Changes in glycolytic activity of Lactococcus lactis induced by low temperature

Bacillus cereus Decreases NHE and CLO Exotoxin Synthesis to Maintain Appropriate Proteome Dynamics During Growth at Low Temperature

Cellular proteomes and exoproteomes are dynamic, allowing pathogens to respond to environmental conditions to sustain growth and virulence. Bacillus cereus is an important food-borne pathogen causing intoxication via emetic toxin and/or multiple protein exotoxins. Here, we compared the dynamics of the cellular proteome and exoproteome of emetic B. cereus cells grown at low (16 °C) and high (30 °C) temperature. Tandem mass spectrometry (MS/MS)-based shotgun proteomics analysis identified 2063 cellular proteins and 900 extracellular proteins. Hierarchical clustering following principal component analysis indicated that in B. cereus the abundance of a subset of these proteins—including cold-stress responders, and exotoxins non-hemolytic enterotoxin (NHE) and hemolysin I (cereolysin O (CLO))—decreased at low temperature, and that this subset governs the dynamics of the cellular proteome. NHE, and to a lesser extent CLO, also contributed significantly to exoproteome dynamics; with decreased abundances in the low-temperature exoproteome, especially in late growth stages. Our data therefore indicate that B. cereus may reduce its production of secreted protein toxins to maintain appropriate proteome dynamics, perhaps using catabolite repression to conserve energy for growth in cold-stress conditions, at the expense of virulence.

Influence of culture conditions on the technological properties of Carnobacterium maltaromaticum CNCM I-3298 starters

AIM

The aim of this study is to investigate the effect of a broad spectrum of culture conditions on the acidification activity and viability of Carnobacterium maltaromaticum CNCM I-3298, the main technological properties that determine the shelf-life of biological time-temperature integrator (TTI) labels.

METHODS AND RESULTS

Cells were cultivated at different temperatures (20-37°C) and pH (6-9·5) according to a modified central composite design and harvested at increasing times up to 10 h of stationary phase. Acidification activity and viability of freeze-thawed concentrates were assessed in medium mimicking the biological label. Acidification activity was influenced by all three culture conditions, but pH and harvest time were the most influential. Viability was not significantly affected by the tested range of culture conditions.

CONCLUSIONS

Carnobacterium maltaromaticum CNCM I-3298 must be cultivated at 20°C, pH 6 and harvested at the beginning of stationary phase to exhibit fastest acidification activities. However, if slower acidification activities are pursued, the recommended culture conditions are 30°C, pH 9·5 and a harvest time between 4-6 h of stationary phase.

SIGNIFICANCE AND IMPACT OF THE STUDY

Quantifying the impact of fermentation temperature, pH and harvest time has led to a predictive model for the production of biological TTI covering a broad range of shelf-lives.

Genome-scale analysis of Acetobacterium bakii reveals the cold adaptation of psychrotolerant acetogens by post-transcriptional regulation

Acetogens synthesize acetyl-CoA via CO2 or CO fixation, producing organic compounds. Despite their ecological and industrial importance, their transcriptional and post-transcriptional regulation has not been systematically studied. With completion of the genome sequence of Acetobacterium bakii (4.28-Mb), we measured changes in the transcriptome of this psychrotolerant acetogen in response to temperature variations under autotrophic and heterotrophic growth conditions. Unexpectedly, acetogenesis genes were highly up-regulated at low temperatures under heterotrophic, as well as autotrophic, growth conditions. To mechanistically understand the transcriptional regulation of acetogenesis genes via changes in RNA secondary structures of 5'-untranslated regions (5'-UTR), the primary transcriptome was experimentally determined, and 1379 transcription start sites (TSS) and 1100 5'-UTR were found. Interestingly, acetogenesis genes contained longer 5'-UTR with lower RNA-folding free energy than other genes, revealing that the 5'-UTRs control the RNA abundance of the acetogenesis genes under low temperature conditions. Our findings suggest that post-transcriptional regulation via RNA conformational changes of 5'-UTRs is necessary for cold-adaptive acetogenesis.

Changes in Transcriptome of Yersinia pseudotuberculosis IP32953 Grown at 3 and 28°C Detected by RNA Sequencing Shed Light on Cold Adaptation

Yersinia pseudotuberculosis is a bacterium that not only survives, but also thrives, proliferates, and remains infective at cold-storage temperatures, making it an adept foodborne pathogen. We analyzed the differences in gene expression between Y. pseudotuberculosis IP32953 grown at 3 and 28°C to investigate which genes were significantly more expressed at low temperature at different phases of growth. We isolated and sequenced the RNA from six distinct corresponding growth points at both temperatures to also outline the expression patterns of the differentially expressed genes. Genes involved in motility, chemotaxis, phosphotransferase systems (PTS), and ATP-binding cassette (ABC) transporters of different nutrients such as fructose and mannose showed higher levels of transcripts at 3°C. At the beginning of growth, especially genes involved in securing nutrients, glycolysis, transcription, and translation were upregulated at 3°C. To thrive as well as it does at low temperature, Y. pseudotuberculosis seems to require certain cold shock proteins, especially those encoded by yptb3585, yptb3586, yptb2414, yptb2950, and yptb1423, and transcription factors, like Rho, IF-1, and RbfA, to maintain its protein synthesis. We also found that genes encoding RNA-helicases CsdA (yptb0468), RhlE (yptb1214), and DbpA (yptb1652), which unwind frozen secondary structures of nucleic acids with cold shock proteins, were significantly more expressed at 3°C, indicating that these RNA-helicases are important or even necessary during cold. Genes involved in excreting poisonous spermidine and acquiring compatible solute glycine betaine, by either uptake or biosynthesis, showed higher levels of transcripts at low temperatures. This is the first finding of a strong connection between the aforementioned genes and the cold adaptation of Y. pseudotuberculosis. Understanding the mechanisms behind the cold adaptation of Y. pseudotuberculosis is crucial for controlling its growth during cold storage of food, and will also shed light on microbial cold adaptation in general.

