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

Significant influence of four highly conserved amino-acids in lipochaperon-active sHsps on the structure and functions of the Lo18 protein

To cope with environmental stresses, bacteria have developed different strategies, including the production of small heat shock proteins (sHSP). All sHSPs are described for their role as molecular chaperones. Some of them, like the Lo18 protein synthesized by Oenococcus oeni, also have the particularity of acting as a lipochaperon to maintain membrane fluidity in its optimal state following cellular stresses. Lipochaperon activity is poorly characterized and very little information is available on the domains or amino-acids key to this activity. The aim in this paper is to investigate the importance at the protein structure and function level of four highly conserved residues in sHSP exhibiting lipochaperon activity. Thus, by combining in silico, in vitro and in vivo approaches the importance of three amino-acids present in the core of the protein was shown to maintain both the structure of Lo18 and its functions.

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.

Evaluation of a Witch Hazel Extract for the Potential Prebiotic and Protective Effect on Select Lactiplantibacillus plantarum (Prev. Lactobacillus plantarum) Strains

Witch hazel extract has been evaluated in prior studies demonstrating the phenolic-mediated biofilm inhibition, toxin production inhibition, and growth inhibition in Staphylococcus aureus. In this study, we are evaluating the possible prebiotic and protective effect of witch hazel extract on select probiotic Lactiplantibacillus plantarum strains, namely L. plantarum LP 10241 and L. plantarum LPBAA-793. When the prebiotic effect was evaluated, we observed that the tested extract had prebiotic effect at the higher tested dose (0.5%) on LPBAA-793 strain (8.7 log CFU/mL after 18 h compared to 5.1 log CFU/mL with the control) and on LP 10241 strain (7.7 log CFU/mL after 18 h compared to 4.4 log CFU/mL with the control). For the evaluation of the protective effect of witch hazel extract on the select strains, we subjected nutrient depletion stress under aerobic conditions and monitored the cell death with and without addition of witch hazel extract. We observed that the tested extract had a significant protective effect on LPBAA-793 strain (4 log CFU/mL after 12 days, compared to no growth with control) and a slighter protective effect against LP 10241 strains (6.3 log CFU/mL in day 2 compared to 4.3 log CFU/mL with control). The results from this research provide for the first time the rationale that while witch hazel extract has significant antimicrobial, anti-toxin production and anti-biofilm activities on pathogenic microorganisms, it might play an important and positive role on health-beneficial probiotic bacteria.

Analysis of Transcriptomic Response to SO2 by Oenococcus oeni Growing in Continuous Culture

To successfully complete malolactic fermentation (MLF), Oenococcus oeni must overcome wine stress conditions of low pH, high ethanol, and the presence of SO2. Failure to complete MLF may result in detrimental effects to the quality and stability of the resulting wines. Research efforts to date have focused on elucidating the mechanisms and genetic features that confer the ability to withstand low pH and high ethanol concentrations on O. oeni; however, the responses to SO2 stress are less well defined. This study focused on characterizing the transcriptional response of O. oeni to SO2 challenge during cultivation in a continuous system at wine-like pH (3.5). This experimental design allowed the precise discrimination of transcriptional changes linked to SO2 stress from responses associated with growth stage and cultivation parameters. Differential gene expression analysis revealed major transcriptional changes following SO2 exposure and suggested that this compound primarily interacts with intracellular proteins, DNA, and the cell envelope of O. oeni. The molecular chaperone hsp20, which has a demonstrated function in the heat, ethanol, and acid stress response, was highly upregulated, confirming its additional role in the response of this species to SO2 stress. This work also reports the first nanopore-based complete genome assemblies for O. oeni. IMPORTANCE Malolactic fermentation is an indispensable step in the elaboration of most wines and is generally performed by Oenococcus oeni, a Gram-positive heterofermentative lactic acid bacterium species. While O. oeni is tolerant to many of the wine stresses, including low pH and high ethanol concentrations, it has high sensitivity to SO2, an antiseptic and antioxidant compound regularly used in winemaking. Understanding the physiological changes induced in O. oeni by SO2 stress is essential for the development of more robust starter cultures and methods for their use. This study describes the main transcriptional changes induced by SO2 stress in the wine bacterium O. oeni and provides foundational understanding on how this compound interacts with the cellular components and the induced protective mechanisms of this species.

