity and ammonia consumption, which contributed to a higher intracellular pH. Comparative analysis of cell membrane fatty acids revealed that acid-stressed cells had a significantly higher proportion of unsaturated fatty acids than those of unstressed cells. There was differential upregulation of several genes, notably those involved in alkali production (arcB, argG, and argH) and in class I and class III stress responses (clpE, clpP, hrcA, dnaK, grpE, groEL, and groES). Following 2-h exposure to pH 2.5, L. plantarum LM1001 not only exhibited enhanced survival but also showed increased auto-aggregation and improved mucin adhesion capability, albeit with a reduction in hydrophobicity. These findings indicate that acid stress induces adaptive physiological and metabolic changes in L. plantarum LM1001, enhancing its acid resistance and adherence properties.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-024-01582-4.

Lactobacillus Persisters Formation and Resuscitation

Lactobacillus is a commonly used probiotic, and many researchers have focused on its stress response to improve its functionality and survival. However, studies on persister cells, dormant cells that aid bacteria in surviving general stress, have focused on pathogenic bacteria that cause infection, not Lactobacillus. Thus, understanding Lactobacillus persister cells will provide essential clues for understanding how Lactobacillus survives and maintains its function under various environmental conditions. We treated Lactobacillus strains with various antibiotics to determine the conditions required for persister formation using kill curves and transmission electron microscopy. In addition, we observed the resuscitation patterns of persister cells using single-cell analysis. Our results show that Lactobacillus creates a small population of persister cells (0.0001-1% of the bacterial population) in response to beta-lactam antibiotics such as ampicillin and amoxicillin. Moreover, only around 0.5-1% of persister cells are heterogeneously resuscitated by adding fresh media; the characteristics are typical of persister cells. This study provides a method for forming and verifying the persistence of Lactobacillus and demonstrates that antibiotic-induced Lactobacillus persister cells show characteristics of dormancy, sensitivity of antibiotics, same as exponential cells, multi-drug tolerance, and resuscitation, which are characteristics of general persister cells. This study suggests that the mechanisms of formation and resuscitation may vary depending on the characteristics, such as the membrane structure of the bacterial species.

Fermentation properties and functional stability of dough starter Jiaozi and Laomian after frozen storage

Purpose

This study aims to investigate the effects of frozen storage on the stability of traditional dough starters in China.

Methods

The microbial community structure and abundance of related metabolic genes in different fermented sourdough prepared by Jiaozi (JZ) and Laomian (LM) starters before and after frozen storage at -20°C for half a year were analyzed using the shotgun metagenomic sequencing method, and differences in characteristics of texture in steamed bread were also compared by formal methods.

Results

The fermentation ability (FA) and metabolic activities of yeast in the JZH sourdough (started by JZ which was stored at -20°C for half a year) were better than those of LMH sourdough (started by LM which was stored at -20°C for half a year). The dominant genera of Acetobacter were found to be increased in the JZH0 sourdough (started by JZH and fermented for 0 h) and those of Lactobacillus were found to be decreased. Lactobacillus (98.72%), Pediococcus (0.37%), Saccharomyces (0.27%), and Acetobacter (0.01%), were dominant in sourdough LMH0 (started by LMH and fermented for 0 h). The abundances of "oxidative phosphorylation-related enzymes" and the "biosynthesis of glutamate"-related enzymes and genes related to "biosynthesis of glutamate" and "unsaturated fatty acid" were higher in JZH0 than in the JZ0 sourdough (started by JZ without being frozen and fermented for 0 h). The good FA of yeast, the acid production capacity of bacteria in the sourdough, and the quality of the JZH steamed bread (made by the JZH starter) indicated the better freezing tolerance of the microorganisms in JZ than in LM.

Conclusion

The conclusion of this study suggests the better application potential of the JZ as the fermentation starter in actual production.

Unraveling the Genetic Adaptations in Cell Surface Composition and Transporters of Lactiplantibacillus plantarum for Enhanced Acid Tolerance

This study employed adaptive laboratory evolution to improve the acid tolerance of Lactiplantibacillus plantarum, a vital strain in food fermentation and a potential probiotic. Phenotype and genomic analyses identified the overexpression of stress response proteins, ATP synthases, and transporters as pivotal in conferring acid tolerance to the evolved strains. These adaptations led to a shorter lag phase, improved survival rates, and higher intracellular pH values compared to the wild-type strain under acid stress conditions. Additionally, the evolved strains showed an increased expression of genes in the fatty acid synthesis pathway, resulting in a higher production of unsaturated fatty acids. The changes in cell membrane composition possibly prevented H+ influx, while mutant genes related to cell surface structure contributed to observed elongated cells and thicker cell surface. These alterations in cell wall and membrane composition, along with improved transporter efficiency, were key factors contributing to the enhanced acid tolerance in the evolved strains.

