[Development and implementation of the course entitled "Virtual Simulation Experiment of Recombinant Human Erythropoietin Manufacturing Process"].

Considering the issues present in traditional learning methods of manufacturing process for biotechnology majors, this paper presents the development and implementation process of the course entitled "Virtual Simulation Experiment of Recombinant Human Erythropoiesis Manufacturing Process". The experiment combines modern biological manufacturing technology and three-dimensional information technology, with recombinant human erythropoiesis drug serving as the focal point. This paper elaborates on the teaching concepts, objectives, contents, implementation methods, experimental procedures, interactive steps, and assessment criteria used in the experiment. Through innovative experimental scheme design, teaching methodologies, and evaluation systems, this course aims to cultivate students' analytical and problem-solving skills in the field of biopharmaceutical engineering, while also broadening students' perspective and expanding their vision.

AcrR1, a novel TetR/AcrR family repressor, mediates acid and antibiotic resistance and nisin biosynthesis in Lactococcus lactis F44.

Lactococcus lactis, widely used in the manufacture of dairy products, encounters various environmental stresses both in natural habitats and during industrial processes. It has evolved intricate machinery of stress sensing and defense to survive harsh stress conditions. Here, we identified a novel TetR/AcrR family transcription regulator, designated AcrR1, to be a repressor for acid and antibiotic tolerance that was derepressed in the presence of vancomycin or under acid stress. The survival rates of acrR1 deletion strain ΔAcrR1 under acid and vancomycin stresses were about 28.7-fold (pH 3.0, HCl), 8.57-fold (pH 4.0, lactic acid) and 2.73-fold (300 ng/mL vancomycin) as that of original strain F44. We also demonstrated that ΔAcrR1 was better able to maintain intracellular pH homeostasis and had a lower affinity to vancomycin. No evident effects of AcrR1 deletion on the growth and morphology of strain F44 were observed. Subsequently, we characterized that the transcription level of genes associated with amino acids biosynthesis, carbohydrate transport and metabolism, multiple drug resistance and DNA repair proteins significantly upregulated in ΔAcrR1 using transcriptome analysis and quantitative reverse transcription-PCR (qRT-PCR) assays. Additionally, AcrR1 could repress the transcription of nisin post-translational modification gene, nisC, leading to a 16.3% increase in nisin yield after AcrR1 deletion. Our results not only refined the knowledge of the regulatory mechanism of TetR/AcrR family regulator in L. lactis, but presented a potential strategy to enhance industrial production of nisin.

Accurate detection of influenza A virus by use of a novel cross-priming isothermal amplification-based point-of-care assay.

Influenza virus is known to cause respiratory tract infections of varying severity in individuals of all ages. The EasyNAT Rapid Flu assay is a newly developed in vitro diagnostic test that employs cross-priming isothermal amplification (CPA) to detect and differentiate influenza A and B viruses in human nasopharyngeal (NP) swabs. The aim of this study is to determine the performance characteristics of the EasyNAT Rapid Flu assay for rapid detection of influenza virus. The limit of detection (LOD) and cross-reactivity of the EasyNAT Rapid Flu assay were assessed. The clinical performance of the assay was evaluated using NP swab samples that were tested with real-time reverse-transcription polymerase chain reaction (RT-PCR) and Xpert Xpress Flu/RSV assay. The LOD for the detection of influenza A and B using the EasyNAT Rapid Flu assay was found to be 500 copies/mL. Furthermore, the assay exhibited no cross-reactivity with other common respiratory viruses tested. For the 114 NP swab samples tested for influenza A using both the EasyNAT Rapid Flu assay and real-time RT-PCR, the two assays demonstrated a high level of agreement (κ = 0.963, P < 0.001), with a positive percentage agreement (PPA) of 97.7% and a negative percentage agreement (NPA) of 98.6%. Similarly, for the 43 NP swab samples tested for influenza A and B using both the EasyNAT Rapid Flu assay and Xpert Xpress Flu/RSV assay, the two assays showed a high level of agreement (κ = 0.933, P < 0.001), with the overall rate of agreement (ORA) of 97.7% for influenza A and 100% for influenza B. The EasyNAT Rapid Flu assay demonstrates excellent performance in the detection of influenza A, highlighted by its strong agreement with RT-PCR-based assays.IMPORTANCEThe newly developed EasyNAT Rapid Flu assay is an innovative cross-priming isothermal amplification-based method designed for detecting influenza A and B viruses at point-of-care settings. This study aims to thoroughly assess the analytical and clinical performance of the assay, offering valuable insights into its potential advantages and limitations. The findings of this research hold significant implications for clinical practice.

