Effect of adaptation to ethanol on cytoplasmic and membrane protein profiles of Oenococcus oeni

Regulatory mechanisms of acetic acid, ethanol and high temperature tolerances of acetic acid bacteria during vinegar production

Acetic acid bacteria (AAB) play a pivotal role in the food fermentation industry, especially in vinegar production, due to their ability to partially oxidize alcohols to acetic acid. However, economic bioproduction using AAB is challenged by harsh environments during acetic acid fermentation, among which initial ethanol pressure, subsequent acetic acid pressure, and consistently high temperatures are common experiences. Understanding the stress-responsive mechanisms is essential to developing robust AAB strains. Here, we review recent progress in mechanisms underlying AAB stress response, including changes in cell membrane composition, increased activity of membrane-bound enzymes, activation of efflux systems, and the upregulation of stress response molecular chaperones. We also discuss the potential of advanced technologies, such as global transcription machinery engineering (gTME) and Design-Build-Test-Learn (DBTL) approach, to enhance the stress tolerance of AAB, aiming to improve vinegar production.

Listeria monocytogenes two component system PieRS regulates secretion chaperones PrsA1 and PrsA2 and enhances bacterial translocation across the intestine

Listeria monocytogenes (Lm) is a widespread environmental Gram-positive bacterium that can transition into a pathogen following ingestion by a susceptible host. To cross host barriers and establish infection, Lm is dependent upon the regulated secretion and activity of many proteins including PrsA2, a peptidyl-prolyl cis-trans isomerase with foldase activity. PrsA2 contributes to the stability and activity of a number of secreted virulence factors that are required for Lm invasion, replication, and cell-to-cell spread within the infected host. In contrast, a second related secretion chaperone, PrsA1, has thus far no identified contributions to Lm pathogenesis. Here we describe the characterization of a two-component signal transduction system PieRS that regulates the expression of a regulon that includes the secretion chaperones PrsA1 and PrsA2. PieRS regulated gene products are required for bacterial resistance to ethanol exposure and are important for bacterial survival during transit through the gastrointestinal tract. PrsA1 was also found to make a unique contribution to Lm survival in the GI tract, revealing for the first time a non-overlapping requirement for both secretion chaperones PrsA1 and PrsA2 during the process of intra-gastric infection.

Genomic Analysis of an Excellent Wine-Making Strain Oenococcus oeni SD-2a

Oenococcus oeni is an important microorganism in wine-making-related engineering, and it improves wine quality and stability through malolactic fermentation. Although the genomes of more than 200 O. oeni strains have been sequenced, only a few include completed genome maps. Here, the genome sequence of O. oeni SD-2a, isolated from Shandong, China, has been determined. It is a fully assembled genome sequence of this strain. The complete genome is 1,989,703 bp with a G+C content of 37.8% without a plasmid. The genome includes almost all the essential genes involved in central metabolic pathways and the stress genes reported in other O. oeni strains. Some natural competence-related genes, like comEA, comEC, comFA, comG operon, and comFC, suggest that O. oeni SD-2a may have natural transformation potential. A comparative genomics analysis revealed 730 gene clusters in O. oeni SD-2a homologous to those in four other lactic acid bacteria species (O. oeni PSU-1, O. oeni CRBO-11381, Lactiplantibacillus plantarum UNQLp11, and Pediococcus pentosaceus KCCM40703). A collinearity analysis showed poor collinearity between O. oeni SD-2a and

O. oeni PSU-1, indicating great differences in their evolutionary histories. The results provide general knowledge of O. oeni SD-2a and lay the foundation for specific gene function analyses.

Molecular adaptation response of Oenococcus oeni in non-Saccharomyces fermented wines: A comparative multi-omics approach

Oenococcus oeni is the main agent responsible for malolactic fermentation (MLF) in wine. This usually takes place in red wines after alcoholic fermentation (AF) carried out by Saccharomyces cerevisiae. In recent years, there is an increasing interest in using non-Saccharomyces yeast, usually in combination with S. cerevisiae, to improve wine quality. Current studies report a stimulatory effect of non-Saccharomyces on MLF, generally related to a decrease in the inhibitor compounds found in wine. In this work, we followed a comparative multi-omics approach, including transcriptomic and proteomic analysis, to study the molecular adaptation of O. oeni in wines fermented with Torulaspora delbrueckii and Metschnikowia pulcherrima, two of the most frequently used non-Saccharomyces, in sequential inoculation with S. cerevisiae. We compared the results to the adaptation of O. oeni in S. cerevisiae wine to determine the main changes arising from the use of non-Saccharomyces. The duration of MLF was shortened when using non-Saccharomyces, to half the time with T. delbrueckii and to a quarter with M. pulcherrima. In this work, we observed for the first time how O. oeni responds at molecular level to the changes brought about by non-Saccharomyces. We showed a differential adaptation of O. oeni in the wines studied. In this regard, the main molecular functions affected were amino acid and carbohydrate transport and metabolism, from which peptide metabolism appeared as a key feature under wine-like conditions. We also showed that the abundance of Hsp20, a well-known stress protein, depended on the duration time. Thus, the use of non-Saccharomyces reduced the abundance of Hsp20, which could mean a less stressful wine-like condition for O. oeni.