Microbial Metabolism in Soil at Subzero Temperatures: Adaptation Mechanisms Revealed by Position-Specific 13C Labeling

Although biogeochemical models designed to simulate carbon (C) and nitrogen (N) dynamics in high-latitude ecosystems incorporate extracellular parameters, molecular and biochemical adaptations of microorganisms to freezing remain unclear. This knowledge gap hampers estimations of the C balance and ecosystem feedback in high-latitude regions. To analyze microbial metabolism at subzero temperatures, soils were incubated with isotopomers of position-specifically 13C-labeled glucose at three temperatures: +5 (control), -5, and -20°C. 13C was quantified in CO2, bulk soil, microbial biomass, and dissolved organic carbon (DOC) after 1, 3, and 10 days and also after 30 days for samples at -20°C. Compared to +5°C, CO2 decreased 3- and 10-fold at -5 and -20°C, respectively. High 13C recovery in CO2 from the C-1 position indicates dominance of the pentose phosphate pathway at +5°C. In contrast, increased oxidation of the C-4 position at subzero temperatures implies a switch to glycolysis. A threefold higher 13C recovery in microbial biomass at -5 than +5°C points to synthesis of intracellular compounds such as glycerol and ethanol in response to freezing. Less than 0.4% of 13C was recovered in DOC after 1 day, demonstrating complete glucose uptake by microorganisms even at -20°C. Consequently, we attribute the fivefold higher extracellular 13C in soil than in microbial biomass to secreted antifreeze compounds. This suggests that with decreasing temperature, intracellular antifreeze protection is complemented by extracellular mechanisms to avoid cellular damage by crystallizing water. The knowledge of sustained metabolism at subzero temperatures will not only be useful for modeling global C dynamics in ecosystems with periodically or permanently frozen soils, but will also be important in understanding and controlling the adaptive mechanisms of food spoilage organisms.

Lactococci of Local Origin as Potential Starter Cultures for Traditional Montenegrin Cheese Production

The aim of this study is to characterise and examine the biochemical properties of 40 Lactococcus lactis strains isolated from indigenous Montenegrin dairy products in order to explore their potential to be used as starter cultures for producing typical Montenegrin cheese, such as 'bijeli sir', 'masni sir' and 'njeguški sir'. Their safety regarding the production of biogenic amines, the presence of antimicrobial resistance and the antibacterial activity against relevant pathogens and spoilage microorganisms has also been tested. Based on the characterisation, all strains belong to L. lactis ssp. lactis. Out of these 40 strains, 23 displayed rapid acidification ability and proteolysis. However, none of the strains exhibited the ability of lipid degradation. Most of the strains were not associated with any health risk investigated. Summing up, a large percentage (27.5%) of the tested strains showed good properties. These strains should be further examined for their possible application as specific starter cultures in the production of indigenous cheese in Montenegro.

Control of glycolytic flux in directed biosynthesis of uridine-phosphoryl compounds through the manipulation of ATP availability

Adenosine triphosphate (ATP), the most important energy source for metabolic reactions and pathways, plays a vital role in control of metabolic flux. Considering the importance of ATP in regulation of the glycolytic pathway, the use of ATP-oriented manipulation is a rational and efficient route to regulate metabolic flux. In this paper, a series of efficient ATP-oriented regulation methods, such as changing ambient temperature and altering reduced nicotinamide adenine dinucleotide (NADH), was developed. To satisfy the different demand for ATP at different phases in directed biosynthesis of uridine-phosphoryl compounds, a multiphase ATP supply regulation strategy was also used to enhance to yield of target metabolites.

Identification and characterization of lactic Acid bacteria in a commercial probiotic culture

The aim of the present study was to describe the identification and characterization (physiological properties) of two strains of lactic acid bacteria (LAB 18 and 48) present in a commercial probiotic culture, FloraMax(®)-B11. Isolates were characterized morphologically, and identified biochemically. In addition, the MIDI System ID, the Biolog ID System, and 16S rRNA sequence analyses for identification of LAB 18 and LAB 48 strains were used to compare the identification results. Tolerance and resistance to acidic pH, high osmotic concentration of NaCl, and bile salts were tested in broth medium. In vitro assessment of antimicrobial activity against enteropathogenic bacteria and susceptibility to antibiotics were also tested. The results obtained in this study showed tolerance of LAB 18 and LAB 48 to pH 3.0, 6.5% NaCl and a high bile salt concentration (0.6%). Both strains evaluated showed in vitro antibacterial activity against Salmonella enterica serovar Enteritidis, Escherichia coli (O157:H7), and Campylobacter jejuni. These are important characteristics of lactic acid bacteria that should be evaluated when selecting strains to be used as probiotics. Antimicrobial activity of these effective isolates may contribute to efficacy, possibly by direct antimicrobial activity in vivo.

Growth temperature associated protein expression and membrane fatty acid composition profiles of Salmonella enterica serovar Typhimurium

Total cellular proteins and fatty acid composition profiles of mid-log phase cells of Salmonella enterica serovar Typhimurium grown at 8, 25, 37 or 42 °C were separated by 2D-PAGE and FAME analysis. Growth temperature associated protein expression can be grouped into 3 thermal classes which include proteins whose expression is: I) optimal at 37 °C, meaning their expression peaked at 37 °C; II) up-regulated with an increase in growth temperature; III) down-regulated with increase in growth temperature; meaning their expression peaked at 8 °C. At higher growth temperatures, proteins belonging to the functional groups of amino acid transport and metabolism, nucleotide metabolism, energy metabolism and post-translation modifications (chaperones) are present in substantially higher amounts. This increase in abundance is regulated in a temperature dependent manner. It is important to point out that proteins involved in energy metabolism observed in higher amounts at higher growth temperatures all belong to the glycolysis pathway, while at 8 °C they belonged to the TCA cycle. Increase in growth temperatures results in a decrease in membrane fatty acid unsaturation and an increase in saturated and cyclic fatty acids. These results provide an insight into the dynamic molecular and physiological responses of Salmonella Typhimurium during growth at different temperatures.