Inflammation-associated D-dimer predicts neurological outcome of recent small subcortical infarct: A prospective clinical and laboratory study.

OBJECTIVE: Elevated level of D-Dimer often indicates a worse prognosis in cerebral infarction. However, there is limited research on this impact within recent small subcortical infarction (RSSI). We aim to explore the role of inflammation and the total magnetic resonance imaging (MRI) burden of cerebral small vessel disease (cSVD) in this process. METHODS: 384 RSSI patients and 189 matched healthy controls were strictly registered in the current research. We evaluated short-term and long-term outcomes by measuring the percentage of the National Institutes of Health Stroke Scale (NIHSS) improvement and the modified Rankin Scale (mRS) at 3 months, respectively. We also assessed the chronic, sustained brain damage associated with cSVD using the total MRI burden and confirmed the relationship between prognosis and the total MRI burden of cSVD. Furthermore, we explored the associations between D-dimer and C-reactive protein (CRP) levels with NIHSS improvement and mRS at 3 months, as well as their relationships with both the total MRI burden of cSVD and its 4 imaging features. RESULTS: Both NIHSS improvement and the mRS at 3 months were found to be correlated with the total MRI burden of cSVD. Higher D-dimer and CRP levels showed a linear correlation, indicating worse prognosis and a higher total MRI burden of cSVD. The four imaging features of the total MRI burden of cSVD did not exhibit entirely consistent patterns when exploring their correlations with prognosis and laboratory indicators. CONCLUSION: Inflammation-associated D-dimer predicts neurological outcomes in patients with recent small subcortical infarct, and reflects a more severe total MRI burden of cSVD.

Enzyme and Metabolic Engineering Strategies for Biosynthesis of α-Farnesene in Saccharomyces cerevisiae.

α-Farnesene, a type of acyclic sesquiterpene, is an important raw material in agriculture, aircraft fuel, and the chemical industry. In this study, we constructed an efficient α-farnesene-producing yeast cell factory by combining enzyme and metabolic engineering strategies. First, we screened different plants for α-farnesene synthase (AFS) with the best activity and found that AFS from Camellia sinensis (CsAFS) exhibited the most efficient α-farnesene production in Saccharomyces cerevisiae 4741. Second, the metabolic flux of the mevalonate pathway was increased to improve the supply of the precursor farnesyl pyrophosphate. Third, inducing site-directed mutagenesis in CsAFS, the CsAFSW281C variant was obtained, which considerably increased α-farnesene production. Fourth, the N-terminal serine-lysine-isoleucine-lysine (SKIK) tag was introduced to construct the SKIK∼CsAFSW281C variant, which further increased α-farnesene production to 2.8 g/L in shake-flask cultures. Finally, the α-farnesene titer of 28.3 g/L in S. cerevisiae was obtained by fed-batch fermentation in a 5 L bioreactor.

Detection of emerging HoBi-like Pestivirus (BVD-3) during an epidemiological investigation of bovine viral diarrhea virus in Xinjiang: a first-of-its-kind report.