Strategies to enhance stress tolerance in lactic acid bacteria across diverse stress conditions

Lactic acid bacteria (LAB) hold significant importance in diverse fields, including food technology, industrial biotechnology, and medicine. As basic components of starter cultures, probiotics, immunomodulators, and live vaccines, LAB cells resist a variety of stressors, including temperature fluctuations, osmotic and pH shocks, exposure to oxidants and ultraviolet radiation, substrate deprivation, mechanical damage, and more. To stay alive in these adversities, LAB employ a wide range of stress response strategies supported by various mechanisms, for example rearrangement of metabolism, expression of specialized biomolecules (e.g., chaperones and antioxidants), exopolysaccharide synthesis, and complex repair and regulatory systems. LAB can coordinate responses to various stressors using global regulators. In this review, we summarize current knowledge about stress response strategies used by LAB and consider mechanisms of response to specific stressful factors, supported by illustrative examples. In addition, we discuss technical approaches to increase the stress resistance of LAB, including pre-adaptation, genetic modification of strains, and adjustment of cultivation conditions. A critical analysis of the recent findings in this field augments comprehension of stress tolerance mechanisms in LAB, paving the way for prospective research directions with implications in fundamental and practical areas.

Extremophiles: the species that evolve and survive under hostile conditions

Extremophiles possess unique cellular and molecular mechanisms to assist, tolerate, and sustain their lives in extreme habitats. These habitats are dominated by one or more extreme physical or chemical parameters that shape existing microbial communities and their cellular and genomic features. The diversity of extremophiles reflects a long list of adaptations over millions of years. Growing research on extremophiles has considerably uncovered and increased our understanding of life and its limits on our planet. Many extremophiles have been greatly explored for their application in various industrial processes. In this review, we focused on the characteristics that microorganisms have acquired to optimally thrive in extreme environments. We have discussed cellular and molecular mechanisms involved in stability at respective extreme conditions like thermophiles, psychrophiles, acidophiles, barophiles, etc., which highlight evolutionary aspects and the significance of extremophiles for the benefit of mankind.

In-silico functional analysis of hypothetical proteins from Lactiplantibacillus plantarum plasmids reveals enrichment of cell envelope proteins

Lactiplantibacillus plantarum is one of the important species of lactic acid bacterium (LAB) found in diverse environments, with many strains exhibiting probiotic properties. In our previous study, 41.6% of protein families (PFs) encoded by 395 plasmids from several L. plantarum strains were found to be hypothetical proteins with no predicted function. This study aimed at predicting the functions of these 647 hypothetical proteins using 21 different bioinformatics methods. As a result, 160 PFs could be newly annotated. A lower proportion of plasmid-specific functions was annotated as compared to the functions shared between plasmids and chromosomes. Also, hypothetical proteins were less conserved than the annotated proteins across L.plantarum plasmids. Based on the subcellular localization, cell envelope proteins represented the biggest category in the newly annotated proteins. Transporters (112 PFs) which was a part of cell envelop proteins represented the largest functional group. Additionally, 40 and 25 other PFs were predicted to contain signal peptides and transmembrane helices, respectively. We speculate that such hypothetical proteins might be involved in the transport of various chemicals and environmental interactions in L. plantarum. In the future, functional characterization of these proteins through wet-lab experimental approach can provide novel insights into their contribution to the physiology, probiotic properties, and industrial utility of these bacteria.

Whole genome sequence analysis enabled affirmation of the probiotic potential of marine sporulater Bacillus amyloliquefaciens BTSS3 isolated from Centroscyllium fabricii

Probiotics are microorganisms when administered in adequate amounts, confer health benefits on the host. Many probiotics find application in various industries however, probiotic bacteria linked to marine environments are less explored.Although Bifidobacteria, Lactobacilli, and Streptococcus thermophilus are the most frequently used probiotics, Bacillus spp. have acquired much acceptance in human functional foods due to their increased tolerance and enduring competence in harsh environments like the gastrointestinal (GI) tract. In this study, the 4 Mbp genome sequence of Bacillus amyloliquefaciens strain BTSS3, a marine spore former isolated from deep-sea shark Centroscyllium fabricii, with antimicrobial and probiotic properties was sequenced, assembled, and annotated. Analysis revealed the presence of numerous genes presenting probiotic traits like production of vitamins, secondary metabolites, amino acids, secretory proteins, enzymes and other proteins that allow survival in GI tract as well as adhesion to intestinal mucosa. Adhesion by colonization in the gut was studied in vivo in zebrafish (Danio rerio) using FITC labelled B.amyloliquefaciens BTSS3. Preliminary study revealed the ability of the marine Bacillus to attach to the intestinal mucosa of the fish gut. The genomic data and the in vivo experiment affirms that this marine spore former is a promising probiotic candidate with potential biotechnological applications.