Oenococcus oeni Lifestyle Modulates Wine Volatilome and Malolactic Fermentation Outcome

In this study, nine Oenococcus oeni strains were tested for their ability to adhere to polystyrene using mMRS and wine as culture media. Moreover, planktonic and biofilm-detached cells were investigated for their influence on malic acid degradation kinetics and aroma compound production. Three strains were able to adhere on polystyrene plates in a strain-dependent way. In particular, MALOBACT-T1 and ISO359 strains mainly grew as planktonic cells, while the ISO360 strain was found prevalent in sessile state. The strain-dependent adhesion ability was confirmed by confocal laser scanning microscopy. Planktonic and biofilm detached cells showed a different metabolism. In fact, biofilm-detached cells had a better malic acid degradation kinetic and influenced the aroma composition of resulting wines, acting on the final concentration of esters, higher alcohols, and organic acids. Oenococcus oeni in biofilm lifestyle seems to be a suitable tool to improve malolactic fermentation outcome, and to contribute to wine aroma. The industrial-scale application of this strategy should be implemented to develop novel wine styles.

Heat Adaptation Induced Cross Protection Against Ethanol Stress in Tetragenococcus halophilus: Physiological Characteristics and Proteomic Analysis

Ethanol is a toxic factor that damages membranes, disturbs metabolism, and may kill the cell. Tetragenococcus halophilus, considered as the cell factory during the manufacture of traditional fermented foods, encounters ethanol stress, which may affect the viability and fermentative performance of cells. In order to improve the ethanol tolerance of T. halophilus, a strategy based on cross protection was proposed in the current study. The results indicated that cross protection induced by heat preadaptation (45°C for 1.5 h) could significantly improve the stress tolerance (7.24-fold increase in survival) of T. halophilus upon exposure to ethanol (10% for 2.5 h). Based on this result, a combined analysis of physiological approaches and TMT-labeled proteomic technology was employed to investigate the protective mechanism of cross protection in T. halophilus. Physiological analysis showed that the heat preadapted cells exhibited a better surface phenotype, higher membrane integrity, and higher amounts of unsaturated fatty acids compared to unadapted cells. Proteomic analysis showed that a total of 163 proteins were differentially expressed in response to heat preadaptation. KEGG enrichment analysis showed that energy metabolism, membrane transport, peptidoglycan biosynthesis, and genetic information processing were the most abundant metabolic pathways after heat preadaptation. Three proteins (GpmA, AtpB, and TpiA) involved in energy metabolism and four proteins (ManM, OpuC, YidC, and HPr) related to membrane transport were up-regulated after heat preadaptation. In all, the results of this study may help understand the protective mechanisms of preadaptation and contribute to the improvement of the stress resistance of T. halophilus during industrial processes.

Influences of acid and ethanol stresses on Oenococcus oeni SD-2a and its proteomic and transcriptional responses

BACKGROUND

During winemaking, malolactic fermentation (MLF) is usually induced by Oenococcus oeni owing to its high resistance to wine stress factors. To ensure a controlled and efficient MLF process, starter cultures are inoculated in wine. In previous studies, O. oeni strains with sub-lethal acid or ethanol stresses showed higher freeze-drying vitality and better MLF performance. To explore the mechanisms involved, influences of acid and ethanol stresses on O. oeni SD-2a were investigated in this study to gain a better understanding of the cross-protection responses.

RESULTS

The results showed that acid and ethanol stresses both caused damage to cell membranes and decreased cellular adenosine triphosphate concentration. At the same time, acid stress increased the uptake of glutathione, while ethanol stress led to cell depolarization. The results of comparative proteomic analysis highlighted that heat shock protein was induced with almost all acid and ethanol stresses. In addition, the expression of stress-relevant genes (hsp20, clpP, trxA, ctsR, recO, usp) increased greatly with ethanol and acid stress treatments. Finally, the viability of O. oeni was improved with acid and ethanol pretreatments after freeze-drying.