Xinjiang pastoral area is the second largest pastoral area in China, accounting for 26.8% of the available grassland area in the country, and the geographical advantage of cattle breeding industry is very obvious. Bovine viral diarrhea virus (BVDV) has always been one of the important viral diseases that have plagued the development of cattle farming industry in the world. As one of the main pastoral areas of China's cattle farming industry, the Xinjiang pastoral area has also been deeply affected. In this study, 6,153 bovine serum samples were collected from 18 large-scale cattle farms in 13 cities in Xinjiang. The antibodies and antigens of 6,153 and 588 serum samples were detected by serological detection methods, respectively. Ten serum samples, which were antigen-positive by ELISA, were randomly selected for RT-PCR detection, sequencing, and phylogenetic analysis of suspected HoBi-like Pestivirus (HoBiPeV) strains. The results showed that the positive rates of BVDV antibodies and antigens were 53.68% (3,303/6,153) and 6.12% (36/588), respectively. One of the 10 randomly selected seropositive samples was infected with the HoBiPeV strain. HoBiPeV, also referred to as BVDV-3, is an emerging atypical Pestivirus that occurs in cattle and small ruminants, and its clinical signs are similar to those of BVDV infection. Based on the whole genome of the BVDV-3 reference strain (JS12/01) on the GenBank, the homology of the detected strain was 96.02%. The whole genome nucleotide sequence was submitted to the GenBank database, and the gene accession number was obtained: OP210314. The whole genome of isolate OP210314 was 12.239 nucleotides and contained a 5'-UTR of 340 nucleotides, a 3'-UTR of 199 nucleotides, and a large open reading frame (ORF) encoding a polyprotein consisting of 3,899 amino acids. In conclusion, the prevalence rate of BVDV infection in Xinjiang dairy cows is high, and the genetic diversity is increasing. This study successfully identified and isolated HoBiPeV in Xinjiang for the first time, posing a potential threat to the cattle industry in Xinjiang.

Elevated serum levels of human epididymis protein 4 in adult patients with proliferative lupus nephritis.

Background: This study aimed to access whether serum human epididymis protein 4 (HE4) level could identify lupus nephritis (LN) pathological classes in adults and children. Methods: The serum HE4 levels of 190 healthy subjects and 182 patients with systemic lupus erythematosus (SLE) (61 adult-onset LN [aLN], 39 childhood-onset LN [cLN], and 82 SLE without LN) were determined using Architect HE4 kits and an Abbott ARCHITECT i2000SR Immunoassay Analyzer. Results: Serum HE4 level was significantly higher in the aLN patients (median, 85.5 pmol/L) than in the patients with cLN (44 pmol/L, P < 0.001) or SLE without LN (37 pmol/L, P < 0.001), or the healthy controls (30 pmol/L, P < 0.001). Multivariate analysis showed that serum HE4 level was independently associated with aLN. Stratified by LN class, serum HE4 level was significantly higher in the patients with proliferative LN (PLN) than in those with non-PLN, and this difference was found only in aLN (median, 98.3 versus 49.3 pmol/L, P = 0.021) but not in cLN. Stratified by activity (A) and chronicity (C) indices, the aLN patients with class IV (A/C) possessed significantly higher serum HE4 levels than those with class IV (A) (median, 195.5 versus 60.8 pmol/L, P = 0.006), and this difference was not seen in the class III aLN or cLN patients. Conclusion: Serum HE4 level is elevated in patients with class IV (A/C) aLN. The role of HE4 in the pathogenesis of chronic lesions of class IV aLN needs further investigation.

LssR plays a positive regulatory role in acid and nisin tolerance response of Lactococcus lactis.

