Potential osmoprotectants for the lactic acid bacteria Pediococcus pentosaceus and Tetragenococcus halophila

Ectoine production from a novel bacterial strain and high-purity purification with a cost-effective and single-step method

This study marks the exploration into the production of ectoine, a valuable compound with significant potential as an antioxidant, osmoprotectant, anti-inflammatory agent, and stabilizer of cell membranes, proteins, and DNA integrity. Our focus centred on investigating the presence of ectoine and optimizing its production by the novel ectoine producer bacterial strain, Piscibacillus halophilus. For the optimization of ectoine production the effects of carbon and nitrogen sources, salt, pH, agitation and incubation period were optimized by one-factor-at-a-time. We started with an initial ectoine content of 46.92 mg/L, and through a series of optimization processes, we achieved a remarkable increase, resulting in an ectoine content of 1498.2 mg/L. The bacterial species P. halophilus achieved its highest ectoine production after 48 h of incubation, with conditions set at 10 % (w/v) salinity, pH of 7.50, and an agitation speed of 160 rpm. These precise conditions were found to be the most favourable for maximizing ectoine production by this strain. Besides, we have achieved successful purification of ectoine from the crude extract through a streamlined single-step process. This purification method has delivered an exceptional level of purity, surpassing 99.15 %, and an impressive yield of over 99 %. Importantly, we accomplished this using readily available and cost-effective strong acids (HCl) and strong bases (NaOH) to arrange pH gradients. The use of acid and base in the purification process of ectoine reflects an innovative and sustainable methodology.

Impacts of Ultrasonic Treatment for Black Soybean Okara Culture Medium Containing Choline Chloride on the β-Glucosidase Activity of Lactiplantibacillus plantarum BCRC 10357

The effects of ultrasonic treatment for the culture medium of solid black soybean okara with choline chloride (ChCl) on the survival and β-glucosidase activity of Lactiplantibacillus plantarum BCRC 10357 (Lp-BCRC10357) were investigated. A mixture of 3% dried black soybean okara in de Man-Rogosa-Sharpe (w/v) was used as the Oka medium. With ultrasonic treatment (40 kHz/300 W) of the Oka medium at 60 °C for 3 h before inoculation, the β-glucosidase activity of Lp-BCRC10357 at 12 h and 24 h of incubation amounted to 13.35 and 15.50 U/mL, respectively, which was significantly larger than that (12.58 U/mL at 12 h and 2.86 U/mL at 24 h) without ultrasonic treatment of the medium. This indicated that ultrasonic treatment could cause the microstructure of the solid black soybean okara to be broken, facilitating the transport of ingredients and Lp-BCRC10357 into the internal structure of the okara for utilization. For the effect of ChCl (1, 3, or 5%) added to the Oka medium (w/v) with ultrasonic treatment before inoculation, using 1% ChCl in the Oka medium could stimulate the best response of Lp-BCRC10357 with the highest β-glucosidase activity of 19.47 U/mL in 12 h of incubation, showing that Lp-BCRC10357 had a positive response when confronting the extra ChCl that acted as an osmoprotectant and nano-crowder in the extracellular environment. Furthermore, the Oka medium containing 1% ChCl with ultrasonic treatment led to higher β-glucosidase activity of Lp-BCRC10357 than that without ultrasonic treatment, demonstrating that the ultrasonic treatment could enhance the contact of ChCl and Lp-BCRC10357 to regulate the physiological behavior for the release of enzymes. In addition, the analysis of the isoflavone content and antioxidant activity of the fermented product revealed that the addition of 1% ChCl in the Oka medium with ultrasonic treatment before inoculation allowed a higher enhancement ratio for the biotransformation of isoflavone glycosides to their aglycones, with a slight enhancement in the antioxidant activity at 24 h of fermentation. This study developed a methodology by combining ultrasonic treatment with a limited amount of ChCl to allow the culture medium to acclimate Lp-BCRC10357 and release high levels of β-glucosidase, and this approach has the potential to be used in the fermentation of okara-related products as nutritional supplements in foods.