CONCLUSIONS

This study demonstrated that acid and ethanol stresses had mixed influences on O. oeni SD-2a. Some physiological and molecular changes would contribute to a more stress-tolerant state of O. oeni, thereby improving the viability of lyophilized cells. © 2020 Society of Chemical Industry.

Increasing Solvent Tolerance to Improve Microbial Production of Alcohols, Terpenoids and Aromatics

Fuels and polymer precursors are widely used in daily life and in many industrial processes. Although these compounds are mainly derived from petrol, bacteria and yeast can produce them in an environment-friendly way. However, these molecules exhibit toxic solvent properties and reduce cell viability of the microbial producer which inevitably impedes high product titers. Hence, studying how product accumulation affects microbes and understanding how microbial adaptive responses counteract these harmful defects helps to maximize yields. Here, we specifically focus on the mode of toxicity of industry-relevant alcohols, terpenoids and aromatics and the associated stress-response mechanisms, encountered in several relevant bacterial and yeast producers. In practice, integrating heterologous defense mechanisms, overexpressing native stress responses or triggering multiple protection pathways by modifying the transcription machinery or small RNAs (sRNAs) are suitable strategies to improve solvent tolerance. Therefore, tolerance engineering, in combination with metabolic pathway optimization, shows high potential in developing superior microbial producers.

Phytochemical Profile of Capsicum annuum L. cv Senise, Incorporation into Liposomes, and Evaluation of Cellular Antioxidant Activity

Overproduction of oxidants in the human body is responsible for oxidative stress, which is associated with several diseases. High intake of vegetables and fruits can reduce the risk of chronic diseases, as they are sources of bioactive compounds capable of contrasting the free radical effects involved in cancer, obesity, diabetes, and neurodegenerative and cardiovascular diseases. Capsicum annuum L. cv Senise is a sweet pepper that is grown in the Basilicata region (Italy). It is an important source of polyphenols, carotenoids, and capsinoids and can play a key role in human health. In this study, an ethanol extract was obtained from C. annuum dried peppers and the analysis of the phytochemical composition was performed by LC-ESI/LTQ Orbitrap/MS. The extract was incorporated into liposomes, which showed small size (~80 nm), good homogeneity, negative surface charge, and good stability in storage. The biological activity of the extract was evaluated in the human hepatoma (HepG2) cell line, used as model cells. The extract showed no cytotoxic activity and reduced the intracellular reactive oxygen species (ROS) level in stressed cells. The antioxidant activity was further improved when the extract was loaded into liposomes. Moreover, the extract promoted the expression of endogenous antioxidants, such as catalase, superoxide dismutase, and glutathione peroxidase through the Nrf-2 pathway evaluated by RT-PCR.

Heterologous expression of ctsR from Oenococcus oeni enhances the acid-ethanol resistance of Lactobacillus plantarum

Oenococcus oeni is a lactic acid bacterium that is widely used in wine-making to conduct malolactic fermentation (MLF). During MLF, O. oeni undergoes acid and ethanol stress that impairs its growth. In order to investigate the role that the ctsR gene plays in acid-ethanol stress, the ctsR gene from O. oeni was expressed heterologously in L. plantarum. The transcription level of the ctsR gene and 10 additional stress response genes in L. plantarum were analyzed by RT-qPCR. Physiological assays to assess ROS accumulation, cell membrane integrity, intracellular ATP and GSH levels, Ca2+/Mg2+-ATPase and Na+/K+-ATPase activities were also performed. Results showed that the recombinant strain WCFS1-CtsR exhibited stronger growth performance than the control strain WCFS1-Vector, and the expression of ctsR, clp, and hsp genes were significantly increased under acid-ethanol stress. Furthermore, WCFS1-CtsR displayed 1.08-, and 1.39-fold higher ATP and GSH concentrations, respectively, compared to the corresponding values for WCFS1-Vector under acid-ethanol stress. ROS accumulation and PI value of WCFS1-CtsR were decreased by 46.52% and 42.80%, respectively, compared to the control strain. In addition, the two ATPase activities in WCFS1-CtsR increased significantly compared with WCFS1-Vector. This is the first report demonstrating that ctsR gene enhances the acid-ethanol tolerance of L. plantarum.