Characterization of three lactic acid bacteria and their isogenic ldh deletion mutants shows optimization for YATP (cell mass produced per mole of ATP) at their physiological pHs

Several lactic acid bacteria use homolactic acid fermentation for generation of ATP. Here we studied the role of the lactate dehydrogenase enzyme on the general physiology of the three homolactic acid bacteria Lactococcus lactis, Enterococcus faecalis, and Streptococcus pyogenes. Of note, deletion of the ldh genes hardly affected the growth rate in chemically defined medium under microaerophilic conditions. However, the growth rate was affected in rich medium. Furthermore, deletion of ldh affected the ability for utilization of various substrates as a carbon source. A switch to mixed acid fermentation was observed during glucose-limited continuous growth and was dependent on the growth rate for S. pyogenes and on the pH for E. faecalis. In S. pyogenes and L. lactis, a change in pH resulted in a clear change in Y(ATP) (cell mass produced per mole of ATP). The pH that showed the highest Y(ATP) corresponded to the pH of the natural habitat of the organisms.

Adaptation to cold and proteomic responses of the psychrotrophic biopreservative Lactococcus piscium strain CNCM I-4031

There is considerable interest in the use of psychrotrophic bacteria for food biopreservation and in the understanding of cold adaptation mechanisms. The psychrotrophic biopreservative Lactococcus piscium strain CNCM I-4031 was studied for its growth behavior and proteomic responses after cold shock and during cold acclimation. Growth kinetics highlighted the absence of growth latency after cold shock, suggesting a very high promptness in cold adaptation, a behavior that has never been described before for lactic acid bacteria (LAB). A comparative proteomic analysis was applied with two-dimensional gel electrophoresis (2-DE), and upregulated proteins were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Both cold shock and cold acclimation triggered the upregulation of proteins involved in general and oxidative stress responses and fatty acid and energetic metabolism. However, 2-DE profiles and upregulated proteins were different under both conditions, suggesting a sequence of steps in cold adaptation. In addition, the major 7-kDa Csp protein was identified in the L. piscium CNCM I-4031 genome but was not cold regulated. The implication of the identified cold shock proteins and cold acclimation proteins in efficient cold adaptation, the possible regulation of a histidyl phosphocarrier protein, and the roles of a constitutive major 7-kDa Csp are discussed.

NADP-glutamate dehydrogenase activity in nonstarter lactic acid bacteria: effects of temperature, pH and NaCl on enzyme activity and expression

AIMS

To screen the glutamate dehydrogenase (GDH) activity of nonstarter lactic acid bacteria (NSLAB) and to determine the effects of temperature, pH and NaCl values used for cheese ripening on enzyme activity and expression of GDH gene.

METHODS AND RESULTS

A subcellular fractionation protocol and specific enzyme assays were used. The effect of temperature, pH and NaCl on enzyme activity was evaluated. The expression of GDH gene was monitored by real-time PCR. One selected strain was also used as adjunct starter for cheese making to evaluate the catabolism of free amino acids and the production of volatile organic compounds (VOC) during cheese ripening. The cytoplasm fraction of all strains showed in vitro NADP-dependent GDH activity. NADP-GDH activity was markedly strain dependent and varied according to the interactions between temperature, pH and NaCl. Lactobacillus plantarum DPPMA49 showed the highest NADP-GDH activity under temperature, pH and NaCl values found during cheese ripening. RT-PCR analysis revealed that GDH expression of Lact. plantarum DPPMA49 was down-expressed by low temperature (<13°C) and over-expressed by NaCl (1·87-5·62%). According to NADP-GDH activity, the highest level of VOC (alcohols, aldehydes, miscellaneous and carboxylic acids) was found in cheeses made with DPPMA49.

CONCLUSIONS

The results of this study may be considered as an example of the influence of temperature, pH and NaCl on enzyme activity and expression of functional genes, such as GDH, in cheese-related bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

It focuses on the phenotypic and molecular characterization of the NADP-GDH in lactobacilli under cheese-ripening conditions. The findings of this study contribute to the knowledge about enzymes involved in the catabolism of amino acids, to be used as an important selection trait for cheese strains.

Proteomics for the elucidation of cold adaptation mechanisms in Listeria monocytogenes

Listeria monocytogenes, one of the major food-related pathogens, is the aetiological agent of listeriosis, a potentially life-threatening illness. It is able to survive in hostile environments and stress conditions such as those encountered in food-processing technologies (high salt concentration, wide range of pH and temperature, low water availability) and it also thrives at temperatures ranging from -0.4 to 45 °C. In this study, expression proteomics was applied to gain insight into key cellular events that allow L. monocytogenes to survive and multiply even at refrigeration temperatures. Interestingly, we observed that the adaptation processes mainly affect biochemical pathways related to protein synthesis and folding, nutrient uptake and oxidative stress. Furthermore, proteins implicated in metabolic pathways for energy production, such as glycolysis and Pta-AckA pathway, were present to a higher level in the cells grown at 4 °C. This suggests that, on the whole, cells exhibit an enhanced demand for energy to sustain cold growth. Proteomics may represent a key tool in deciphering specific mechanisms underlying cold adaptation response and, more widely, cell machinery.