Inoculation with Lentilactobacillus buchneri alone or in combination with Lentilactobacillus hilgardii modifies gene expression, fermentation profile, and starch digestibility in high-moisture corn

Inoculants combining Lentilactobacillus buchneri and Lentilactobacillus hilgardii have been shown to improve the aerobic stability of high-moisture corn (HMC) and whole-plant corn silage, but the mode of action of this co-inoculation remains to be elucidated. This study used metatranscriptomics to evaluate the effects of inoculation with L. buchneri alone or combined with L. hilgardii on the bacterial community, gene expression, fermentation profile, and starch digestibility in HMC. High-moisture corn not inoculated (Control) or inoculated with L. buchneri NCIMB 40788 (LB) or L. buchneri NCIMB 40788 combined with L. hilgardii CNCM-I-4785 (Combo) was ensiled in mini silo bags for 30, 60, 120, and 180 days. The fermentation profile was evaluated at all time points. Metatranscriptomics was performed on samples collected on day 120. Combo had a greater alpha diversity richness index of contigs than LB and Control, and inoculation with Combo and LB modified the beta-diversity of contigs compared to Control. Out of 69 genes of interest, 20 were differentially expressed in LB compared to Control and 25 in Combo compared to Control. Of those differently expressed genes, 16 (10 of which were associated with carbohydrate metabolism and six with amino acid metabolism) were differently expressed in both LB and Combo compared to Control, and all those genes were upregulated in the inoculated silages. When we compared Combo and LB, we found seven genes expressed differently, four associated with carbohydrate metabolism and downregulated in Combo, and three associated with amino acid metabolism and upregulated in Combo. At day 120, the inoculated silages had more culturable lactic acid bacteria, higher Lactobacillus relative abundance, and lower Leuconostoc relative abundance than Control. The concentration of acetic acid remained low throughout ensiling in Control, but in LB and Combo, it increased up to day 60 and remained stable from day 60 to 180. The 1,2-propanediol was only detected in LB and Combo. Inoculation did not affect the concentration of starch, but starch digestibility was greater in Combo than in Control. Inoculation of HMC with Combo modified the gene expression and fermentation profile compared to Control and LB, improving starch digestibility compared to uninoculated HMC.

Arginine deiminase pathway of Tetragenococcus halophilus contributes to improve the acid tolerance of lactic acid bacteria

Arginine deiminase pathway, controlled by arginine deiminase, ornithine carbamoyltransferase and carbamate kinase, could affect and modulate the intracellular pH homeostasis of lactic acid bacteria under acid stress. Herein, strategy based on exogenous addition of arginine had been proposed to improve the robustness of Tetragenococcus halophilus during acid stressed condition. Results indicated cells cultured in the presence of arginine acquired high tolerance to acid stress mainly through maintaining the homeostasis of intracellular microenvironment. Additionally, metabolomic analysis and q-PCR showed the content of intracellular metabolites and expression levels of genes involved in ADI pathway significantly increased when cells encountered acid stress with the presence of exogenous arginine. Furthermore, Lactococcus lactis NZ9000 with heterologous overexpression of arcA and arcC from T. halophilus exhibited high stress tolerance to acidic condition. This study may provide an insight into the systematical understanding about the mechanism underlying acid tolerance and improve the fermentation performance of LAB during harsh condition.

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.

The Effect of Proline on the Freeze-Drying Survival Rate of Bifidobacterium longum CCFM 1029 and Its Inherent Mechanism

Amino acids, which are important compatible solutes, play a significant role in probiotic lyophilization. However, studies on the functions of Bifidobacterium during freeze-drying are limited. Therefore, in this study, we compared the freeze-drying survival rate of Bifidobacterium longum CCFM 1029 cultivated in different media containing different kinds of compatible solutes. We found that the addition of 21 g/L proline to the culture media substantially improved the freeze-drying survival rate of B. longum CCFM 1029 from 18.61 ± 0.42% to 38.74 ± 1.58%. Interestingly, this change has only been observed when the osmotic pressure of the external culture environment is increased. Under these conditions, we found that proline accumulation in this strain increased significantly. This change also helped the strain to maintain its membrane integrity and the activity of some key enzymes during freeze-drying. Overall, these results show that the addition of proline can help the strain resist a tough environment during lyophilization. The findings of this study provide preliminary data for producers of probiotics who wish to achieve higher freeze-drying survival rates during industrial production.