The impacts of Schizosaccharomyces on winemaking

In the past century, yeasts from the genus Saccharomyces represented the only option in fermentation industries, such as winemaking, to produce wine, beer, and other fermented products. However, other genera are currently emerging to solve challenges in modern enology. Schizosaccharomyces pombe is showing promising results in solving specific challenges in northern, cool viticulture regions with highly acidic wines by deacidifying these wines through its malic acid metabolism. In addition, this microorganism is considered beneficial in warm growing regions with challenges such as the control of wine food safety problems such as the presence of biogenic amines, ochratoxin A, or ethyl carbamate. Indeed, the genus Schizosaccharomyces positively influences other important wine quality parameters, such as color and polysaccharide content. However, the main challenge of using this genus remains the selection of proper strains that alleviate problems such as the production of high acetate concentrations. Industries other than wine production such as ginger fermentation, apple wine, Kei-apple fermentation, plum wine, sparkling wine, and bilberry fermentation industries have also started to study Schizosaccharomyces species as an alternative tool for solving specific related problems. The review discusses the influence of Schizosaccharomyces on different fermentation quality parameters and its main applications in different industries.

Production and Antimicrobial Activity of Nisin Under Enological Conditions

Lactic acid bacteria (LAB) are responsible for the malolactic fermentation of wines, and, therefore, controlling the growth of these bacteria is a key factor for elaborating premium wines. Sulfur dioxide has been traditionally used as an efficient antimicrobial and antioxidant agent, however, nowadays consumers' demand tends toward a reduction of sulfur dioxide levels in wine and other fermented foods. A previous study of our research group had demonstrated the effectiveness of the bacteriocin nisin to inhibit the growth of enological LAB, and its activity had been tested in culture broths. The aim of this study was to investigate the possibility of controlling the growth of bacteria in wine by the use of nisin in combination with sulfur dioxide, and to study nisin production by the natural producer Lactococcus lactis LM29 under enological conditions. Our results showed that L. lactis LM29 produced nisin in the presence of 2 and 4% ethanol (v/v), while higher concentrations of ethanol fully inhibited the production of nisin. We obtained a nisin enriched active extract (NAE) from the cell-free supernatant of a culture of L. lactis LM29 in MRS broth containing 60% (v/v) sterile grape juice, and the extract was fully active in inhibiting the growth of the enological LAB tested by the microtiter method. Moreover, the nisin concentration of the obtained NAE could actually prevent the formation of an undesirable biofilm of LAB strains. Finally, our results of wine ageing under winery conditions showed that the use of 50 mg/L nisin decreased fourfold the concentration of sulfur dioxide required to prevent LAB growth in the wines.

Oenococcus oeni Exopolysaccharide Biosynthesis, a Tool to Improve Malolactic Starter Performance

Oenococcus oeni is the lactic acid bacterium that most commonly drives malolactic fermentation (MLF) in wine. Though the importance of MLF in terms of wine microbial stability and sensory improvement is well established, it remains a winemaking step not so easy to control. O. oeni displays many adaptation tools to resist the harsh wine conditions which explain its natural dominance at this stage of winemaking. Previous findings showed that capsular polysaccharides and endogenous produced dextran increased the survival rate and the conservation time of malolactic starters. In this paper, we showed that exopolysaccharides specific production rates were increased in the presence of single stressors relevant to wine (pH, ethanol). The transcription of the associated genes was investigated in distinct O. oeni strains. The conditions in which eps genes and EPS synthesis were most stimulated were then evaluated for the production of freeze dried malolactic starters, for acclimation procedures and for MLF efficiency. Sensory analysis tests on the resulting wines were finally performed.