Proteomic analyses to reveal the protective role of glutathione in resistance of Lactococcus lactis to osmotic stress

Previously, we have shown that glutathione can protect Lactococcus lactis against oxidative stress and acid stress. In this study, we show that glutathione taken up by L. lactis SK11 can protect this organism against osmotic stress. When exposed to 5 M NaCl, L. lactis SK11 cells containing glutathione exhibited significantly improved survival compared to the control cells. Transmission electron microscopy showed that the integrity of L. lactis SK11 cells containing glutathione was maintained for at least 24 h, whereas autolysis of the control cells occurred within 2 h after exposure to this osmotic stress. Comparative proteomic analyses using SK11 cells containing or not containing glutathione that were exposed or not exposed to osmotic stress were performed. The results revealed that 21 of 29 differentially expressed proteins are involved in metabolic pathways, mainly sugar metabolism. Several glycolytic enzymes of L. lactis were significantly upregulated in the presence of glutathione, which might be the key for improving the general stress resistance of a strain. Together with the results of previous studies, the results of this study demonstrated that glutathione plays important roles in protecting L. lactis against multiple environmental stresses; thus, glutathione can be considered a general protectant for improving the robustness and stability of dairy starter cultures.

Inhibition kinetics of catabolic dehydrogenases by elevated moieties of ATP and ADP--implication for a new regulation mechanism in Lactococcus lactis

ATP and ADP inhibit, in varying degrees, several dehydrogenases of the central carbon metabolism of Lactococcus lactis ATCC 19435 in vitro, i.e. glyceraldehyde-3-phosphate dehydrogenase (GAPDH), lactate dehydrogenase (LDH) and alcohol dehydrogenase (ADH). Here we demonstrate mixed inhibition for GAPDH and competitive inhibition for LDH and ADH by adenine nucleotides in single inhibition studies. The nonlinear negative co-operativity was best modelled with Hill-type kinetics, showing greater flexibility than the usual parabolic inhibition equation. Because these natural inhibitors are present simultaneously in the cytoplasm, multiple inhibition kinetics was determined for each dehydrogenase. For ADH and LDH, the inhibitor combinations ATP plus NAD and ADP plus NAD are indifferent to each other. Model discrimination suggested that the weak allosteric inhibition of GAPDH had no relevance when multiple inhibitors are present. Interestingly, with ADH and GAPDH the combination of ATP and ADP exhibits lower dissociation constants than with either inhibitor alone. Moreover, the concerted inhibition of ADH and GAPDH, but not of LDH, shows synergy between the two nucleotides. Similar kinetics, but without synergies, were found for horse liver and yeast ADHs, indicating that dehydrogenases can be modulated by these nucleotides in a nonlinear manner in many organisms. The action of an elevated pool of ATP and ADP may effectively inactivate lactococcal ADH, but not GAPDH and LDH, providing leverage for the observed metabolic shift to homolactic acid formation in lactococcal resting cells on maltose. Therefore, we interpret these results as a regulation mechanism contributing to readjusting the flux of ATP production in L. lactis.

Adaptation and response of Bifidobacterium animalis subsp. lactis to bile: a proteomic and physiological approach

Bile salts are natural detergents that facilitate the digestion and absorption of the hydrophobic components of the diet. However, their amphiphilic nature makes them very inhibitory for bacteria and strongly influences bacterial survival in the gastrointestinal tract. Adaptation to and tolerance of bile stress is therefore crucial for the persistence of bacteria in the human colonic niche. Bifidobacterium animalis subsp. lactis, a probiotic bacterium with documented health benefits, is applied largely in fermented dairy products. In this study, the effect of bile salts on proteomes of B. animalis subsp. lactis IPLA 4549 and its bile-resistant derivative B. animalis subsp. lactis 4549dOx was analyzed, leading to the identification of proteins which may represent the targets of bile salt response and adaptation in B. animalis subsp. lactis. The comparison of the wild-type and the bile-resistant strain responses allowed us to hypothesize about the resistance mechanisms acquired by the derivative resistant strain and about the bile salt response in B. animalis subsp. lactis. In addition, significant differences in the levels of metabolic end products of the bifid shunt and in the redox status of the cells were also detected, which correlate with some differences observed between the proteomes. These results indicate that adaptation and response to bile in B. animalis subsp. lactis involve several physiological mechanisms that are jointly dedicated to reduce the deleterious impact of bile on the cell's physiology.

The Cold Shock Response of Lactobacillus casei: Relation between HPr Phosphorylation and Resistance to Freeze/Thaw Cycles

When carrying out a proteome analysis with a ptsH3 mutant of Lactobacillus casei, we found that the cold shock protein CspA was significantly overproduced compared to the wild-type strain. We also noticed that CspA and CspB of L. casei and CSPs from other organisms exhibit significant sequence similarity to the C-terminal part of EIIA(Glc), a glucose-specific component of the phosphoenolpyruvate:sugar phosphotransferase system. This similarity suggested a direct interaction of HPr with CSPs, as histidyl-phosphorylated HPr has been shown to phosphorylate EIIA(Glc) in its C-terminal part. We therefore compared the cold shock response of several carbon catabolite repression mutants to that of the wild-type strain. Following a shift from 37 degrees C to lower temperatures (20, 15 or 10 degrees C), all mutants showed significantly reduced growth rates. Moreover, glucose-grown mutants unable to form P-Ser-HPr (ptsH1, hprK) exhibited drastically increased sensitivity to freeze/thaw cycles. However, when the same mutants were grown on ribose or maltose, they were similarly resistant to freezing and thawing as the wild-type strain. Although subsequent biochemical and genetic studies did not allow to identify the form of HPr implicated in the resistance to cold and freezing conditions, they strongly suggested a direct interaction of HPr or one of its phospho-derivatives with CspA and/or another, hitherto undetected cold shock protein in L. casei.

Regulation of sugar catabolism in Lactococcus lactis

The increasing number of genomic and post-genomic studies on Gram-positive organisms and especially on lactic acid bacteria brings a lot of information on sugar catabolism in these bacteria. Like for many other bacteria, glucose is the most preferred source of carbon and energy for Lactococcus lactis. Other carbon sources can induce their own utilization in the absence of well-metabolized sugar. These processes engage numbers of genes and undergo complex mechanisms of regulation. In this review, we discuss various biochemical and genetic control mechanisms involved in sugar catabolism, like regulation by repressors, activators, antiterminators or carbon catabolite repression control.