Effects of sublethal stress application on the survival of bacterial inoculants: a systematic review

The use of commercial bacterial inoculants formulated with plant-growth promoting bacteria (PGPB) in agriculture has shown significant prominence in recent years due to growth-promotion benefits provided to plants through different mechanisms. However, the survival and viability of bacterial cells in inoculants are affected during use and may decrease their effectiveness. Physiological adaptation strategies have attracted attention to solve the viability problem. This review aims to provide an overview of research on selecting sublethal stress strategies to increase the effectiveness of bacterial inoculants. The searches were performed in November 2021 using Web of Science, Scopus, PubMed, and Proquest databases. The keywords "nitrogen-fixing bacteria", "plant growth-promoting rhizobacteria", "azospirillum", "pseudomonas", "rhizobium", "stress pre-conditioning", "adaptation", "metabolic physiological adaptation", "cellular adaptation", "increasing survival", "protective agent" and "protective strategy" were used in the searches. A total of 2573 publications were found, and 34 studies were selected for a deeper study of the subject. Based on the studies analysis, gaps and potential applications related to sublethal stress were identified. The most used strategies included osmotic, thermal, oxidative, and nutritional stress, and the primary cell response mechanism to stress was the accumulation of osmolytes, phytohormones, and exopolysaccharides (EPS). Under sublethal stress, the inoculant survival showed positive increments after lyophilization, desiccation, and long-term storage processes. The effectiveness of inoculant-plants interaction also had positive increments after sublethal stress, improving plant development, disease control, and tolerance to environmental stresses compared to unappealed inoculants.

Changes in nutrient consumption patterns of Lactobacillus fermentum mediated by sodium lactate

BACKGROUND

During high-cell-density culture of Lactobacillus fermentum, the optimal pH is often maintained by adding NaOH. During cultivation at controlled pH, L. fermentum experiences osmotic stress due to the continuous accumulation of sodium lactate as a neutralizer product, affecting its survival in subsequent processing. The purpose of this study was to evaluate the nutrient consumption patterns of L. fermentum ATCC 14931 under sodium lactate stress and to screen nutrients that help it resist osmotic stress.

RESULTS

The consumption and consumption rates of amino acids, purines, pyrimidines, vitamins, and metal ions were analyzed in chemically defined media containing 0.13, 0.31, or 0.62 mm L^-1 sodium lactate. The highest consumption rates were found for arginine, guanine, folic acid, and Mn²⁺ , and the most consumed nutrients were glutamate + glutamine, guanine, ascorbic acid, and Na⁺ . Arginine 2.58 mm L^-1 , guanine 0.23 mm L^-1 , and Mn²⁺ 0.25 mm L^-1 were added to the medium at sodium lactate concentrations of 0.13 and 0.62 mm L^-1 , and arginine 2.58 mm L^-1 , guanine 0.26 mm L^-1 , and Mn²⁺ 0.25 mm L^-1 at a sodium lactate concentration of 0.31 mm L^-1 . The viable cell counts of L. fermentum ATCC 14931 were approximately 1.02-fold (P < 0.05) of the counts observed in control medium at all three concentrations of sodium lactate.

CONCLUSION

The present results suggest that certain nutrients accelerate the growth of L. fermentum under sodium lactate stress and enhance its resistance to this adverse condition. © 2022 Society of Chemical Industry.

Preparation and Application of Directed Vat Set Indigenous Freeze-Drying Lentilactobacillus hilgardii Q19 Starter in Winemaking