In Lactococcus lactis, different regulation mechanisms can be activated to overcome the effects of adverse environmental stresses. Here, a TetR family regulator LssR was demonstrated as a positive regulator in the activation of the mechanisms involved in acid and nisin tolerance of L. lactis. The deletion of lssR led to the reduction of tolerance of L. lactis NZ9000 to nisin and acid stress, and the survival rates of NZ9000 under nisin and acid stress were roughly 20-fold, 10-fold (pH 3.0, hydrochloric acid), and 8.9-fold (pH 4.0, lactic acid) of the lssR mutant NZΔlssR, respectively. Moreover, the lssR mutant NZΔlssR also displayed a lower intracellular pH stability and a changed cell surface morphology. Subsequently, transcriptome analysis revealed that genes related to the arginine deiminase pathway, the surface polysaccharides biosynthesis, carbohydrates transport and metabolism, multidrug resistance, cell repair proteins and chaperones were predominantly down transcribed in NZΔlssR. The transcript levels of the arginine deiminase pathway and the surface polysaccharides biosynthesis-associated genes under acid and nisin stresses were compared between the wild type NZ9000 and NZΔlssR using real-time fluorescence quantitative PCR. It revealed that the arginine deiminase pathway genes (arcD1C1C2T) and the surface polysaccharides biosynthesis genes (cgT, gmhB, gmhA, hddA, tagH and tarS) were proposed to be the main regulatory mechanisms of LssR in response to the acid and nisin stresses. Overall, the important role of LssR in the acid and nisin stresses response was demonstrated and the putative regulation mechanism of LssR was revealed.

Combinational quorum sensing devices for dynamic control in cross-feeding cocultivation.

Quorum sensing (QS) offers cell density dependent dynamic regulations in cell culture through devices such as synchronized lysis circuit (SLC) and metabolic toggle switch (MTS). However, there is still a lack of studies on cocultivation with a combination of different QS-based devices. Taking the production of isopropanol and salidroside as case studies, we have mathematically modeled a comprehensive set of QS-regulated cocultivation schemes and constructed experimental combinations of QS devices, respectively, to evaluate their feasibility and optimality for regulating growth competition and corporative production. Glucose split ratio is proposed for the analysis of competition between cell growth and targeted production. Results show that the combination of different QS devices across multiple members offers a new tool with the potential to effectively coordinate synthetic microbial consortia for achieving high product titer in cross-feeding cocultivation. It is also evident that the performance of such systems is significantly affected by dynamic characteristics of chosen QS devices, carbon source control and the operational settings. This study offers insights for future applications of combinational QS devices in synthetic microbial consortia.

The rfbN gene of Salmonella Typhimurium mediates phage adsorption by modulating biosynthesis of lipopolysaccharide.

The study of the interaction mechanism between bacteriophage and host is helpful in promoting development of bacteriophage applications. The mechanism of the interaction with the phage was studied by constructing the rfbN gene deletion and complemented with strains of Salmonella enterica subspecies enterica serovar Typhimurium (Salmonella Typhimurium, S. Typhimurium) D6. The rfbN gene deletion strain could not be lysed by phage S55 and led to a disorder of lipopolysaccharide (LPS) biosynthesis, which changed from the smooth type to rough type. Also, the RfbN protein lacking any of the three-segment amino acid (aa) sequences (90-120 aa, 121-158 aa, and 159-194 aa) produces the same result. Transmission electron microscopy and confocal microscopy assays demonstrated that phage S55 dramatically reduced adsorption to the rfbN deletion strain as compared to the wild strain D6. After co-incubation of the S55 with the purified smooth LPS, D6 could not be lysed, indicating that the smooth LPS binds to the S55 in vitro and then inhibits the cleavage activity of the S55. To sum up, the rfbN gene affects phage adsorption by regulating LPS synthesis. Furthermore, the functioning of the RfbN protein requires the involvement of multiple structures. To the best of our knowledge, this study is the first report of the involvement of the bacterial rfbN gene involved in the phage-adsorption process.

Analysis of Nonlinear Transient Energy Effect on Thermoelectric Energy Storage Structure.

