Search

BACKGROUND: Streptococcus thermophilus is an important strain widely used in dairy fermentation, with distinct urea metabolism characteristics compared to other lactic acid bacteria. The conversion of urea by S. thermophilus has been shown to affect the flavor and acidification characteristics of milk. Additionally, urea metabolism has been found to significantly increase the number of cells and reduce cell damage under acidic pH conditions, resulting in higher activity. However, the physiological role of urea metabolism in S. thermophilus has not been fully evaluated. A deep understanding of this metabolic feature is of great significance for its production and application. Genome‐scale metabolic network models (GEMs) are effective tools for investigating the metabolic network of organisms using computational biology methods. Constructing an organism‐specific GEM can assist us in comprehending its characteristic metabolism at a systemic level. RESULTS: In the present study, we reconstructed a high‐quality GEM of S. thermophilus S‐3 (iCH492), which contains 492 genes, 608 metabolites and 642 reactions. Growth phenotyping experiments were employed to validate the model both qualitatively and quantitatively, yielding satisfactory predictive accuracy (95.83%), sensitivity (93.33%) and specificity (100%). Subsequently, a systematic evaluation of urea metabolism in S. thermophilus was performed using iCH492. The results showed that urea metabolism reduces intracellular hydrogen ions and creates membrane potential by producing and transporting ammonium ions. This activation of glycolytic fluxes and ATP synthase produces more ATP for biomass synthesis. The regulation of fluxes of reactions involving NAD(P)H by urea metabolism improves redox balance. CONCLUSION: Model iCH492 represents the most comprehensive knowledge‐base of S. thermophilus to date, serving as a potent tool. The evaluation of urea metabolism led to novel insights regarding the role of urease. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

BACKGROUND: The two essential editing elements in the clustered regularly interspaced short palindromic repeats (CRISPR) editing system are promoter and single‐guide RNA (sgRNA), the latter of which determines whether Cas protein can precisely target a specific location to edit the targeted gene. Therefore, the selection of sgRNA is crucial to the efficiency of the CRISPR editing system. Various online prediction tools for sgRNA are currently available. These tools can predict all possible sgRNAs of the targeted gene and rank sgRNAs according to certain scoring criteria according to the demands of the user. RESULTS: We designed sgRNAs for Lactococcus lactis NZ9000 LLNZ_RS02020 (ldh) and LLNZ_RS10925 (upp) individually using online prediction software – CRISPOR – and successfully constructed a series of knockout strains to allow comparison of the knockout efficiency of each sgRNA and analyze the differences between software predictions and actual experimental results. CONCLUSION: Our experimental results showed that the actual editing efficiency of the screened sgRNAs did not match the predicted results – a phenomenon that suggests that established findings from eukaryotic studies are not universally applicable to prokaryotes. Software prediction can still be used as a tool for the initial screening of sgRNAs before further selection of suitable sgRNAs through experimental experience. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

BACKGROUND: It has been well accepted that lactic acid bacteria (LAB) are the main bacterial genera present during the brewing of Chinese rice wine (CRW). LAB plays a decisive role in the flavor quality of CRW; however, its application in CRW has previously been overlooked. Therefore, effects of different LAB as co‐fermenter on the flavor characteristics of CRW were investigated. RESULTS: Co‐fermentation of LAB increased the utilization rate of reducing sugar, concentration of lactic acid, amino acid nitrogen and total acidity, as well as the content of volatile flavor compounds. Different LAB doses had little effect on the flavor profiles of CRW, but the species of LAB greatly affected the flavor characteristic. The flavor of CRW co‐fermented with Lactococcus lactis was characterized by long‐chain fatty acid ethyl esters, while co‐fermentation with Weissella confusa highlighted the ethyl esters of low molecular weight and short carbon chains in the resultant CRW. Alcohol compounds were dominant in the CRW co‐fermented using Pediococcus pentosaceus. CONCLUSION: The co‐fermentation of LAB increased the number of volatile flavor compounds, especially esters. LAB exhibited great potential in the application of CRW industry to enrich the flavor characteristics and enhance the flavor diversity of the final product. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

This paper investigates system identification algorithms for modal identification of frame structures, such as a suspension bridge and an overhead transmission line-crossing frame, using ambient vibration measurements. The modal identification procedures include two novel blind source separation (BSS) algorithms, complexity pursuit method (CP) and generalized eigen decomposition method (GED), based on modern signal processing technology. Here, the frequency response function (FRF) method is introduced as an important reference to verify the effectiveness of the CP algorithm and GED algorithm. The effectiveness and accuracy of both types of algorithms are verified by numerical simulations and experiments on a suspension bridge. In addition, an engineering application of these two BSS methods is successfully implemented in an overhead transmission line-crossing frame. The results show that the two novel BSS learning rules (CP and GED) are capable of successfully identifying modal parameters of the civil structure under ambient excitation. [ABSTRACT FROM AUTHOR]

BACKGROUND: Probiotic lactic acid bacterium Lactiplantibacillus plantarum is widely used in the dairy and other fermented food industries. L. plantarum AR113 harbors a C30 carotenoid operon crtNM based on genomic analysis, but the yield of C30 carotenoid is only 8.1 μg g‐1 DCW. RESULTS: To improve the productivity of C30 carotenoid, crtNM from L. plantarum AR113 was cloned and reconstructed in Escherichia coli BL21(DE3). The proteins crtN and crtM were successfully expressed based on a sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS‐PAGE) analysis, and the carotenoid was detected using high‐performance liquid chromatography (HPLC) and liquid chromatography–mass spectrometry (LC–MS). In comparison with the constitutive promoter P44, the use of the inducible T7 promoter significantly increased the carotenoid content in E. coli. The fermentation conditions were also optimized with induction by 0.5 mmol/L IPTG at 20 °C for 7 h. The yield of C30 carotenoid reached 154.5 μg g‐1 DCW, which was 18‐fold higher than that of L. plantarum AR113. The 2,2‐diphenyl‐1‐picryl (DPPH) and 2,2′‐azino‐bis (3‐ethylbenzothiazoline‐6sulfonic acid (ABTS) radical scavenging capacity of C30 carotenoids synthesized by heterologous expression in E. coli was also higher than that of the antioxidant food additive butylated hydroxytoluene. CONCLUSIONS: Our findings suggest that E. coli has strong potential as a basic chassis for the production of C30 carotenoids from Lactiplantibacillus with high antioxidant activity. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]