Clostridium cellulovorans Proteomic Responses to Butanol Stress

Combination of butanol-hyperproducing and hypertolerant phenotypes is essential for developing microbial strains suitable for industrial production of bio-butanol, one of the most promising liquid biofuels. Clostridium cellulovorans is among the microbial strains with the highest potential for direct production of n-butanol from lignocellulosic wastes, a process that would significantly reduce the cost of bio-butanol. However, butanol exhibits higher toxicity compared to ethanol and C. cellulovorans tolerance to this solvent is low. In the present investigation, comparative gel-free proteomics was used to study the response of C. cellulovorans to butanol challenge and understand the tolerance mechanisms activated in this condition. Sequential Window Acquisition of all Theoretical fragment ion spectra Mass Spectrometry (SWATH-MS) analysis allowed identification and quantification of differentially expressed soluble proteins. The study data are available via ProteomeXchange with the identifier PXD024183. The most important response concerned modulation of protein biosynthesis, folding and degradation. Coherent with previous studies on other bacteria, several heat shock proteins (HSPs), involved in protein quality control, were up-regulated such as the chaperones GroES (Cpn10), Hsp90, and DnaJ. Globally, our data indicate that protein biosynthesis is reduced, likely not to overload HSPs. Several additional metabolic adaptations were triggered by butanol exposure such as the up-regulation of V- and F-type ATPases (involved in ATP synthesis/generation of proton motive force), enzymes involved in amino acid (e.g., arginine, lysine, methionine, and branched chain amino acids) biosynthesis and proteins involved in cell envelope re-arrangement (e.g., the products of Clocel_4136, Clocel_4137, Clocel_4144, Clocel_4162 and Clocel_4352, involved in the biosynthesis of saturated fatty acids) and a redistribution of carbon flux through fermentative pathways (acetate and formate yields were increased and decreased, respectively). Based on these experimental findings, several potential gene targets for metabolic engineering strategies aimed at improving butanol tolerance in C. cellulovorans are suggested. This includes overexpression of HSPs (e.g., GroES, Hsp90, DnaJ, ClpC), RNA chaperone Hfq, V- and F-type ATPases and a number of genes whose function in C. cellulovorans is currently unknown.

Ethanol tolerance assessment in recombinant E. coli of ethanol responsive genes from Lactobacillus buchneri NRRL B-30929

We previously identified specific proteins associated with ethanol stress response in a Lactobacillus buchneri strain capable of growing in 10% ethanol. In the current study, the exceptional roles of ethanol responsive genes are examined to determine if they can increase ethanol tolerance in E. coli host cells. The recombinant strains carrying ethanol responsive genes were subjected to growth analyses in media with and without 4% ethanol. Among the expression of these genes and growth analyses of the recombinant strains in ethanol, six genes Lbuc_0522 (NADPH-dependent methylglyoxal reductase), Lbuc_0354 (succinate semialdehyde dehydrogenase), Lbuc_1211(threonyl_tRNA synthetase), Lbuc_2051 (nitroreductase), Lbuc_0707 (branched chain amino acid aminotransferase) and Lbuc_1852 (proline-specific peptidase) conferred host cells tolerance to 4% ethanol. Six genes Lbuc_1523 (phage major capsid protein, HK 97 family), Lbuc_1319 (phosphoglycerate kinase), Lbuc_0787 encoding fumarylacetoacetate hydrolase, Lbuc_1219 encoding UDP-N-acetylmuramate-L-alanine ligase, Lbuc_0466 encoding ornithine carbamoyltransferase and Lbuc_0858 encoding glycine hydroxymethyltransferase showed no impact on growth in media with 4% ethanol with IPTG induction when compared with E. coli carrying control pET28b plasmid. The expression of two genes Lbuc_1557 (S-layer glycoprotein) and Lbuc_2157 (6-phosphogluconate dehydrogenase) resulted ethanol sensitivity phenotype.

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.