In complex flight conditions, due to the large amount of unusable heat generated by aerodynamic heating, the thermal protection system of an aircraft needs to withstand a large temperature shock, which brings great challenges to the design of the structure. In order to effectively utilize the irregular aerodynamic heat, and improve structural heat conduction, a composite structure is formed by using phase change energy storage materials on the basis of the thermoelectric structure, which transforms the aerodynamic waste heat into stable electric energy for the internal system. Through the study of the response of nonlinear transient energy, it is found that the thermoelectric and mechanical properties of the new structure can be improved by adding phase change energy storage materials. Under actual flight conditions, the new structure can reduce the maximum temperature by 180 K and the maximum thermal stress by 110 Mpa. The mechanical properties of the structure are effectively improved, the service life of the structure is prolonged, and the waste heat can be converted into stable electrical energy output to improve the thermoelectric output performance. On the premise of ensuring conversion efficiency, the output power of the new structure has been improved by 64.8% through structural optimization under actual flight conditions.

NisI Maturation and Its Influence on Nisin Resistance in Lactococcus lactis.

NisI confers immunity against nisin, with high substrate specificity to prevent a suicidal effect in nisin-producing Lactococcus lactis strains. However, the NisI maturation process as well as its influence on nisin resistance has not been characterized. Here, we report the roles of lipoprotein signal peptidase II (Lsp) and prolipoprotein diacylglyceryl transferase (Lgt) in NisI maturation and nisin resistance of L. lactis F44. We found that the resistance of nisin of an Lsp-deficient mutant remarkably decreased, while no significant differences in growth were observed. We demonstrated that Lsp could cleave signal peptide of NisI precursor in vitro Moreover, diacylglyceryl modification of NisI catalyzed by Lgt played a decisive role in attachment of NisI on the cell envelope, while it exhibited no effects on cleavage of the signal peptides of NisI precursor. The dissociation constant (KD ) for the interaction between nisin and NisI exhibited a 2.8-fold increase compared with that between nisin and pre-NisI with signal peptide by surface plasmon resonance (SPR) analysis, providing evidence that Lsp-catalyzed signal peptide cleavage was critical for the immune activity of NisI. Our study revealed the process of NisI maturation in L. lactis and presented a potential strategy to enhance industrial nisin production.IMPORTANCE Nisin, a safe and natural antimicrobial peptide, has a long and impressive history as a food preservative and is also considered a novel candidate to alleviate the increasingly serious threat of antibiotic resistance. Nisin is produced by certain L. lactis strains. The nisin immunity protein NisI, a membrane-bound lipoprotein, is expressed by nisin producers to avoid suicidal action. Here, we report the roles of Lsp and Lgt in NisI maturation and nisin resistance of L. lactis F44. The results verified the importance of Lsp to NisI-conferred immunity and Lgt to localization. Our study revealed the process of NisI maturation in L. lactis and presented a potential strategy to enhance industrial nisin production.

[Research Progress on New Drug Therapy for Primary Immune Thrombocytopenic Purpura in Adults--Review].

Immune thrombocytopenia (ITP) is an immune disease characterized by an increased risk of hemorrhagic disease caused by a decrease in platelet count. At present, the first line, second-line treatment can not completely or maintain continuous remission of ITP. New treatments in recent research include stimulating platelet-producing drugs, Syk inhibitors, and molecular-targeted drugs, etc., which can play a role in key steps of the progression of the disease. Among them, new types of drugs that stimulate thrombopoiesis shows a better therapeutic prospects with a comparative mechanism and clinical research, Syk inhibitors have a unique role in the treatment of malignant diseases in blood system, and the transplantation of mesenchymal stem cells is a new treatment idea. These treatments show the potential to improve the quality of life in patients with ITP. In this review, the latest research progress of new therapeutic drugs for ITP is summarized briefly.

Co-production of Nisin and γ-Aminobutyric Acid by Engineered Lactococcus lactis for Potential Application in Food Preservation.