In order to prepare a better direct vat set for malolactic fermentation (MLF) in high ethanol and low pH wines, the high-ethanol- and low-temperature-tolerant strain Lentilactobacillus hilgardii Q19, which was isolated from the eastern foothill of the Helan Mountain wine region in China, was used to prepare a direct vat set by vacuum freeze-drying. A superior freeze-dried lyoprotectant was obtained to create the starting culture by selecting, combining, and optimizing numerous lyoprotectants with higher protection for Q19 by using a single-factor experiment and response surface approach. Finally, the Lentilactobacillus hilgardii Q19 direct vat set was inoculated in Cabernet Sauvignon wine to carry out MLF on a pilot scale, with commercial starter culture Oeno1 as control. The volatile compounds, biogenic amines, and ethyl carbamate content were analyzed. The results showed that a combination of 8.5 g/100 mL skimmed milk powder, 14.5 g/100 mL yeast extract powder, and 6.0 g/100 mL sodium hydrogen glutamate offered better protection; with this lyoprotectant, there were (4.36 ± 0.34) × 10¹¹ CFU/g cells after freeze-drying, and it showed an excellent ability to degrade L-malic acid and could successfully finish MLF. In addition, in terms of aroma and wine safety, compared with Oeno1, the quantity and complexity of volatile compounds were increased after MLF, and biogenic amines and ethyl carbamate were produced less during MLF. We conclude that the Lentilactobacillus hilgardii Q19 direct vat set could be applied as a new MLF starter culture in high-ethanol wines.

Effects of anaerobic and respiratory adaptation of Lacticaseibacillus casei N87 on fermented sausages production

Lacticaseibacillus casei N87 was used as starter culture for the production of fermented sausages. The strain was cultivated in anaerobic (A) and respiratory (growth in presence of oxygen and supplementation with haeme and menaquinone in the growth medium; R) conditions. Control without the starter culture inoculation and with the addition of 150 mg/kg of nitrate was also included. The effect on physico-chemical parameters (pH, Aw, weight loss, and color), microbial population, volatilome, proteolysis as well as the survival of the strain was evaluated during 90 days of ripening. Q-PCR and DGGE-PCR analyses demonstrated the ability of the strain used in this study to adapt to this environment and carry out the sausage's fermentation process. The inoculation of the strain did not have any effect on the Aw values, which decreased similarly in the different samples whereas the pH was lower in A samples (5.2) and the weight loss in R samples (2.5% less than the others). The color parameters of the samples inoculated with the starter cultures were comparable to those of the control added with nitrate. The concentration of aldehydes that usually are identified as marker of oxidation processes was similar in the samples inoculated with the starter cultures adapted under respiratory conditions and in the control. On the contrary, a higher level was detected in the samples inoculated with the starter cultivated under anaerobic conditions. The proteolysis that occurred during the ripening indicates the differentiation of the A samples from the others. Nonetheless, the volatile profiles of the inoculated fermented sausages were similar. The study demonstrated that aerobic adaptation of Lcb. casei N87 starter culture gave similar color parameters and amounts of aldehydes in sausages fermentations without nitrate compared to conventional fermentations with nitrate.

Probiotics in the Sourdough Bread Fermentation: Current Status

Sourdough fermentation is an ancient technique to ferment cereal flour that improves bread quality, bringing nutritional and health benefits. The fermented dough has a complex microbiome composed mainly of lactic acid bacteria and yeasts. During fermentation, the production of metabolites and chemical reactions occur, giving the product unique characteristics and a high sensory quality. Mastery of fermentation allows adjustment of gluten levels, delaying starch digestibility, and increasing the bio-accessibility of vitamins and minerals. This review focuses on the main steps of sourdough fermentation, the microorganisms involved, and advances in bread production with functional properties. The impact of probiotics on human health, the metabolites produced, and the main microbial enzymes used in the bakery industry are also discussed.

Effect of Trehalose and Lactose Treatments on the Freeze-Drying Resistance of Lactic Acid Bacteria in High-Density Culture

Freeze-drying is a commonly used method in commercial preparations of lactic acid bacteria. However, some bacteria are killed during the freeze-drying process. To overcome this, trehalose and lactose are often used as protective agents. Moreover, high-density culture is an efficient way to grow bacterial strains but creates a hypertonic growth environment. We evaluated the effects of trehalose and lactose, as a primary carbon source or as an additive in fermentation, on the freeze-drying survival of Lactobacillus fermentum FXJCJ6-1, Lactobacillus brevis 173-1-2, and Lactobacillus reuteri CCFM1040. Our results showed that L. fermentum FXJCJ6-1 accumulated but did not use intracellular trehalose in a hypertonic environment, which enhanced its freeze-drying resistance. Furthermore, genes that could transport trehalose were identified in this bacterium. In addition, both the lactose addition and lactose culture improved the freeze-drying survival of the bacterium. Further studies revealed that the added lactose might exert its protective effect by attaching to the cell surface, whereas lactose culture acted by reducing extracellular polysaccharide production and promoting the binding of the protectant to the cell membrane. The different mechanisms of lactose and trehalose in enhancing the freeze-drying resistance of bacteria identified in this study will help to elucidate the anti-freeze-drying mechanisms of other sugars in subsequent investigations.