Increasing tolerance of hospital Enterococcus faecium to handwash alcohols

Alcohol-based disinfectants and particularly hand rubs are a key way to control hospital infections worldwide. Such disinfectants restrict transmission of pathogens, such as multidrug-resistant Staphylococcus aureus and Enterococcus faecium Despite this success, health care infections caused by E. faecium are increasing. We tested alcohol tolerance of 139 hospital isolates of E. faecium obtained between 1997 and 2015 and found that E. faecium isolates after 2010 were 10-fold more tolerant to killing by alcohol than were older isolates. Using a mouse gut colonization model of E. faecium transmission, we showed that alcohol-tolerant E. faecium resisted standard 70% isopropanol surface disinfection, resulting in greater mouse gut colonization compared to alcohol-sensitive E. faecium We next looked for bacterial genomic signatures of adaptation. Alcohol-tolerant E. faecium accumulated mutations in genes involved in carbohydrate uptake and metabolism. Mutagenesis confirmed the roles of these genes in the tolerance of E. faecium to isopropanol. These findings suggest that bacterial adaptation is complicating infection control recommendations, necessitating additional procedures to prevent E. faecium from spreading in hospital settings.

Increased ethanol tolerance associated with the pntAB locus of Oenococcus oeni and Lactobacillus buchneri

Lactobacillus buchneri and Oenococcus oeni are two unique ethanol-tolerant Gram-positive bacteria species. Genome comparison analyses revealed that L. buchneri and O. oeni possess a pntAB locus that was absent in almost all other lactic acid bacteria (LAB) genomes. Our hypothesis is that the pntAB locus contributes to the ethanol tolerance trait of these two distinct ethanol-tolerant organisms. The pntAB locus, consisting of the pntA and pntB genes, codes for NADP(H) transhydrogenase subunits. This membrane-bound transhydrogenase catalyzes the reduction of NADP+ and is known as an important enzyme in maintaining cellular redox balance. In this study, the transhydrogenase operon from L. buchneri NRRL B-30929 and O. oeni PSU-1 were cloned and analyzed. The LbpntB shared 71.0% identity with the O. oeni (OopntB). The entire pntAB locus was expressed in Lactococcus lactis ssp. lactis IL1403 resulting in an increased tolerance to ethanol (6%), butanol (1.8%) and isopropanol (1.8%) when compared to the control strain. However, the recombinant E. coli cells carrying the entire pntAB locus did not show any improved ethanol tolerance. Independent expression of OopntB and LbpntB in recombinant E. coli BL21(DE3)pLysS host demonstrated higher tolerance to ethanol when compared with a control E. coli BL21(DE3)pLysS strain carrying pET28b vector. Ethanol tolerance comparison of E. coli strains carrying LbpntB and OopntB showed that LbpntB conferred higher ethanol tolerance (4.5%) and resulted in greater biomass, while the OopntB conferred lower ethanol tolerance (4.0%) resulted lower biomass. Therefore, the pntB gene from L. buchneri is a better choice in generating higher ethanol tolerance. This is the first study to uncover the role of pntAB locus on ethanol tolerance.

Co-generation of ethanol and l-lactic acid from corn stalk under a hybrid process

BACKGROUND

Corn stover, as one important lignocellulosic material, has characteristics of low price, abundant output and easy availability. Using corn stover as carbon source in the fermentation of valuable organic chemicals contributes to reducing the negative environmental problems and the cost of production. In ethanol fermentation based on the hydrolysate of corn stover, the conversion rate of fermentable sugars is at a low level because the native S. cerevisiae does not utilize xylose. In order to increase the conversion rate of fermentable sugars deriving from corn stover, an effective and energy saving biochemical process was developed in this study and the residual xylose after ethanol fermentation was further converted to l-lactic acid.

RESULTS

In the hybrid process based on the hydrolysate of corn stover, the ethanol concentration and productivity reached 50.50 g L^-1 and 1.84 g L^-1 h^-1, respectively, and the yield of ethanol was 0.46 g g^-1. The following fermentation of l-lactic acid provided a product titer of 21.50 g L^-1 with a productivity of 2.08 g L^-1 h^-1, and the yield of l-lactic acid was 0.76 g g^-1. By adopting a blank aeration before the inoculation of B. coagulans LA1507 and reducing the final cell density, the l-lactic acid titer and yield reached 24.25 g L^-1 and 0.86 g g^-1, respectively, with a productivity of 1.96 g L^-1 h^-1.

CONCLUSIONS

In this work, the air pumped into the fermentor was used as both the carrier gas for single-pass gas stripping of ethanol and the oxygen provider for the aerobic growth of B. coagulans LA1507. Ethanol was effectively separated from the fermentation broth, while the residual medium containing xylose was reused for l-lactic acid production. As an energy-saving and environmental-friendly process, it introduced a potential way to produce bioproducts under the concept of biorefinery, while making full use of the hydrolysate of corn stover.