Isolation of lactic acid bacteria from Malaysian foods and assessment of the isolates for industrial potential

Two traditional fermented food 'tapai' (fermented tapioca) and 'tempoyak' (fermented durian flesh), chilli puree and fresh goat's milk were used as sources for the isolation of lactic acid bacteria (LAB). A total of 126 isolates were obtained and by sequential screening for catalase activity and Gram-staining, 55 were determined to be LAB out of which 16 were established to be homofermentative by the gel plug test. Seven isolates were identified by use of the API 50CHL kit and two lactobacilli strains and one lactococci strain were selected to study their growth and lactic acid production profiles in a time course experiment. The lactobacilli strains, both isolated from 'tapai', produced higher amounts of cells and lactic acid from glucose as compared to the lactococci strain isolated from fresh goat's milk.

How phosphotransferase system-related protein phosphorylation regulates carbohydrate metabolism in bacteria

The phosphoenolpyruvate(PEP):carbohydrate phosphotransferase system (PTS) is found only in bacteria, where it catalyzes the transport and phosphorylation of numerous monosaccharides, disaccharides, amino sugars, polyols, and other sugar derivatives. To carry out its catalytic function in sugar transport and phosphorylation, the PTS uses PEP as an energy source and phosphoryl donor. The phosphoryl group of PEP is usually transferred via four distinct proteins (domains) to the transported sugar bound to the respective membrane component(s) (EIIC and EIID) of the PTS. The organization of the PTS as a four-step phosphoryl transfer system, in which all P derivatives exhibit similar energy (phosphorylation occurs at histidyl or cysteyl residues), is surprising, as a single protein (or domain) coupling energy transfer and sugar phosphorylation would be sufficient for PTS function. A possible explanation for the complexity of the PTS was provided by the discovery that the PTS also carries out numerous regulatory functions. Depending on their phosphorylation state, the four proteins (domains) forming the PTS phosphorylation cascade (EI, HPr, EIIA, and EIIB) can phosphorylate or interact with numerous non-PTS proteins and thereby regulate their activity. In addition, in certain bacteria, one of the PTS components (HPr) is phosphorylated by ATP at a seryl residue, which increases the complexity of PTS-mediated regulation. In this review, we try to summarize the known protein phosphorylation-related regulatory functions of the PTS. As we shall see, the PTS regulation network not only controls carbohydrate uptake and metabolism but also interferes with the utilization of nitrogen and phosphorus and the virulence of certain pathogens.

Functional genome-wide analysis of antibody producing NS0 cell line cultivated at different temperatures

Lowering culture temperature has been reported as a significant factor in the improvement of mammalian cell productivity. To determine the physiological changes which take place at different temperature cultivations, an NS0 cell line producing human-mouse chimeric antibody was cultured at 22, 34 and 37 degrees C. Various cellular parameters such as viability, productivity, metabolism, apoptosis and cell cycle were studied and notable changes were shown to be accompanied by changes in metabolic rates. Reduction of the temperature to 22 degrees C resulted in a decrease in the growth rate, inhibition of antibody production, arrest of cell cycle in G2 phase and delay in apoptosis. A slight increase in antibody production was observed at 34 degrees C due to the increase of growth rate and prolonged stationary phase. To better understand and explore the mechanisms underpinning these biological alterations and to identify the genes involved in the genetic reprogramming, genome-wide analyses were performed using GeneChip Mouse Genome arrays. The examination of differential gene expression induced by temperature reduction demonstrated a specific pattern of gene expression in NS0 cells in response to temperature stress. The effect of temperature on transcription induced changes within a wide range of genes involved in metabolic and signalling pathways. Most deregulated genes involved in essential metabolic pathways (i.e. glycolysis/gluconeogenesis, pentose phosphate pathway and inositol metabolism) were repressed in cells cultured at 22 degrees C. By combining gene expression and physiological changes at different temperatures it was possible to provide greater understanding of cell response to hypothermic conditions.

The Phosphotransferase System of Lactobacillus casei: Regulation of Carbon Metabolism and Connection to Cold Shock Response

Genome sequencing of two different Lactobacillus casei strains (ATCC334 and BL23) is presently going on and preliminary data revealed that this lactic acid bacterium possesses numerous carbohydrate transport systems probably reflecting its capacity to proliferate under varying environmental conditions. Many carbohydrate transporters belong to the phosphoenolpyruvate:sugar phosphotransferase system (PTS), but all different kinds of non-PTS transporters are present as well and their substrates are known in a few cases. In L. casei regulation of carbohydrate transport and carbon metabolism is mainly achieved by PTS proteins. Carbon catabolite repression (CCR) is mediated via several mechanisms, including the major P-Ser-HPr/catabolite control protein A (CcpA)-dependent mechanism. Catabolite response elements, the target sites for the P-Ser-HPr/CcpA complex, precede numerous genes and operons. PTS regulation domain-containing antiterminators and transcription activators are also present in both L. casei strains. Their activity is usually controlled by two PTS-mediated phosphorylation reactions exerting antagonistic effects on the transcription regulators: P~EIIB-dependent phosphorylation regulates induction of the corresponding genes and P~His-HPr-mediated phosphorylation plays a role in CCR. Carbohydrate transport of L. casei is also regulated via inducer exclusion and inducer expulsion. The presence of glucose, fructose, etc. leads to inhibition of the transport or metabolism of less favorable carbon sources (inducer exclusion) or to the export of accumulated non-metabolizable carbon sources (inducer expulsion). While P-Ser-HPr is essential for inducer exclusion of maltose, it is not necessary for the expulsion of accumulated thio-methyl-beta-D-galactopyranoside. Surprisingly, recent evidence suggests that the PTS of L. casei also plays a role in cold shock response.