Microbiological contamination and oxidative damage are the two main challenges in maintaining quality and improving shelf-life of foods. Here, we developed a Lactococcus lactis fermentation system that could simultaneously produce nisin, an antimicrobial peptide, and γ-aminobutyric acid (GABA), an antioxidant agent. In this system, we metabolically engineered a nisin producing strain L. lactis F44 for GABA production by expression of glutamate decarboxylase and glutamate/GABA antiporter. GABA biosynthesis could facilitate nisin production through enhancing acid resistance of the strain. By applying a two-stage pH-control fermentation strategy, the engineered strain yielded up to 9.12 g/L GABA, which was 2.2 times higher than that of pH-constant fermentation. Furthermore, we demonstrated the potential application of the freeze-dried fermentation product as a preservative to improve the storage performance of meat and fruit. These results suggested that the fermentation product of nisin-GABA co-producing strain could serve as a cost-effective, easily prepared, and high-performance food preservative.

Two-stage carbon distribution and cofactor generation for improving l-threonine production of Escherichia coli.

L-Threonine, a kind of essential amino acid, has numerous applications in food, pharmaceutical, and aquaculture industries. Fermentative l-threonine production from glucose has been achieved in Escherichia coli. However, there are still several limiting factors hindering further improvement of l-threonine productivity, such as the conflict between cell growth and production, byproduct accumulation, and insufficient availability of cofactors (adenosine triphosphate, NADH, and NADPH). Here, a metabolic modification strategy of two-stage carbon distribution and cofactor generation was proposed to address the above challenges in E. coli THRD, an l-threonine producing strain. The glycolytic fluxes towards tricarboxylic acid cycle were increased in growth stage through heterologous expression of pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and citrate synthase, leading to improved glucose utilization and growth performance. In the production stage, the carbon flux was redirected into l-threonine synthetic pathway via a synthetic genetic circuit. Meanwhile, to sustain the transaminase reaction for l-threonine production, we developed an l-glutamate and NADPH generation system through overexpression of glutamate dehydrogenase, formate dehydrogenase, and pyridine nucleotide transhydrogenase. This strategy not only exhibited 2.02- and 1.21-fold increase in l-threonine production in shake flask and bioreactor fermentation, respectively, but had potential to be applied in the production of many other desired oxaloacetate derivatives, especially those involving cofactor reactions.

A novel small RNA S042 increases acid tolerance in Lactococcus lactis F44.

Lactococcus lactis, a gram-positive bacterium, encounters various environmental stresses, especially acid stress, during fermentation. Small RNAs (sRNAs) that serve as regulators at post-transcriptional level play important roles in acid stress response. Here, a novel sRNA S042 was identified by RNA-Seq, RT-PCR and Northern blot. The transcription level of s042 was upregulated 2.29-fold under acid stress by Quantitative RT-PCR (qRT-PCR) analysis. Acid tolerance assay showed that overexpressing s042 increased the survival rate of L. lactis F44 and deleting s042 significantly inhibited the viability under acidic conditions. Moreover, the targets were predicted by online software and four genes were chosen as candidates. Among them, argR (arginine regulator) and accD (acetyl-CoA carboxylase carboxyl transferase subunit beta) were validated to be the direct targets activated by S042 through reporter fusion assay. The regulatory mechanism between S042 and its targets was further investigated through Bioinformatics and qRT-PCR. This study served to highlight the role of the novel sRNA S042 in acid resistance of L. lactis and provided new insights into the response mechanism of acid stress.

Preparation, characterization and antioxidant activity of polysaccharide from spent Lentinus edodes substrate.

This study explored the potential of spent Lentinus edodes substrate, a by-product of mushroom industries causing environmental pollution, serving as materials to produce antioxidant polysaccharide. The extraction process of spent Lentinus edodes substrate polysaccharide (SLSP) was optimized and the effects of drying methods on chemical composition, morphological property and antioxidant activity were investigated. Results showed that freeze-dried SLSP (SLSP-F) exhibited the best quality in terms of the polysaccharide yield (13.00%) and antioxidant activity. The EC50 values of SLSP-F on DPPH, ABTS and superoxide anion radicals was 0.051mg/mL, 0.379mg/mL, 0.719mg/mL, respectively, which was significantly lower than that of freeze-dried Lentinus edodes polysaccharide (LP-F). After purification by Sephadex G-150, the purified SLSP-F (PSP) has a molecular weight of 16.77kDa. Compared with LP-F, PSP has more reducing sugars and uronic acids in chemical composition and higher contents of xylose, glucose and galactose in monosaccharide composition. FT-IR and NMR spectroscopy analysis revealed that PSP has both α and ß glycosidic bonds and massive acetyl groups, which is different from LP-F mainly composed of 1, 3 linked α-D-Manp residue with some acetyl groups. The findings provided a reliable approach for the development of antioxidant polysaccharide from spent Lentinus edodes substrate.