Health-Promoting Nature of Lactococcus lactis IBB109 and Lactococcus lactis IBB417 Strains Exhibiting Proliferation Inhibition and Stimulation of Interleukin-18 Expression in Colorectal Cancer Cells

Lactic acid bacteria (LAB) are Gram-positive bacteria which are considered for use as adjuvant therapeutics in management of various disease ailments, including obesity, irritable bowel syndrome, lactose intolerance and cancer. To investigate the possible use of Lactococcus lactis strains from our collection in treatment of gastrointestinal cancer, we tested them for the ability to arrest proliferation of human colorectal adenocarcinoma cells (Caco-2). Results of the BrdU assay showed that the anti-proliferative activity of L. lactis cells is strain-specific. We found that particularly, two strains, L. lactis IBB109 and L. lactis IBB417, exhibited the most potent inhibitory effect. Moreover, both strains triggered interleukin 18 gene expression, normally inhibited in Caco-2 (cancer) cells. To examine the probiotic potential of the two strains, we tested them for bile salts and acid tolerance, as well as adhesion properties. Both isolates exhibited probiotic potential—they survived in the presence of 0.3% bile salts and tolerated exposure to low pH and osmotic stress. Notably, we found that L. lactis IBB417 displayed better adherence to mucus and Caco-2 cells than L. lactis IBB109. Additionally, by microdilution tests we confirmed that both strains are sensitive to all nine antibiotics of human and veterinary importance listed by the European Food Safety Authority. Finally, by in silico investigations of whole genome sequencing data, we revealed the genetic features of L. lactis IBB109 and L. lactis IBB417 that can be associated with functional (e.g., adhesion and carbohydrate metabolic genes) and safety (e.g., virulence and antibiotic resistance) aspects of the strains, confirming their health-promoting potential.

Effect of Coix Seed Extracts on Growth and Metabolism of Limosilactobacillus reuteri

Coix seed (Coix lachryma-jobi L.) is an important nourishing food and traditional Chinese medicine. The role of their bioactive constituents in physiology and pharmacology has received considerable scientific attention. However, very little is known about the role of coix seed bioactive components in the growth of Limosilactobacillus reuteri (L. reuteri). This study aimed to evaluate the effects of coix seed extract (CSE) on the growth, acidifying activity, and metabolism of L. reuteri. The results showed that CSE can increase the growth and acidifying activity of L. reuteri compared with the control group. During the stationary phase, the viable bacteria in the medium supplemented with coix seed oil (CSO, 13.72 Log₁₀ CFU/mL), coix polysaccharide (CPO, 12.24 Log₁₀ CFU/mL), and coix protein (CPR, 11.91 Log₁₀ CFU/mL) were significantly higher (p < 0.05) than the control group (MRS, 9.16 Log₁₀ CFU/mL). CSE also enhanced the biosynthesis of lactic acid and acetic acid of L. reuteri. Untargeted metabolomics results indicated that the carbohydrate metabolism, amino acid metabolism, and nucleotide metabolism activities of L. reuteri were increased after adding CSE. Furthermore, CSE increased the accumulation of bioactive metabolites, such as phenyl lactic acid, vitamins, and biotin. Overall, CSE may have prebiotic potential and can be used to culture L. reuteri with high viable bacteria.

Genomic, biochemical and microbial evaluation of probiotic potentials of bacterial isolates from fermented sorghum products