CcpA affects expression of the groESL and dnaK operons in Lactobacillus plantarum

Background

Lactic acid bacteria (LAB) are widely used in food industry and their growth performance is important for the quality of the fermented product. During industrial processes changes in temperature may represent an environmental stress to be overcome by starters and non-starters LAB. Studies on adaptation to heat shock have shown the involvement of the chaperon system-proteins in various Gram-positive bacteria. The corresponding operons, namely the dnaK and groESL operons, are controlled by a negative mechanism involving the HrcA repressor protein binding to the cis acting element CIRCE.

Results

We studied adaptation to heat shock in the lactic acid bacterium Lactobacillus plantarum. The LM3-2 strain, carrying a null mutation in the ccpA gene, encoding the catabolite control protein A (CcpA), showed a lower percent of survival to high temperature with respect to the LM3 wild type strain. Among proteins differentially expressed in the two strains, the GroES chaperon was more abundant in the wild type strain compared to the mutant strain under standard growth conditions. Transcriptional studies showed that class I heat shock operons were differentially expressed upon heat shock in both strains. Indeed, the dnaK and groESL operons were induced about two times more in the LM3 strain compared to the LM3-2 strain. Analysis of the regulatory region of the two operons showed the presence of cre sequences, putative binding sites for the CcpA protein.

Conclusion

The L. plantarum dnaK and groESL operons are characterized by the presence of the cis acting sequence CIRCE in the promoter region, suggesting a negative regulation by the HrcA/CIRCE system, which is a common type of control among the class I heat shock operons of Gram-positive bacteria. We found an additional system of regulation, based on a positive control exerted by the CcpA protein, which would interact with cre sequences present in the regulatory region of the dnaK and groESL operons. The absence of the CcpA protein results in a lower induction of the chaperon coding operons, with a consequent lower percent of survival of the LM3-2 mutant strain population with respect to the wild type when challenged with a heat insult.

Response of Lactobacillus helveticus PR4 to heat stress during propagation in cheese whey with a gradient of decreasing temperatures

The heat stress response was studied in Lactobacillus helveticus PR4 during propagation in cheese whey with a gradient of naturally decreasing temperature (55 to 20 degrees C). Growth under a gradient of decreasing temperature was compared to growth at a constant temperature of 42 degrees C. Proteinase, peptidase, and acidification activities of L. helveticus PR4 were found to be higher in cells harvested when 40 degrees C was reached by a gradient of decreasing temperature than in cells grown at constant temperature of 42 degrees C. When cells grown under a temperature gradient were harvested after an initial exposure of 35 min to 55 degrees C followed by decreases in temperature to 40 (3 h), 30 (5 h 30 min), or 20 degrees C (13 h 30 min) and were then compared with cells grown for the same time at a constant temperature of 42 degrees C, a frequently transient induction of the levels of expression of 48 proteins was found by two-dimensional electrophoresis analysis. Expression of most of these proteins increased following cooling from 55 to 40 degrees C (3 h). Sixteen of these proteins were subjected to N-terminal and matrix-assisted laser desorption ionization-time of flight mass spectrometry analyses. They were identified as stress proteins (e.g., DnaK and GroEL), glycolysis-related machinery (e.g., enolase and glyceraldehyde-3-phosphate dehydrogenase), and other regulatory proteins or factors (e.g., DNA-binding protein II and ATP-dependent protease). Most of these proteins have been found to play a role in the mechanisms of heat stress adaptation in other bacteria.

Differential expression of proteins and genes in the lag phase of Lactococcus lactis subsp. lactis grown in synthetic medium and reconstituted skim milk

We investigated protein and gene expression in the lag phase of Lactococcus lactis subsp. lactis CNRZ 157 and compared it to the exponential and stationary phases. By means of two-dimensional polyacrylamide gel electrophoresis, 28 highly expressed lag-phase proteins, implicated in nucleotide metabolism, glycolysis, stress response, translation, transcription, cell division, amino acid metabolism, and coenzyme synthesis, were identified. Among the identified proteins, >2-fold induction and down-regulation in the lag phase were determined for 12 proteins in respect to the exponential phase and for 18 proteins in respect to the stationary phase. Transcriptional changes of the lag-phase proteins in L. lactis were studied by oligonucleotide microarrays. Good correlation between protein and gene expression studies was demonstrated for several differentially expressed proteins, including nucleotide biosynthetic enzymes, adenylosuccinate synthase (PurA), IMP dehydrogenase (GuaB), and aspartate carbamoyl transferase (PyrB); heat-shock protein DnaK; serine hydroxymethyl transferase (GlyA); carbon catabolite control protein (CcpA); elongation factor G (FusA); and cell division protein (FtsZ).

Listeria monocytogenes ferritin protects against multiple stresses and is required for virulence

In this study, the role of Listeria monocytogenes ferritin was investigated. The fri gene encoding the ferritin was deleted and the phenotype of the mutant was analyzed demonstrating that ferritin is necessary for optimal growth in minimal medium in both presence and absence of iron, as well as after cold- and heat-shock. We also showed that ferritin provides protection against reactive oxygen species and is essential for full virulence of L. monocytogenes. A comparative proteomic analysis revealed an effect of the fri deletion on the levels of listeriolysin O and several stress proteins. Together, our study demonstrates that fri has multiple roles that contribute to Listeria virulence.