Transcriptome-phenotype matching analysis of how nitrogen sources influence Lacticaseibacillus rhamnosus tolerance to heat stress and oxidative stress

BACKGROUND

Spray drying is the most cost-effective production method for lactic acid bacteria starters, but heat and oxidative stresses result in low survival rates. The heat stress and oxidative stress tolerance of Lacticaseibacillus rhamnosus cultured in tryptone-free MRS (NP-MRS) broth was much stronger than that in MRS or tryptone-free MRS broth supplemented with phenylalanine (Phe-MRS). Here, multiple transcriptome-phenotype matching was performed on cells cultured in NP-MRS, MRS and Phe-MRS broths to reveal the mechanism by which nitrogen sources influence L. rhamnosus tolerance to heat stress and oxidative stress.

RESULTS

Compared with cells cultured in NP-MRS broth, 83 overlapping differentially expressed genes (DEGs) were downregulated by either tryptone or phenylalanine. The overlapping DEGs were mainly classified into carbohydrate metabolism and membrane transport pathways, which are often repressed by glucose during carbon catabolite repression (CCR). In the presence of glucose, the heat stress or oxidative stress tolerance of L. rhamnosus hsryfm 1301 was not strengthened by supplementation with secondary carbohydrates. Replacing glucose with mannose, fructose or ribose improved the heat stress and oxidative stress tolerance of L. rhamnosus hsryfm 1301 (5 to 46-fold).

CONCLUSIONS

Alleviation of CCR might be a reason for the resistance of L. rhamnosus hsryfm 1301 to heat stress and oxidative stress in a low-nitrogen environment. The survival rate of L. rhamnosus during spray drying will hopefully be improved by relieving CCR. It is a new discovery that nitrogen sources influence CCR in L. rhamnosus.

Protective effects of whey protein hydrolysate on Bifidobacterium animalis ssp. lactis Probio-M8 during freeze-drying and storage

We evaluated the potential of whey protein hydrolysate as a lyoprotectant for maintaining the cell viability of Bifidobacterium animalis ssp. lactis Probio-M8 during freeze-drying and subsequent storage. The moisture content and water activity of the lyophilized samples treated by different concentrations of whey protein hydrolysate were ≤5.23 ± 0.33 g/100 g and ≤0.102 ± 0.003, respectively. During storage at 25°C and 30°C, whey protein hydrolysate had a stronger protective effect on B. lactis Probio-M8 than the same concentration of whey protein. Using the Excel tool GinaFit, we estimated the microbial inactivation kinetics during storage. Whey protein hydrolysate reduced cell damage caused by an increase in temperature. Whey protein hydrolysate could protect cells by increasing the osmotic pressure as a compatible solute. Whey protein hydrolysate improved cell membrane integrity and reduced the amounts of reactive oxygen species and malondialdehyde produced. The findings indicated that whey protein hydrolysate was a novel antioxidant lyoprotectant that could protect probiotics during freeze-drying and storage.

Pre-incubation conditions determine the fermentation pattern and microbial community structure in fermenters at mild hydrostatic pressure

Fermentation at elevated hydrostatic pressure is a novel strategy targeting product selectivity. However, the role of inoculum history and cross-resistance, that is, acquired tolerance from incubation under distinctive environmental stress, remains unclear in high-pressure operation. In our here presented work, we studied fermentation and microbial community responses of halotolerant marine sediment inoculum (MSI) and anaerobic digester inoculum (ADI), pre-incubated in serum bottles at different temperatures and subsequently exposed to mild hydrostatic pressure (MHP; < 10 MPa) in stainless steel reactors. Results showed that MHP effects on microbial growth, activity, and community structure were strongly temperature-dependent. At moderate temperature (20°C), biomass yield and fermentation were not limited by MHP; suggesting a cross-resistance effect from incubation temperature and halotolerance. Low temperatures (10°C) and MHP imposed kinetic and bioenergetic limitations, constraining growth and product formation. Fermentation remained favorable in MSI at 28°C and ADI at 37°C, despite reduced biomass yield resulting from maintenance and decay proportionally increasing with temperature. Microbial community structure was modified by temperature during the enrichment, and slight differences observed after MHP-exposure did not compromise functionality. Results showed that the relation incubation temperature-halotolerance proved to be a modifier of microbial responses to MHP and could be potentially exploited in fermentations to modulate product/biomass ratio.

Oral Nanozyme-Engineered Probiotics for the Treatment of Ulcerative Colitis

Background: Probiotic-based therapy for ulcerative colitis (UC) is a novel and promising approach that has gained much popularity in recent years. However, probiotics may be easily captured and destroyed by...