Characterization of the antibacterial activity of Bald's eyesalve against drug resistant Staphylococcus aureus and Pseudomonas aeruginosa

Bald's eyesalve is an Anglo-Saxon medicinal remedy that has been used through ancient times to treat eye sty infections and may represent a source of ancientbiotics. This study assessed the efficacy of Bald's eyesalve against several strains of Staphylococcus aureus and Pseudomonas aeruginosa, including a multi-drug resistant phenotype, and identified the principal compound conveying antibacterial activity. Bald's eyesalve formulations were produced by combining garlic, onion or leek, wine, bovine bile, and brass, with specific ingredient omissions in several formulations, followed by incubation at 4 °C for 9 days. Bald's eyesalve formulation ES-GBBr exhibited the greatest antibacterial activity against S. aureus and P. aeruginosa. Fractionation of ES-GBBr using molecular size exclusion and organic solvent partitioning isolated its antibacterial activity to the small molecule nonpolar fraction, and 1D 1H NMR revealed the identity of the antibacterial agent to be allicin. Depletion of allicin from this fraction by addition of exogenous cysteine established that all observable growth inhibition originated from allicin. Quantification of allicin demonstrated that its concentration was significantly greater in ES-GBBr compared to the ES-O formulation; however, this was not due to greater yield. The antibacterial activity of allicin against S. aureus was antagonized by other ingredients within Bald's eyesalve, whereas they were additive or synergistic against P. aeruginosa. These results suggest that neither leek nor onion is necessary for the antibacterial efficacy of Bald's eyesalve against S. aureus or P. aeruginosa, and while allicin was identified as the principal antibacterial agent present, its activity is influenced differentially in the presence of additional Bald's eyesalve ingredients when used against S. aureus compared to P. aeruginosa. Ancientbiotics may provide a source of promising antibacterials; however, identifying the source of activity and assessing distinct formulations for cooperative effects are essential to using ancient remedies, such as Bald's eyesalve, effectively against drug resistant pathogens.

Ethanol stress in Oenococcus oeni: transcriptional response and complex physiological mechanisms

Oenococcus oeni is the dominant species able to cope with a hostile environment of wines, comprising cumulative effects of low pH, high ethanol and SO₂ content, nonoptimal growth temperatures and growth inhibitory compounds. Ethanol tolerance is a crucial feature for the activity of O. oeni cells in wine because ethanol acts as a disordering agent of its cell membrane and negatively affects metabolic activity; it damages the membrane integrity, decreases cell viability and, as other stress conditions, delays the start of malolactic fermentation with a consequent alteration of wine quality. The cell wall, cytoplasmic membrane and metabolic pathways are the main sites involved in physiological changes aimed to ensure an adequate adaptive response to ethanol stress and to face the oxidative damage caused by increasing production of reactive oxygen species. Improving our understanding of the cellular impact of ethanol toxicity and how the cell responds to ethanol stress can facilitate the development of strategies to enhance microbial ethanol tolerance; this allows to perform a multidisciplinary endeavour requiring not only an ecological study of the spontaneous process but also the characterization of useful technological and physiological features of the predominant strains in order to select those with the highest potential for industrial applications.

Mapping the Physiological Response of Oenococcus oeni to Ethanol Stress Using an Extended Genome-Scale Metabolic Model

The effect of ethanol on the metabolism of Oenococcus oeni, the bacterium responsible for the malolactic fermentation (MLF) of wine, is still scarcely understood. Here, we characterized the global metabolic response in O. oeni PSU-1 to increasing ethanol contents, ranging from 0 to 12% (v/v). We first optimized a wine-like, defined culture medium, MaxOeno, to allow sufficient bacterial growth to be able to quantitate different metabolites in batch cultures of O. oeni. Then, taking advantage of the recently reconstructed genome-scale metabolic model iSM454 for O. oeni PSU-1 and the resulting experimental data, we determined the redistribution of intracellular metabolic fluxes, under the different ethanol conditions. Four growth phases were clearly identified during the batch cultivation of O. oeni PSU-1 strain, according to the temporal consumption of malic and citric acids, sugar and amino acids uptake, and biosynthesis rates of metabolic products - biomass, erythritol, mannitol and acetic acid, among others. We showed that, under increasing ethanol conditions, O. oeni favors anabolic reactions related with cell maintenance, as the requirements of NAD(P)⁺ and ATP increased with ethanol content. Specifically, cultures containing 9 and 12% ethanol required 10 and 17 times more NGAM (non-growth associated maintenance ATP) during phase I, respectively, than cultures without ethanol. MLF and citric acid consumption are vital at high ethanol concentrations, as they are the main source for proton extrusion, allowing higher ATP production by F₀F₁-ATPase, the main route of ATP synthesis under these conditions. Mannitol and erythritol synthesis are the main sources of NAD(P)⁺, countervailing for 51-57% of its usage, as predicted by the model. Finally, cysteine shows the fastest specific consumption rate among the amino acids, confirming its key role for bacterial survival under ethanol stress. As a whole, this study provides a global insight into how ethanol content exerts a differential physiological response in O. oeni PSU-1 strain. It will help to design better strategies of nutrient addition to achieve a successful MLF of wine.