10 years of the nisin-controlled gene expression system (NICE) in Lactococcus lactis

Lactococcus lactis is a Gram-positive lactic acid bacterium that, in addition to its traditional use in food fermentations, is increasingly used in modern biotechnological applications. In the last 25 years great progress has been made in the development of genetic engineering tools and the molecular characterization of this species. A new versatile and tightly controlled gene expression system, based on the auto-regulation mechanism of the bacteriocin nisin, was developed 10 years ago-the NIsin Controlled gene Expression system, called NICE. This system has become one of the most successful and widely used tools for regulated gene expression in Gram-positive bacteria. The review describes, after a brief introduction of the host bacterium L. lactis, the fundaments, components and function of the NICE system. Furthermore, an extensive overview is provided of the different applications in lactococci and other Gram-positive bacteria: (1) over-expression of homologous and heterologous genes for functional studies and to obtain large quantities of specific gene products, (2) metabolic engineering, (3) expression of prokaryotic and eukaryotic membrane proteins, (4) protein secretion and anchoring in the cell envelope, (5) expression of genes with toxic products and analysis of essential genes and (6) large-scale applications. Finally, an overview is given of growth and induction conditions for lab-scale and industrial-scale applications.

Proteomic analysis of global changes in protein expression during bile salt exposure of Bifidobacterium longum NCIMB 8809

Adaptation to and tolerance of bile stress are among the main limiting factors to ensure survival of bifidobacteria in the intestinal environment of humans. The effect of bile salts on protein expression patterns of Bifidobacterium longum was examined. Protein pattern comparison of strains grown with or without bile extract allowed us to identify 34 different proteins whose expression was regulated. The majority of these proteins were induced after both a minor (0.6 g liter(-1)) and a major (1.2 g liter(-1)) exposure to bile. These include general stress response chaperones, proteins involved in transcription and translation and in the metabolism of amino acids and nucleotides, and several enzymes of glycolysis and pyruvate catabolism. Remarkably, xylulose 5-phosphate/fructose 6-phosphate phosphoketolase, the key enzyme of the so-called bifidobacterial shunt, was found to be upregulated, and the activity on fructose 6-phosphate was significantly higher for protein extracts of cells grown in the presence of bile. Changes in the levels of metabolic end products (acetate and lactate) were also detected. These results suggest that bile salts, to which bifidobacteria are naturally exposed, induce a complex physiological response rather than a single event in which proteins from many different functional categories take part. This study has extended our understanding of the molecular mechanism underlying the capacity of intestinal bifidobacteria to tolerate bile.

Psychrophilicity of Bacillus psychrosaccharolyticus: a proteomic study

Psychrophilicity of Gram-positive bacterium, Bacillus psychrosaccharolyticus was investigated in a proteomic approach. One hundred and thirty-one protein spots were analyzed by electrospray ionization-quadrupole-time of flight-tandem mass spectrometry and identified using an unpublished translated contig database as well as a nonredundant Gram-positive bacteria protein database from NCBI because of the lack of a genome sequence of this organism. Results focused on proteomic behavior of cold-response show that global up-regulation of metabolic functions and protective mechanism by stress responses might play a major role in psychrophilicity of B. psychrosaccharolyticus.

Effect of the pH of growth on the survival of Lactobacillus delbrueckii subsp. bulgaricus to stress conditions during spray-drying

AIMS

The aim of this study was to optimize survival of Lactobacillus delbrueckii subsp. bulgaricus during spray-drying and subsequent storage through optimizing the pH of growth conditions.

METHODS AND RESULTS

Cell concentrates previously grown without or with pH controlled were spray-dried and stored at 20 degrees C and heat treated at 57 degrees C. Cells grown under noncontrolled pH were more resistant to both drying and heating than cells grown under controlled pH but no significant differences were observed during storage. The intracellular proteins profile of cells grown under both conditions was studied by two-dimensional SDS-polyacrylamide gel electrophoresis. Eight proteins were identified using automated mass spectrometry (MS) and tandem mass spectrometry (MS/MS) data acquisition. Of the identified proteins, only cochaperonin GroES corresponded to a known heat shock protein (HSP). The other proteins identified are proteins involved in glycolysis. For cells grown under noncontrolled pH the expression of the Hsp70, GroES and GroEL, measured by Western blotting, was enhanced.

CONCLUSIONS

The higher resistance of cells grown under noncontrolled pH correlates with the enhanced production of heat shock proteins.

SIGNIFICANCE AND IMPACT OF THE STUDY

Growth of L. bulgaricus under controlled pH (commonly used by the starter cultures production industry) results in cells more sensitive to stresses frequently encountered by the cells during starter cultures preparation/storage/utilization.

Evidence for involvement of at least six proteins in adaptation of Lactobacillus sakei to cold temperatures and addition of NaCl

Lactobacillus sakei is a lactic acid bacterium widely represented in the natural flora of fresh meat. The aim of this study was to analyze the differences in protein expression during environmental changes encountered during technological processes in which L. sakei is involved in order to gain insight into the ability of this species to grow and survive in such environments. Using two-dimensional electrophoresis, we observed significant variation of a set of 21 proteins in cells grown at 4 degrees C or in the presence of 4% NaCl. Six proteins could be identified by determination of their N-terminal sequences, and the corresponding gene clusters were studied. Two proteins belong to carbon metabolic pathways, and four can be clustered as general stress proteins. A phenotype was observed at low temperature for five of the six mutants constructed for these genes. The survival of four mutants during stationary phase at 4 degrees C was affected, and surprisingly, one mutant showed enhanced survival during stationary phase at low temperatures.

Environmental stress responses in Lactobacillus: a review

Environmental stress responses in Lactobacillus, which have been investigated mainly by proteomics approaches, are reviewed. The physiological and molecular mechanisms of responses to heat, cold, acid, osmotic, oxygen, high pressure and starvation stresses are described. Specific examples of the repercussions of these effects in food processing are given. Molecular mechanisms of stress responses in lactobacilli and other bacteria are compared.

