Heterologous Expression of Argininosuccinate Synthase From Oenococcus oeni Enhances the Acid Resistance of Lactobacillus plantarum

Interaction between acid-tolerant alga Graesiella sp. MA1 and schwertmannite under long-term acidic condition

Schwertmannite (Sch), a typical Fe(III)-oxyhydroxysulphate mineral, is the precipitation reservoir of toxic elements in acid mine drainage (AMD). Acid-tolerant microbes in AMD can participate in the microbe-mediated transformation of Sch, while Sch affects the physiological characteristics of these acid-tolerant microbes. Based on our discovery of algae and Sch enrichment in a contaminated acid mine pit lake, we predicted the interaction between algae and Sch when incubated together. The acid-tolerant alga Graesiella sp. MA1 was isolated from the pit-lake surface water of an acidic mine and incubated with different contents of Sch. Sch was detected as the main product at the end of 81 d; however, there was a weak transformation. The presence of dissolved Fe(II) could be largely attributed to the photoreduction dissolution of Sch, which was promoted by Graesiella sp. MA1. The adaptation and growth phases of Graesiella sp. MA1 differed under Sch stress. The photosynthetic and metabolic activities increased and decreased at the adaptation and growth phases, respectively. The MDA contents and antioxidant activity of SOD, APX, and GSH in algal cells gradually enhanced as the Sch treatment content increased, indicating a defense strategy of Graesiella sp. MA1. Metabolomic analysis revealed that Sch affected the expression of significant differential metabolites in Graesiella sp. MA1. Organic carboxylic acid substances were essentially up-regulated in response to Sch stress. They were abundant in the medium-Sch system with the highest Fe(III) reduction, capable of complexing Fe(III), and underwent photochemical reactions via photo-induced charge transfer. The significant up-regulation of reducing sugars revealed the high energy requirement of Graesiella sp. MA1 under Sch stress. And first enriched KEGG pathway demonstrated the importance of sugar metabolism in Graesiella sp. MA1. Data acquired in this study provide novel insights into extreme acid stress adaptation of acid-tolerant algae and Sch, contributing to furthering understanding of AMD environments.

Improved Tolerance of Lactiplantibacillus plantarum in the Presence of Acid by the Heterologous Expression of trxA from Oenococcus oeni

Oenococcus oeni is the main microorganism that undergoes malolactic fermentation (MLF) in the winemaking industry due to its excellent adaptability to harsh wine environments. The start of MLF is often delayed or even fails, and low pH appears to be a crucial parameter. To study the function of the trxA gene in acid stress, a plasmid containing the trxA gene of O. oeni SD-2a was heterologously expressed in Lactiplantibacillus plantarum WCFS1. The recombinant strain (WCFS1-trxA) grew better than the control strain (WCFS1-Vector) under acid stress. The expression of thioredoxin system genes was much higher in the recombinant strain compared with the control strain under acid stress. In addition, a series of physiological and biochemical assays were conducted. The ATP content was lower in the recombinant strain, while the cell membrane fluidity and integrity improved in the recombinant strain. Moreover, reactive oxygen species (ROS) accumulation, intracellular GSH level, and superoxide dismutase (SOD) activity assays showed that the recombinant strain decreased the intracellular reactive oxygen species (ROS) accumulation by improving the SOD activity. In conclusion, heterologous expression of trxA improves the SOD activity of L. plantarum WCFS1, reducing bacterial ROS and increasing cell membrane fluidity and integrity, enhancing the tolerance of Lactiplantibacillus plantarum WCFS1 under acid stress.

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.

New Insight into Aspartate Metabolic Pathways in Populus: Linking the Root Responsive Isoenzymes with Amino Acid Biosynthesis during Incompatible Interactions of Fusarium solani