Formation of Staphylococcus aureus Biofilm in the Presence of Sublethal Concentrations of Disinfectants Studied via a Transcriptomic Analysis Using Transcriptome Sequencing (RNA-seq)

Staphylococcus aureus is a common biofilm-forming pathogen. Low doses of disinfectants have previously been reported to promote biofilm formation and to increase virulence. The aim of this study was to use transcriptome sequencing (RNA-seq) analysis to investigate global transcriptional changes in S. aureus in response to sublethal concentrations of the commonly used food industry disinfectants ethanol (EtOH) and chloramine T (ChT) and their combination (EtOH_ChT) in order to better understand the effects of these agents on biofilm formation. Treatment with EtOH and EtOH_ChT resulted in more significantly altered expression profiles than treatment with ChT. Our results revealed that EtOH and EtOH_ChT treatments enhanced the expression of genes responsible for regulation of gene expression (sigB), cell surface factors (clfAB), adhesins (sdrDE), and capsular polysaccharides (cap8EFGL), resulting in more intact biofilm. In addition, in this study we were able to identify the pathways involved in the adaptation of S. aureus to the stress of ChT treatment. Further, EtOH suppressed the effect of ChT on gene expression when these agents were used together at sublethal concentrations. These data show that in the presence of sublethal concentrations of tested disinfectants, S. aureus cells trigger protective mechanisms and try to cope with them.IMPORTANCE So far, the effect of disinfectants is not satisfactorily explained. The presented data will allow a better understanding of the mode of disinfectant action with regard to biofilm formation and the ability of bacteria to survive the treatment. Such an understanding could contribute to the effort to eliminate possible sources of bacteria, making disinfectant application as efficient as possible. Biofilm formation plays significant role in the spread and pathogenesis of bacterial species.

Sub-optimal pH Preadaptation Improves the Survival of Lactobacillus plantarum Strains and the Malic Acid Consumption in Wine-Like Medium

Forty-two oenological strains of Lb. plantarum were assessed for their response to ethanol and pH values generally encountered in wines. Strains showed a higher variability in the survival when exposed to low pH (3.5 or 3.0) than when exposed to ethanol (10 or 14%). The study allowed to individuate the highest ethanol concentration (8%) and the lowest pH value (4.0) for the growth of strains, even if the maximum specific growth rate (μ_max) resulted significantly reduced by these conditions. Two strains (GT1 and LT11) preadapted to 2% ethanol and cultured up to 14% of ethanol showed a higher growth than those non-preadapted when they were cultivated at 8% of ethanol. The evaluation of the same strains preadapted to low pH values (5.0 and 4.0) and then grown at pH 3.5 or 3.0 showed only for GT1 a sensitive μ_max increment when it was cultivated in MRS at pH 3 after a preadaptation to pH 5.0. The survival of GT1 and LT11 was evaluated in Ringer's solution at 14% ethanol after a long-term adaptation in MRS with 2% ethanol or in MRS with 2% ethanol acidified at pH 5.0 (both conditions, BC). Analogously, the survival was evaluated at pH 3.5 after a long-term adaptation in MRS at pH 5.0 or in MRS BC. The impact of the physiologic state (exponential phase vs stationary phase) on the survival was also evaluated. Preadapted cells showed the same behavior of non-preadapted cells only when cultures were recovered in the stationary phase. Mathematical functions were individuated for the description of the survival of GT1 and LT11 in MRS at 14% ethanol or at pH 3.5. Finally, a synthetic wine (SW) was used to assess the behavior of Lb. plantarum GT1 and LT11 preadapted in MRS at 2% ethanol or at pH 5.0 or in BC. Only GT1 preadapted to pH 5.0 and collected in the stationary phase showed constant values of microbial counts after incubation for 15 days at 20°C. In addition, after 15 days the L-malic acid resulted completely degraded and the pH value increased of about 0.3 units.

Changes in the Expression of Biofilm-Associated Surface Proteins in Staphylococcus aureus Food-Environmental Isolates Subjected to Sublethal Concentrations of Disinfectants