Identification of sigma factor sigma B-controlled genes and their impact on acid stress, high hydrostatic pressure, and freeze survival in Listeria monocytogenes EGD-e

The gene encoding the alternative sigma factor sigma(B) in Listeria monocytogenes is induced upon exposure of cells to several stresses. In this study, we investigated the impact of a sigB null mutation on the survival of L. monocytogenes EGD-e at low pH, during high-hydrostatic-pressure treatment, and during freezing. The survival of Delta sigB mutant exponential-phase cells at pH 2.5 was 10,000-fold lower than the survival of EGD-e wild-type cells. Moreover, the Delta sigB mutant failed to show an acid tolerance response. Upon preexposure for 1 h to pH 4.5, the survival at pH 2.5 was 100,000-fold lower for the Delta sigB mutant than for the wild type. The glutamate decarboxylase (GAD) acid resistance system is important in survival and adaptation of L. monocytogenes in acidic conditions. The sigma(B) dependence of the gad genes (gadA, gadB, gadC, gadD, and gadE) was analyzed in silico. Putative sigma(B)-dependent promoter sites were found upstream of the gadCB operon (encoding a glutamate/gamma-aminobutyrate antiporter and a glutamate decarboxylase, respectively) and the lmo2434 gene (gadD, encoding a putative glutamate decarboxylase). Reverse transcriptase PCR revealed that expression of the gadCB operon and expression of gadD are indeed sigma(B) dependent. In addition, a proteomics approach was used to analyze the protein expression profiles upon acid exposure. Although the GAD proteins were not recovered, nine proteins accumulated in the wild type but not in the Delta sigB strain. These proteins included Pfk, GalE, ClpP, and Lmo1580. Exposure to pH 4.5, in order to preload cells with active sigma(B) and consequently with sigma (B)-dependent general stress proteins, also provided considerable protection against high-hydrostatic-pressure treatment and freezing. The combined data argue that the expression of sigma(B)-dependent genes provides L. monocytogenes with nonspecific multiple-stress resistance that may be relevant for survival in the natural environment as well as during food processing.

Increasing acidification of nonreplicating Lactococcus lactis deltathyA mutants by incorporating ATPase activity

Lactococcus lactis MBP71 deltathyA (thymidylate synthase) cannot synthesize dTTP de novo, and DNA replication is dependent on thymidine in the growth medium. In the nonreplicating state acidification by MBP71 was completely insensitive to bacteriophages (M. B. Pedersen, P. R. Jensen, T. Janzen, and D. Nilsson, Appl. Environ. Microbiol. 68:3010-3023, 2002). For nonreplicating MBP71 the biomass increased 3.3-fold over the first 3.5 h, and then the increase stopped. The rate of acidification increased 2.3-fold and then started to decrease. Shortly after inoculation the lactic acid flux was 60% of that of exponentially growing MBP71. However, when nonspecific ATPase activity was incorporated into MBP71, the lactic acid flux was restored to 100% but not above that point, indicating that control over the flux switched from ATP demand to ATP supply (i.e., to sugar transport and glycolysis). As determined by growing nonreplicating cells with high ATPase activity on various sugar sources, it appeared that glycolysis exerted the majority of the control. ATPase activity also stimulated the rate of acidification by nonreplicating MBP71 growing in milk, and pH 5.2 was reached 40% faster than it was without ATPase activity. We concluded that ATPase activity is a functional means of increasing acidification by nonreplicating L. lactis.

Lactic acid bacteria and proteomics: current knowledge and perspectives

Lactic acid bacteria (LAB) are widely used in the agro-food industry. Some of the LAB also participate in the natural flora in humans and animals. We review here proteomic studies concerning LAB. Two methods of research can be distinguished. In the first one, a systematic mapping of proteins is attempted, which will be useful for taxonomy and to function assignment of proteins. The second one focuses particularly on proteins whose synthesis is induced by various environmental situations or stresses. However, both approaches are complementary and will give new insights for the use of bacteria in industry, in human health and in the struggle against bacterial pathogens. Interest in LAB is growing, showing thus an increasing concern of their rational use and one can foresee in the near future an increasing use of proteomics as well as genomics.

Salt stress proteins induced in Listeria monocytogenes

The ability of Listeria monocytogenes to tolerate salt stress is of particular importance, as this pathogen is often exposed to such environments during both food processing and food preservation. In order to understand the survival mechanisms of L. monocytogenes, an initial approach using two-dimensional polyacrylamide gel electrophoresis was performed to analyze the pattern of protein synthesis in response to salt stress. Of 400 to 500 visible proteins, the synthesis of 40 proteins (P < 0.05) was repressed or induced at a higher rate during salt stress. Some of the proteins were identified on the basis of mass spectrometry or N-terminal sequence analysis and database searching. Twelve proteins showing high induction after salt stress were similar to general stress proteins (Ctc and DnaK), transporters (GbuA and mannose-specific phosphotransferase system enzyme IIAB), and general metabolism proteins (alanine dehydrogenase, CcpA, CysK, EF-Tu, Gap, GuaB, PdhA, and PdhD).

The functional ccpA gene is required for carbon catabolite repression in Lactobacillus plantarum

We report the characterization of the ccpA gene of Lactobacillus plantarum, coding for catabolite control protein A. The gene is linked to the pepQ gene, encoding a proline peptidase, in the order ccpA-pepQ, with the two genes transcribed in tandem from the same strand as distinct transcriptional units. Two ccpA transcription start sites corresponding to two functional promoters were found, expression from the upstream promoter being autogenously regulated through a catabolite-responsive element (cre) sequence overlapping the upstream +1 site. During growth on ribose, the upstream promoter showed maximal expression, while growth on glucose led to transcription from the downstream promoter. In a ccpA mutant strain, the gene was transcribed mainly from the upstream promoter in both repressing and non repressing conditions. Expression of two enzyme activities, beta-glucosidase and beta-galactosidase, was relieved from carbon catabolite repression in the ccpA mutant strain. In vivo footprinting analysis of the catabolite-controlled bglH gene regulatory region in the ccpA mutant strain showed loss of protection of the cre under repressing conditions.