Fermented products, including Ogi-baba and Pito, provide several health benefits, particularly when probiotics are used in the fermentation process. Probiotic microorganisms exert strain-specific health-promoting activities on humans and animals. The objective of this study was to investigate the probiotic potentials of Lactic-acid bacteria (LAB) isolates from indigenous fermented sorghum products (Ogi-baba and Pito). The LAB isolates were screened for potential probiotic properties by antagonistic activity against eight enteropathogenic clinical bacteria isolates (Escherichia coli, Klebsiella sp., Helicobacter pylori, Bacillus sp., Staphylococcus sp., Salmonella sp., Pseudomonas sp. and Listeria monocytogenes) as indicator organisms using the agar well diffusion technique. The organisms were also screened for acidity, bile tolerance, antibiotic susceptibility, production of lactic acid, diacetyl and hydrogen peroxide. β-galactosidase assay was also done. Genomic DNA was extracted from the two selected LAB isolates; the 16S rRNA were amplified and sequenced. The sequence data were subjected to Basic Local Alignment Search Tool (BLAST) and molecular phylogenetic analyses to identify the isolates. The isolates were identified as strains of Lactobacillus plantarum and Pediococcus pentosaceus. The sequence data for these two isolates were submitted to the Genbank with accession numbers KP883298 and KP883297 respectively. The P. pentosaceus strain (PB2) strain exhibited β-galactosidase activity as well as L. plantrum strain (OB6). The study revealed exceptional probiotic potentials of two LAB namely Lactobacillus plantarum strain (OB6) and Pediococcus pentosaceus strain (PB2) isolated from fermented sorghum products, Ogi-baba and Pito respectively. Hence, the two LAB strains may be potentially used as probiotic to prevent some enteropathogen-induced gastrointestinal disorders; reduce the incidence of respiratory tract infections and for the management of lactose in intolerance.

Effect of exogenous proline on the ethanolic tolerance and malolactic performance of Oenococcus oeni

The use of malolactic starter cultures, often offer no guarantee of microbiological success due to the chemical and physical factors (pH, ethanol, SO₂, nutrient availability) that occur during the winemaking process. This study was born with the aim of improving the performance of the lactic acid bacteria used as a starter culture in the de-acidification of wines. Two commercial strains of Oenococcus oeni, were used. Was evaluated the effect of exogenous l-proline added during the bacterial growth, on the improvement of their survival in the presence of different ethanol concentrations and their ability to degrade l-malic acid in synthetic wine with the presence of 12% (v/v) and 13% (v/v) of ethanol. The results showed that l-proline improve ethanol tolerance and so the malolactic performances of O. oeni. This work represents an important strategy to ensure good vitality and improve the performance of the malolactic starter.

Optimizing ectoine biosynthesis using response surface methodology and osmoprotectant applications

PURPOSE

Numerous applications of compatible salts (osmolytes) as ectoine in food and pharmaceutical industries have been intensively increased nowadays. Decreasing the cost of industrial production of ectoine using low-cost cultivation media and improving the yield through modeling procedures are the main scopes of the present study.

METHODS

Three statistical design experiments have been successfully applied for screening the parameters affecting the production process, studying the relations among parameters and optimizing the production using response surface methodology.

RESULTS

A novel semi-synthetic medium based on hydrolyzed corn gluten meal has been developed to cultivate moderate halophilic bacterial strains; Vibrio sp. CS1 and Salinivibrio costicola SH3, and support ectoine synthesis under salinity stress. Two regression equations describe the production process in the new medium have been formulated for each bacterial strain. Response surface optimizer of the central composite model predicts the maximum ectoine production is achieved at incubation time; 63.7 h, pH; 7.47 and salinity; 7.27% for Vibrio sp. CS1 whereas these variables should be adjusted at 56.95 h, 7.089 and 10.34%; on the same order regarding Salinivibrio costicola SH3. In application studies, 50 µg ectoine decreases RBCs hemolysis due to streptolysin O toxin by 21.7% within ten minutes. In addition, 2% ectoine succeeds to increase the viability of lactic acid bacteria in Yogurt as a classic example of functional food during the storage period (7 days).

CONCLUSION

The present study emphasizes on modeling the process of ectoine production by halophilic bacteria as well as its activity as a cryoprotectant agent.