Sublethal concentrations (sub-MICs) of certain disinfectants are no longer effective in removing biofilms from abiotic surfaces and can even promote the formation of biofilms. Bacterial cells can probably adapt to these low concentrations of disinfectants and defend themselves by way of biofilm formation. In this paper, we report on three Staphylococcus aureus biofilm formers (strong B+++, moderate B++, and weak B+) that were cultivated with sub-MICs of commonly used disinfectants, ethanol or chloramine T, and quantified using Syto9 green fluorogenic nucleic acid stain. We demonstrate that 1.25–2.5% ethanol and 2500 μg/mL chloramine T significantly enhanced S. aureus biofilm formation. To visualize differences in biofilm compactness between S. aureus biofilms in control medium, 1.25% ethanol, or 2500 μg/mL chloramine T, scanning electron microscopy was used. To describe changes in abundance of surface-exposed proteins in ethanol- or chloramine T-treated biofilms, surface proteins were prepared using a novel trypsin shaving approach and quantified after dimethyl labeling by LC-LTQ/Orbitrap MS. Our data show that some proteins with adhesive functions and others with cell maintenance functions and virulence factor EsxA were significantly upregulated by both treatments. In contrast, immunoglobulin-binding protein A was significantly downregulated for both disinfectants. Significant differences were observed in the effect of the two disinfectants on the expression of surface proteins including some adhesins, foldase protein PrsA, and two virulence factors.

Transcriptomic and Proteomic Analysis of Oenococcus oeni Adaptation to Wine Stress Conditions

Oenococcus oeni, the main lactic acid bacteria responsible for malolactic fermentation in wine, has to adapt to stressful conditions, such as low pH and high ethanol content. In this study, the changes in the transcriptome and the proteome of O. oeni PSU-1 during the adaptation period before MLF start have been studied. DNA microarrays were used for the transcriptomic analysis and two complementary proteomic techniques, 2-D DIGE and iTRAQ labeling were used to analyze the proteomic response. One of the most influenced functions in PSU-1 due to inoculation into wine-like medium (WLM) was translation, showing the over-expression of certain ribosomal genes and the corresponding proteins. Amino acid metabolism and transport was also altered and several peptidases were up regulated both at gene and protein level. Certain proteins involved in glutamine and glutamate metabolism showed an increased abundance revealing the key role of nitrogen uptake under stressful conditions. A strong transcriptional inhibition of carbohydrate metabolism related genes was observed. On the other hand, the transcriptional up-regulation of malate transport and citrate consumption was indicative of the use of L-malate and citrate associated to stress response and as an alternative energy source to sugar metabolism. Regarding the stress mechanisms, our results support the relevance of the thioredoxin and glutathione systems in the adaptation of O. oeni to wine related stress. Genes and proteins related to cell wall showed also significant changes indicating the relevance of the cell envelop as protective barrier to environmental stress. The differences found between transcriptomic and proteomic data suggested the relevance of post-transcriptional mechanisms and the complexity of the stress response in O. oeni adaptation. Further research should deepen into the metabolisms mostly altered due to wine conditions to elucidate the role of each mechanism in the O. oeni ability to develop MLF.

A structural comparison of Listeria monocytogenes protein chaperones PrsA1 and PrsA2 reveals molecular features required for virulence

Listeria monocytogenes is a Gram-positive environmental bacterium that lives within soil but transitions into a pathogen upon contact with a mammalian host. The transition of L. monocytogenes from soil dweller to cytosolic pathogen is dependent upon secreted virulence factors that mediate cell invasion and intracellular growth. PrsA1 and PrsA2 are secreted bacterial lipoprotein chaperones that contribute to the folding of proteins translocated across the bacterial membrane; PrsA2 is required for L. monocytogenes virulence, whereas the function of PrsA1 remains to be determined. We have solved an X-ray crystal structure of PrsA1 and have used this model to guide comparison structure-based mutagenesis studies with PrsA2. Targeted mutagenesis of PrsA2 demonstrates that oligomerization of PrsA2 as well as molecular features of the foldase domain are required for protein secretion and virulence, whereas a functional role was uncovered for PrsA1 in bacterial resistance to alcohol. Interestingly, PrsA2 membrane localization is not required for all PrsA2-dependent activities, suggesting that the lipoprotein retains function when released from the bacterial cell. PrsA chaperones are thus multifaceted proteins with distinct domains adapted to accommodate the functional needs of a diverse array of secreted substrates.

Transcriptomic and proteomic analysis of Oenococcus oeni PSU-1 response to ethanol shock

The correct development of malolactic fermentation depends on the capacity of Oenococcus oeni to survive under harsh wine conditions. The presence of ethanol is one of the most stressful factors affecting O. oeni performance. In this study, the effect of ethanol addition (12% vol/vol) on O. oeni PSU-1 has been evaluated using a transcriptomic and proteomic approach. Transcriptomic analysis revealed that the main functional categories of the genes affected by ethanol were metabolite transport and cell wall and membrane biogenesis. It was also observed that some genes were over-expressed in response to ethanol stress (for example, the heat shock protein Hsp20 and a dipeptidase). Proteomic analysis showed that several proteins are affected by the presence of ethanol. Functions related to protein synthesis and stability are the main target of ethanol damage. In some cases the decrease in protein concentration could be due to the relocation of cytosolic proteins in the membrane, as a protective mechanism. The omic approach used to study the response of O. oeni to ethanol highlights the importance of the cell membrane in the global stress response and opens the door to future studies on this issue.