Integrating amino acid metabolic pathways into plant defense and immune systems provides the building block for stress acclimation and host-pathogen interactions. Recent progress in L-aspartate (Asp) and its deployed metabolic pathways highlighted profound roles in plant growth and defense modulation. Nevertheless, much remains unknown concerning the multiple isoenzyme families involved in Asp metabolic pathways in Populus trichocarpa, a model tree species. Here, we present comprehensive features of 11 critical isoenzyme families, representing biological significance in plant development and stress adaptation. The in silico prediction of the molecular and genetic patterns, including phylogenies, genomic structures, and chromosomal distribution, identify 44 putative isoenzymes in the Populus genome. Inspection of the tissue-specific expression demonstrated that approximately 26 isogenes were expressed, predominantly in roots. Based on the transcriptomic atlas in time-course experiments, the dynamic changes of the genes transcript were explored in Populus roots challenged with soil-borne pathogenic Fusarium solani (Fs). Quantitative expression evaluation prompted 12 isoenzyme genes (PtGS2/6, PtGOGAT2/3, PtAspAT2/5/10, PtAS2, PtAspg2, PtAlaAT1, PtAK1, and PtAlaAT4) to show significant induction responding to the Fs infection. Using high-performance liquid chromatography (HPLC) and non-target metabolomics assay, the concurrent perturbation on levels of Asp-related metabolites led to findings of free amino acids and derivatives (e.g., Glutamate, Asp, Asparagine, Alanine, Proline, and α-/γ-aminobutyric acid), showing marked differences. The multi-omics integration of the responsive isoenzymes and differential amino acids examined facilitates Asp as a cross-talk mediator involved in metabolite biosynthesis and defense regulation. Our research provides theoretical clues for the in-depth unveiling of the defense mechanisms underlying the synergistic effect of fine-tuned Asp pathway enzymes and the linked metabolite flux in Populus.

Deficiency of PSRC1 accelerates atherosclerosis by increasing TMAO production via manipulating gut microbiota and flavin monooxygenase 3

Maladaptive inflammatory and immune responses are responsible for intestinal barrier integrity and function dysregulation. Proline/serine-rich coiled-coil protein 1 (PSRC1) critically contributes to the immune system, but direct data on the gut microbiota and the microbial metabolite trimethylamine N-oxide (TMAO) are lacking. Here, we investigated the impact of PSRC1 deletion on TMAO generation and atherosclerosis. We first found that PSRC1 deletion in apoE^-/- mice accelerated atherosclerotic plaque formation, and then the gut microbiota and metabolites were detected using metagenomics and untargeted metabolomics. Our results showed that PSRC1 deficiency enriched trimethylamine (TMA)-producing bacteria and functional potential for TMA synthesis and accordingly enhanced plasma betaine and TMAO production. Furthermore, PSRC1 deficiency resulted in a proinflammatory colonic phenotype that was significantly associated with the dysregulated bacteria. Unexpectedly, hepatic RNA-seq indicated upregulated flavin monooxygenase 3 (FMO3) expression following PSRC1 knockout. Mechanistically, PSRC1 overexpression inhibited FMO3 expression in vitro, while an ERα inhibitor rescued the downregulation. Consistently, PSRC1-knockout mice exhibited higher plasma TMAO levels with a choline-supplemented diet, which was gut microbiota dependent, as evidenced by antibiotic treatment. To investigate the role of dysbiosis induced by PSRC1 deletion in atherogenesis, apoE^-/- mice were transplanted with the fecal microbiota from either apoE^-/- or PSRC1^-/-apoE^-/- donor mice. Mice that received PSRC1-knockout mouse feces showed an elevation in TMAO levels, as well as plaque lipid deposition and macrophage accumulation, which were accompanied by increased plasma lipid levels and impaired hepatic cholesterol transport. Overall, we identified PSRC1 as an atherosclerosis-protective factor, at least in part, attributable to its regulation of TMAO generation via a multistep pathway. Thus, PSRC1 holds great potential for manipulating the gut microbiome and alleviating atherosclerosis.

Integrative multiomics analysis of the acid stress response of Oenococcus oeni mutants at different growth stages

BACKGROUND

Acid stress is one of the most important environmental stresses that adversely affect the growth of lactic acid bacteria (LAB), such as Oenococcus oeni which was isolated from grape-berries and mainly used in wine fermentation. The aim of this paper is to comprehensively characterize the mechanisms of acid stress regulation in O. oeni and to provide a viable theoretical basis for breed and improvement of existing LAB.

METHOD

First, six O. oeni mutants with acid-sensitive (strains b2, a1, c2) and acid-tolerant (strains b1, a3, c1) phenotypes were screened from three wild-type O. oeni, and then their genome (sequencing), transcriptome and metabolome (LC-MS/MS) were examined.