Identification of a GntR family regulator BusRTha and its regulatory mechanism in the glycine betaine ABC transport system of Tetragenococcus halophilus

Glycine betaine is one of the most effective compatible solutes of the halophilic lactic acid bacterium Tetragenococcus halophilus, the transportation of which is essential for its survival under salinity stress condition. In the current study, we attempted to define a glycine betaine ABC transporter system of T. halophilus, busA_Tha, which plays an important role in adapting to salinity condition. The expression of busA_Tha enhanced the growth of the recombinant strain under high salinity. BusR_Tha, a transcription regulator that represses the expression of busA_Tha, was characterized, and the repression was abrogated under high salinity. The binding of the regulator was demonstrated through electrophoretic mobility shift assays, and the binding sites were characterized as 5'-AAA(T/G)TGAC(C/A)(G/A)T(C/A)C-3'. This is the first studied transcription regulator of T. halophilus, and our findings provide insights into the molecular mechanism of halophilic life and tools for further application of halophiles as chassis in industrial biotechnology.

The transcriptomic response of Streptococcus pneumoniae following exposure to cigarette smoke extract

Exposure to cigarette smoke is a risk factor for respiratory diseases. Although most research has focused on its effects on the host, cigarette smoke can also directly affect respiratory pathogens, in some cases enhancing virulence. Streptococcus pneumoniae (the pneumococcus) is a leading cause of community-acquired pneumonia worldwide, however data on the effects of cigarette smoke on the pneumococcus are sparse. Using RNA-seq, we show that pneumococci exposed to cigarette smoke extract in a concentrated acute exposure in vitro model initiate a 'survival' transcriptional response including the upregulation of detoxification enzymes, efflux pumps and osmoregulator transporters, as well as the downregulation of fatty acid and D-alanyl lipoteichoic acid biosynthesis genes. Except for the downregulation of the pneumolysin gene, there were no changes in the expression of major virulence factors following exposure to cigarette smoke. Compared to unexposed pneumococci, smoke-exposed pneumococci did not exhibit any changes in viability, adherence, hydrophobicity or cell lysis susceptibility. In this study, we demonstrate that pneumococci adapt to acute noxious cigarette smoke exposure by inducing a gene expression signature that allows the bacteria to resist its harmful effects.

A partial proteome reference map of Tetragenococcus halophilus and comparative proteomic and physiological analysis under salt stress

Tetragenococcus halophilus, a moderately halophilic Gram-positive lactic acid bacteria, was widely existed in many food fermentation systems, where salt stress is an environmental condition commonly encountered.

Stress Physiology of Lactic Acid Bacteria

Lactic acid bacteria (LAB) are important starter, commensal, or pathogenic microorganisms. The stress physiology of LAB has been studied in depth for over 2 decades, fueled mostly by the technological implications of LAB robustness in the food industry. Survival of probiotic LAB in the host and the potential relatedness of LAB virulence to their stress resilience have intensified interest in the field. Thus, a wealth of information concerning stress responses exists today for strains as diverse as starter (e.g., Lactococcus lactis), probiotic (e.g., several Lactobacillus spp.), and pathogenic (e.g., Enterococcus and Streptococcus spp.) LAB. Here we present the state of the art for LAB stress behavior. We describe the multitude of stresses that LAB are confronted with, and we present the experimental context used to study the stress responses of LAB, focusing on adaptation, habituation, and cross-protection as well as on self-induced multistress resistance in stationary phase, biofilms, and dormancy. We also consider stress responses at the population and single-cell levels. Subsequently, we concentrate on the stress defense mechanisms that have been reported to date, grouping them according to their direct participation in preserving cell energy, defending macromolecules, and protecting the cell envelope. Stress-induced responses of probiotic LAB and commensal/pathogenic LAB are highlighted separately due to the complexity of the peculiar multistress conditions to which these bacteria are subjected in their hosts. Induction of prophages under environmental stresses is then discussed. Finally, we present systems-based strategies to characterize the "stressome" of LAB and to engineer new food-related and probiotic LAB with improved stress tolerance.