Antioxidant properties of wine lactic acid bacteria: Oenococcus oeni

The most prominent trait of wine lactic acid bacteria (LAB) is their capacity to cope with a hostile environment. However, wine-derived LAB may confer inherent probiotic properties that have not been explored. In this study, the antioxidant activities of 19 strains of Oenococcus oeni were measured in vitro. The results suggested that the antioxidative parameters were widely dispersed, irrespective of the evaluation methods used, which indicated that antioxidative properties depended on the strain and culture medium. The antioxidant mechanisms of O. oeni could be assigned to the 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging ability, reactive oxygen species (ROS) scavenging ability, iron ion chelation (FE), glutathione system, ferric reducing ability of plasma (FRAP), reduction activity (RA), inhibition of ascorbic oxidation (TAA), and linoleic acid oxidation (TLA) abilities. Moreover, most of the O. oeni strains exhibited good survival abilities at low pH values (pH 1.8), simulated intestine juice and bile salts (1 %), suggesting their good adaptation to gastrointestinal conditions and high bile resistance abilities. O. oeni SD-1e, SD-2gf, 31-DH, and SD-2d with promising potential probiotic characteristics were segregated by the principal component analysis (PCA). O. oeni strains likely serve as defensive agents in the intestinal microbial ecosystem and overcome exogenous and endogenous oxidative stress. Although further studies are needed to elucidate the multiple mechanisms involved, the study reported herein confirms the effectiveness of O. oeni in the defense against in vitro oxidative stress.

Effect of the fatty acid composition of acclimated oenological Lactobacillus plantarum on the resistance to ethanol

The aim of this work was to evaluate the changes due to acclimation to ethanol on the fatty acid composition of three oenological Lactobacillus plantarum strains and their effect on the resistance to ethanol and malic acid consumption (MAC). Lactobacillus plantarum UNQLp 133, UNQLp 65.3 and UNQLp 155 were acclimated in the presence of 6 or 10% v/v ethanol, for 48 h at 28°C. Lipids were extracted to obtain fatty acid methyl esters and analysed by gas chromatography interfaced with mass spectroscopy. The influence of change in fatty acid composition on the viability and MAC in synthetic wine was analysed by determining the Pearson correlation coefficient. Acclimated strains showed a significant change in the fatty composition with regard to the nonacclimated strains. Adaptation to ethanol led to a decrease in the unsaturated/saturated ratio, mainly resulting from an increase in the contribution of short-length fatty acid C12:0 and a decrease of C18:1. The content of C12:0 was related to a higher viability after inoculation of synthetic wine. The MAC increased at higher contents in saturated fatty acid, but its efficiency was strain dependent.

Implications of new research and technologies for malolactic fermentation in wine

The initial conversion of grape must to wine is an alcoholic fermentation (AF) largely carried out by one or more strains of yeast, typically Saccharomyces cerevisiae. After the AF, a secondary or malolactic fermentation (MLF) which is carried out by lactic acid bacteria (LAB) is often undertaken. The MLF involves the bioconversion of malic acid to lactic acid and carbon dioxide. The ability to metabolise L-malic acid is strain specific, and both individual Oenococcus oeni strains and other LAB strains vary in their ability to efficiently carry out MLF. Aside from impacts on acidity, LAB can also metabolise other precursors present in wine during fermentation and, therefore, alter the chemical composition of the wine resulting in an increased complexity of wine aroma and flavour. Recent research has focused on three main areas: enzymatic changes during MLF, safety of the final product and mechanisms of stress resistance. This review summarises the latest research and technological advances in the rapidly evolving study of MLF and investigates the directions that future research may take.

A partial proteome reference map of the wine lactic acid bacterium Oenococcus oeni ATCC BAA-1163

Oenococcus oeni is the main lactic acid bacterium that carries out the malolactic fermentation in virtually all red wines and in some white and sparkling wines. Oenococcus oeni possesses an array of metabolic activities that can modify the taste and aromatic properties of wine. There is, therefore, industrial interest in the proteins involved in these metabolic pathways and related transport systems of this bacterium. In this work, we report the characterization of the O. oeni ATCC BAA-1163 proteome. Total and membrane protein preparations from O. oeni were standardized and analysed by two-dimensional gel electrophoresis. Using tandem mass spectrometry, we identified 224 different spots corresponding to 152 unique proteins, which have been classified by their putative function and subjected to bioinformatics analysis.

Effect of acclimation medium on cell viability, membrane integrity and ability to consume malic acid in synthetic wine by oenological Lactobacillus plantarum strains

AIMS

The aim of this work was to evaluate the effect of acclimation on the viability, membrane integrity and the ability to consume malic acid of three oenological strains of Lactobacillus plantarum.