RESULTS

A total of 459 genes were identified with one or more intragenic single nucleotide polymorphisms (SNPs) in these mutants, and were extensively involved in metabolism and cellular functions with a high mutation rates in purine (46%) and pyrimidine (48%) metabolic pathways. There were 210 mutated genes that cause significant changes in expression levels. In addition, 446 differentially accumulated metabolites were detected, and they were consistently detected at relatively high levels in the acid-tolerant O. oeni mutant. The levels of intracellular differentially expressed genes and differential metabolites changed with increasing culture time.

CONCLUSION

The integrative pathways analysis showed that the intracellular response associated with acid regulation differed significantly between acid-sensitive and acid-tolerant O. oeni mutants, and also changed at different growth stages.

Citrulline supplementation attenuates the development of non-alcoholic steatohepatitis in female mice through mechanisms involving intestinal arginase

Non-alcoholic fatty liver disease (NAFLD) is by now the most prevalent liver disease worldwide. The non-proteogenic amino acid l-citrulline (L-Cit) has been shown to protect mice from the development of NAFLD. Here, we aimed to further assess if L-Cit also attenuates the progression of a pre-existing diet-induced NAFLD and to determine molecular mechanisms involved. Female C57BL/6J mice were either fed a liquid fat-, fructose- and cholesterol-rich diet (FFC) or control diet (C) for 8 weeks to induce early stages of NASH followed by 5 more weeks with either FFC-feeding +/- 2.5 g L-Cit/kg bw or C-feeding. In addition, female C57BL/6J mice were either pair-fed a FFC +/- 2.5 g L-Cit/kg bw +/- 0.01 g/kg bw i.p. N(ω)-hydroxy-nor-l-arginine (NOHA) or C diet for 8 weeks.

The protective effects of supplementing L-Cit on the progression of a pre-existing NAFLD were associated with an attenuation of 1) the increased translocation of bacterial endotoxin and 2) the loss of tight junction proteins as well as 3) arginase activity in small intestinal tissue, while no marked changes in intestinal microbiota composition were prevalent in small intestine. Treatment of mice with the arginase inhibitor NOHA abolished the protective effects of L-Cit on diet-induced NAFLD. Our results suggest that the protective effects of L-Cit on the development and progression of NAFLD are related to alterations of intestinal arginase activity and intestinal permeability.

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l-citrulline diminished progression of non-alcoholic fatty liver disease (NAFLD).

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l-citrulline protects from fructose-induced small intestinal barrier dysfunction.

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NASH development is associated with a loss of arginase activity in small intestine.

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l-citrulline improves intestinal arginase activity in diet-induced NAFLD.

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Arginase inhibitor attenuates effects of l-citrulline on NAFLD development.

Characterization of Lactic Acid Bacteria in Raw Buffalo Milk: a Screening for Novel Probiotic Candidates and Their Transcriptional Response to Acid Stress

Lactic acid bacteria (LAB) are important microorganisms for the food industry due to their functional activity, as starters and potential probiotic strains. With that in mind, we explored the LAB diversity in raw buffalo milk, screening for novel potential probiotic strains. A total of 11 strains were identified by combination of MALDI-TOF and partial 16S rDNA sequencing and selected as potential probiotic candidates. Bacteria innocuity assessment was performed by determining antimicrobial susceptibility and the presence of virulence factors. Antagonism activity against Escherichia coli, Pseudomonas aeruginosa, Listeria monocytogenes and Staphylococcus aureus was assessed, as well as milk proteolytic activity and exopolysaccharides production. Seven strains were identified as innocuous and two of them, Lactobacillus rhamnosus LB1.5 and Lactobacillus paracasei LB6.4 were selected for further probiotic potential analyses. Both strains demonstrated adhesion ability to Caco-2 cells, coaggregated with S. aureus and E. coli and maintained cell viability after gastrointestinal simulation in vitro, suggesting their probiotic potential. Furthermore, the transcriptional response of Lact. rhamnosus LB1.5 and Lact. paracasei LB6.4 to in vitro acid stress was assessed by RT-qPCR targeting seven genes related to adhesion, aggregation, stress tolerance, DNA repair and central metabolism. The association between the transcriptional responses and the maintenance of cell viability after gastrointestinal simulation highlights the genetic ability as probiotic of the two selected strains. Finally, we have concluded that Lact. rhamnosus LB1.5 and Lact. paracasei LB6.4 are important probiotic candidates to further in vivo studies.