Ectoines in cell stress protection: uses and biotechnological production

Microorganisms produce and accumulate compatible solutes aiming at protecting themselves from environmental stresses. Among them, the wide spread in nature ectoines are receiving increasing attention by the scientific community because of their multiple applications. In fact, increasing commercial demand has led to a multiplication of efforts in order to improve processes for their production. In this review, the importance of current and potential applications of ectoines as protecting agents for macromolecules, cells and tissues, together with their potential as therapeutic agents for certain diseases are analyzed and current theories for the understanding of the molecular basis of their biological activity are discussed. The genetic, biochemical and environmental determinants of ectoines biosynthesis by natural and engineered producers are described. The major limitations of current bioprocesses used for ectoines production are discussed, with emphasis on the different microorganisms, environments, molecular engineering and fermentation strategies used to optimize the production and recovery of ectoines. The combined application of both bioprocess and metabolic engineering strategies, allowing a deeper understanding of the main factors controlling the production process is also stated. Finally, this review aims to summarize and update the state of the art in ectoines uses and applications and industrial scale production using bacteria, emphasizing the importance of reactor design and operation strategies, together with the metabolic engineering aspects and the need for feedback between wet and in silico work to optimize bioproduction.

The arginine deiminase pathway of Lactobacillus fermentum IMDO 130101 responds to growth under stress conditions of both temperature and salt

The arginine deiminase (ADI) pathway is a means by which certain sourdough lactic acid bacteria (LAB) convert arginine into ornithine via citrulline while producing ammonia and ATP, thereby coping with acid stress and gaining an energetic advantage. Lactobacillus fermentum IMDO 130101, an isolate from a spontaneous laboratory rye sourdough, possesses an ADI pathway which is modulated by environmental pH. In the present study, a broader view of the activity of the ADI pathway in response to growth under two other commonly encountered stress factors, temperature and added salt, was obtained. In both cases, an increase in ornithine production was observed as a response to growth under both temperature and salt stress conditions. Biokinetic parameters were obtained to describe the kinetics of the ADI pathway as a function of temperature and added salt. The arginine conversion rate increased as a function of added NaCl concentrations but was hardly affected by temperature. In addition, arginine-into-citrulline conversion rate was not affected by temperature but increased with increasing NaCl concentrations. Citrulline-into-ornithine conversion rate increased with increasing temperature, while it dropped to zero with added salt. These findings suggest a more pronounced adaptation of the strain through the ADI pathway to added salt, as compared with different constant temperatures. Furthermore, these results suggest that the ADI pathway in L. fermentum IMDO 130101 is active in adapting to non-optimal growth conditions.

Amino Acid Catabolic Pathways of Lactic Acid Bacteria

Lactic acid bacteria (LAB) constitute a diverse group of Gram positive obligately fermentative microorganisms which include both beneficial and pathogenic strains. LAB generally have complex nutritional requirements and therefore they are usually associated with nutrient-rich environments such as animal bodies, plants and foodstuffs. Amino acids represent an important resource for LAB and their utilization serves a number of physiological roles such as intracellular pH control, generation of metabolic energy or redox power, and resistance to stress. As a consequence, the regulation of amino acid catabolism involves a wide set of both general and specific regulators and shows significant differences among LAB. Moreover, due to their fermentative metabolism, LAB amino acid catabolic pathways in some cases differ significantly from those described in best studied prokaryotic model organisms such as Escherichia coli or Bacillus subtilis. Thus, LAB amino acid catabolism constitutes an interesting case for the study of metabolic pathways. Furthermore, LAB are involved in the production of a great variety of fermented products so that the products of amino acid catabolism are also relevant for the safety and the quality of fermented products.

The compatible-solute-binding protein OpuAC from Bacillus subtilis: ligand binding, site-directed mutagenesis, and crystallographic studies

In the soil bacterium Bacillus subtilis, five transport systems work in concert to mediate the import of various compatible solutes that counteract the deleterious effects of increases in the osmolarity of the environment. Among these five systems, the ABC transporter OpuA, which catalyzes the import of glycine betaine and proline betaine, has been studied in detail in the past. Here, we demonstrate that OpuA is capable of importing the sulfobetaine dimethylsulfonioacetate (DMSA). Since OpuA is a classic ABC importer that relies on a substrate-binding protein priming the transporter with specificity and selectivity, we analyzed the OpuA-binding protein OpuAC by structural and mutational means with respect to DMSA binding. The determined crystal structure of OpuAC in complex with DMSA at a 2.8-A resolution and a detailed mutational analysis of these residues revealed a hierarchy within the amino acids participating in substrate binding. This finding is different from those for other binding proteins that recognize compatible solutes. Furthermore, important principles that enable OpuAC to specifically bind various compatible solutes were uncovered.