METHODS AND RESULTS

Cultures in the stationary phase were inoculated in an acclimation medium (Accl.) containing 0, 6 or 10% v/v ethanol and incubated 48 h at 28°C. After incubation, cells were harvested by centrifugation and inoculated in a synthetic wine, containing 14% v/v ethanol and pH 3.5 at 28°C. Viability and membrane integrity were determined by flow cytometry (FC) using carboxyfluorescein diacetate (cFDA) and propidium iodide. Bacterial growth and malic acid consumption were monitored in a synthetic wine during 15 days. In nonacclimated strains, the damage of bacterial membranes produced a dramatic decrease in microbial viability in synthetic wine. In contrast, survival of strains previously acclimated in Accl. with 6 and 10% v/v ethanol was noticeable higher. Therefore, acclimation with ethanol increased the cultivability in synthetic wine and consequently, the consumption of l-malic acid after 15 days of growth.

CONCLUSION

Acclimation of oenological strains in media containing ethanol prior to wine inoculation significantly decreases the membrane damage and improves viability in the harsh wine conditions. The role of membrane integrity is crucial to warrant the degradation of l-malic acid.

SIGNIFICANCE AND IMPACT OF THE STUDY

The efficiency of multiparametric FC in monitoring viability and membrane damage along with the malic acid consumption has a strong impact on winemaking because it represents a useful tool for a quick and highly reliable evaluation of oenological parameters.

Enhancement of validamycin A production by addition of ethanol in fermentation of Streptomyces hygroscopicus 5008

The effect of ethanol on the production of the important agro-antibiotic validamycin A (Val-A) in medium containing agricultural by-products was investigated. Under the optimal condition of ethanol addition, the maximal Val-A production titer reached 18 g/L, which increased by 60% compared to the control. To provide an insight into cell response to ethanol, the intracellular reactive oxygen species (ROS), gene transcription and enzyme activity were determined. Intracellular ROS as the molecular signal was increased in the ethanol condition. Global regulators afsR and glnR were involved in regulation of Val-A biosynthesis, and the transcription of eight Val-A structural genes was enhanced. The activity of glucose-6-phosphate dehydrogenase (G6PD) was enhanced while glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was inhibited. A signal transduction cascade from cell signal response to activated transcription of Val-A biosynthetic genes and enhanced antibiotic production is proposed. The information can be helpful for the improvement of large-scale fermentation.

Genetic and physiological studies on Oenococcus oeni PsuI in response to ethanol stress

Malolactate fermentation (MLF), which is known to decreases total acidity and improves the stability and quality of cider is conducted by Oenococcus oeni; the principal microorganism responsible for MLF under stress conditions. Understanding O. oeni physiology in stress conditions can be used to generate tools based on molecular and physiological approaches allowing more precise characterization of strains. Regarding intracellular protein, the results showed an increase in the levels of amino acids under ethanol stress. To study the expressed genes under ethanol stress, one gene were sequenced. An outer-membrane lipoprotein carrier protein precursor, Lo1A was expressed under ethanol stress conditions. Scanning electron microscopy was used to study the effect of ethanol stress on cell morphology. SEM revealed aggregation of bacterial cells as the level of ethanol increases in culture medium in comparison to controls.

Identification of novel genes responsible for ethanol and/or thermotolerance by transposon mutagenesis in Saccharomyces cerevisiae

Saccharomyces cerevisiae strains tolerant to ethanol and heat stresses are important for industrial ethanol production. In this study, five strains (Tn 1-5) tolerant to up to 15% ethanol were isolated by screening a transposon-mediated mutant library. Two of them displayed tolerance to heat (42 °C). The determination of transposon insertion sites and Northern blot analysis identified seven putative genes (CMP2, IMD4, SSK2, PPG1, DLD3, PAM1, and MSN2) and revealed simultaneous down-regulations of CMP2 and IMD4, and SSK2 and PPG1, down-regulation of DLD3, and disruptions of the open reading frame of PAM1 and MSN2, indicating that ethanol and/or heat tolerance can be conferred. Knockout mutants of these seven individual genes were ethanol tolerant and three of them (SSK2, PPG1, and PAM1) were tolerant to heat. Such tolerant phenotypes reverted to sensitive phenotypes by the autologous or overexpression of each gene. Five transposon mutants showed higher ethanol production and grew faster than the control strain when cultured in rich media containing 30% glucose and initial 6% ethanol at 30 °C. Of those, two thermotolerant transposon mutants (Tn 2 and Tn 3) exhibited significantly enhanced growth and ethanol production compared to the control at 42 °C. The genes identified in this study may provide a basis for the application in developing industrial yeast strains.