The local transcriptional regulators SacR1 and SacR2 act as repressors of fructooligosaccharides metabolism in Lactobacillus plantarum

Background

In Lactobacillus plantarum, fructooligosaccharides (FOS) metabolism is controlled by both global and local regulatory mechanisms. Although catabolite control protein A has been identified as a global regulator of FOS metabolism, the functions of local regulators remain unclear. This study aimed to elucidate the roles of two local regulators, SacR1 and SacR2, in the regulation of FOS metabolism in L. plantarum both in vitro and in vivo.

Results

The inactivation of sacR1 and sacR2 affected the growth and production of metabolites for strains grown on FOS or glucose, respectively. A reverse transcription-quantitative PCR analysis of one wild-type and two mutant strains (ΔsacR1 and ΔsacR2) of L. plantarum identified SacR1 and SacR2 as repressors of genes relevant to FOS metabolism in the absence of FOS, and these genes could be induced or derepressed by the addition of FOS. The analysis predicted four potential transcription factor binding sites (TFBSs) in the putative promoter regions of two FOS-related clusters. The binding of SacR1 and SacR2 to these TFBSs both in vitro and in vivo was verified using electrophoretic mobility shift assays and chromatin immunoprecipitation, respectively. A consensus sequence of WNNNNNAACGNNTTNNNNNW was deduced for the TFBSs of SacR1 and SacR2.

Conclusion

Our results identified SacR1 and SacR2 as local repressors for FOS metabolism in L. plantarum. The regulation is achieved by the binding of SacR1 and SacR2 to TFBSs in the promoter regions of FOS-related clusters. The results provide new insights into the complex network regulating oligosaccharide metabolism by lactic acid bacteria.

Petunidin-Based Anthocyanin Relieves Oxygen Stress in Lactobacillus plantarum ST-III

Application of probiotics in the food industry has been hampered by their sensitivity to challenging conditions that reduce their vitality in food matrices. A lot of attempts have been made to promote the growth of these probiotics in the aspect of nutrition demands. Among the other adverse conditions, oxygen stress can restrict the growth of probiotics and has not yet been paid enough attention to. In this study, the effect of a petunidin-based anthocyanin (ACN) on the growth of probiotic Lactobacillus plantarum ST-III was investigated under oxygen stress. The growth of ST-III was analyzed through spot assay on agar plates as well as plating-based enumeration of the viable cells in the liquid culture. Results indicated that ACN could efficiently improve the growth of ST-III under oxygen stress, whereas no effect was observed in the absence of oxygen stress. Further investigations indicated that ACN reduced the oxido-reduction potential of the culture; meanwhile, it exerted a positive transcriptional regulation on the thioredoxin system of ST-III, leading to a decrease in reactive oxygen species accumulation within the cells. Moreover, ACN enabled the growth of ST-III in reconstituted skim milk and promoted the formation of milk clots. These results revealed the role of a petunidin-based ACN in oxygen stress relief and highlighted its potential in manufacture and preservation of L. plantarum-based dairy products.

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.

Comparative Transcriptional Analysis of Lactobacillus plantarum and Its ccpA-Knockout Mutant Under Galactooligosaccharides and Glucose Conditions

Galactooligosaccharides (GOS) are documented prebiotic compounds, but knowledge of the metabolic and regulatory mechanisms of GOS utilization by lactic acid bacteria is still limited. Here we used transcriptome and physiological analyses to investigate the differences in the logarithmic growth phase of Lactobacillus plantarum and L. plantarum ΔccpA metabolizing GOS or glucose as the sole source of carbohydrate. In total, 489 genes (16%) were differentially transcribed in the wild-type L. plantarum grown on glucose and GOS and the value is decreased to 7% due to the loss of ccpA. Only 6% genes were differentially expressed when the wild-type and the ccpA mutant were compared on GOS. Transcriptome data revealed that the carbon sources significantly affected the expression of several genes, and some of the genes were mediated by CcpA. In particular, lac and gal gene clusters resembled the corresponding clusters in L. acidophilus NCFM that are involved in GOS metabolism, indicating that these clusters may be participating in GOS utilization. Moreover, reverse transcription-PCR analysis showed that GOS-related gene clusters were organized in five independent polycistronic units. In addition, many commonalities were found between fructooligosaccharides and GOS metabolism in L. plantarum, including differentially expressed genes involved in oligosaccharide metabolism, conversion of metabolites, and changes in fatty acid biosynthesis. Overall, our findings provide new information on gene transcription and the metabolic mechanism associated with GOS utilization, and confirm that CcpA plays an important role in carbon metabolism regulation in L. plantarum.