Tolerance to high osmolality of the lactic acid bacterium Oenococcus oeni and identification of potential osmoprotectants

Growth of the lactic acid bacterium Oenococcus oeni under hyperosmotic constraint was investigated in a chemically defined medium. The bacterium could grow on media with an elevated osmolality, preferably below 1.5 Osm kg(-)(1) H(2)O. At osmolalities comprised between 0.6 and 1.5 Osm kg(-)(1) H(2)O, the growth deficit elicited by the sugars glucose and fructose was slightly more severe than with salts (NaCl or KCl). In contrast to what was observed in other lactic acid bacteria, proline, glycine betaine and related molecules were unable to relieve inhibition of growth of O. oeni under osmotic constraint. This was correlated to the absence of sequences homologous to the genes coding for glycine betaine and/or proline transporters described in Lactococcus lactis and Lactobacillus plantarum. The amino acid aspartate proved to be osmoprotective under electrolyte and non-electrolyte stress. Examination of the role of peptides during osmoregulation showed that proline- and glutamate-containing peptides were protective under salt-induced stress, and not under sugar-induced stress. Under high salt, PepQ a cytoplasmic prolidase that specifically liberated proline from di-peptides increased activity, while PepX (X-prolyl-dipeptidyl aminopeptidase) and PepI (iminopeptidase) activities were unaffected. Our data suggest that proline- and glutamate-containing peptides may contribute to the adaptation of O. oeni to high salt through their intracellular hydrolysis and/or direct accumulation.

Transcriptional analysis of the acid tolerance response in Streptococcus pneumoniae

Streptococcus pneumoniae, one of the major causes of morbidity and mortality in humans, faces a range of potentially acidic conditions in the middle and late stages of growthin vitro, in diverse human fluids during the infection process, and in biofilms present in the nasopharynx of carriers.S. pneumoniaewas shown to develop a weak acid tolerance response (ATR), where cells previously exposed to sublethal pHs (5·8–6·6) showed an increased survival rate of up to one order of magnitude after challenge at the lethal pH (4·4, survival rate of 10−4). Moreover, the survival after challenge of stationary phase cells at pH 4·4 was three orders of magnitude higher than that of cells taken from the exponential phase, due to the production of lactic acid during growth and increasing acidification of the growth medium until stationary phase. Global expression analysis after short-term (5, 15 and 30 min, the adaptation phase) and long-term (the maintenance phase) acidic shock (pH 6·0) was performed by microarray experiments, and the results were validated by real-time RT-PCR. Out of a total of 126 genes responding to acidification, 59 and 37 were specific to the adaptation phase and maintenance phase, respectively, and 30 were common to both periods. In the adaptation phase, both up- and down-regulation of gene transcripts was observed (38 and 21 genes, respectively), whereas in the maintenance phase most of the affected genes were down-regulated (34 out of 37). Genes involved in protein fate (including those involved in the protection of the protein native structure) and transport (including transporters of manganese and iron) were overrepresented among the genes affected by acidification, 8·7 and 24·6 % of the acid-responsive genes compared to 2·8 % and 9·6 % of the genome complement, respectively. Cross-regulation with the response to oxidative and osmotic stress was observed. Potential regulatory motifs involved in the ATR were identified in the promoter regions of some of the regulated genes.

High tolerance of wild Lactobacillus plantarum and Oenococcus oeni strains to lyophilisation and stress environmental conditions of acid pH and ethanol

A total of 76 Lactobacillus plantarum and Oenococcus oeni wild strains were recovered from traditionally elaborated Spanish red wines and were investigated with respect to their response to acid pH, lyophilisation, temperature and ethanol concentrations which are normally lethal to lactic acid bacteria. Both L. plantarum and O. oeni strains were able to grow at pH 3.2, were highly resistant to lyophilisation treatment and proliferated in the presence of up to 13% ethanol at 18 degrees C. Therefore, it is shown that both species are highly tolerant to stress conditions and that similarly to O. oeni strains, L. plantarum strains are of interest in beverage biotechnology.