Contribution of YthA, a PspC Family Transcriptional Regulator of Lactococcus lactis F44 Acid Tolerance and Nisin Yield: a Transcriptomic Approach.

To overcome the adverse impacts of environmental stresses during growth, different adaptive regulation mechanisms can be activated in Lactococcus lactis In this study, the transcription levels of eight transcriptional regulators of L. lactis subsp. lactis F44 under acid stress were analyzed using quantitative reverse transcription-PCR. Eight gene-overexpressing strains were then constructed to examine their influences on acid-resistant capability. Overexpressing ythA, a PspC family transcriptional regulator, increased the survival rate by 3.2-fold compared to the control at the lethal pH 3.0 acid shock. Moreover, the nisin yield was increased by 45.50%. The ythA-overexpressing strain FythA appeared to have higher intracellular pH stability and nisin-resistant ability. Subsequently, transcriptome analysis revealed that the vast majority of genes associated with amino acid biosynthesis, including arginine, serine, phenylalanine, and tyrosine, were predominantly upregulated in FythA. Arginine biosynthesis (argG and argH), arginine deiminase pathway, and polar amino acid transport (ysfE and ysfF) were proposed to be the main regulation mechanisms of YthA. Furthermore, the transcription of genes associated with pyrimidine and exopolysaccharide biosynthesis were upregulated. The transcriptional levels of nisIPRKFEG genes were substantially higher in FythA, which directly contributed to the yield and resistance of nisin. Three potential DNA-binding sequences were predicted by computer analysis using the upstream regions of genes with prominent changes. This study showed that YthA could increase acid resistance and nisin yield and revealed a putative regulation mechanism of YthA.IMPORTANCE Nisin, produced by Lactococcus lactis subsp. lactis, is widely used as a safe food preservative. Acid stress becomes the primary restrictive factor of cell growth and nisin yield. In this research, we found that the transcriptional regulator YthA was conducive to enhancing the acid resistance of L. lactis F44. Overexpressing ythA could significantly improve the survival rate and nisin yield. The stability of intracellular pH and nisin resistance were also increased. Transcriptome analysis showed that nisin immunity and the biosynthesis of some amino acids, pyrimidine, and exopolysaccharides were enhanced in the engineered strain. This study elucidates the regulation mechanism of YthA and provides a novel strategy for constructing robust industrial L. lactis strains.

Improving nitrogen source utilization from defatted soybean meal for nisin production by enhancing proteolytic function of Lactococcus lactis F44.

Nisin, one kind of natural antimicrobial peptide, is produced by certain Lactococcus lactis strains, which generally require expensive high-quality nitrogen sources due to limited ability of amino acids biosynthesis. Here we use defatted soybean meal (DSM) as sole nitrogen source to support L. lactis growth and nisin production. DSM medium composition and fermentation conditions were optimized using the methods of Plackett-Burman design and central composite design. The highest nisin production of 3879.58 IU/ml was obtained in DSM medium, which was 21.3% higher than that of commercial medium. To further increase the utilization ability of nitrogen sources, we enhanced the proteolytic function in L. lactis through rationally expressing the related enzymes, which were selected according to the compositions of amino acids and molecular weight of peptides in DSM medium. Significantly, an artificial proteolytic system consisting of a heterologous protease (NprB), an oligopeptides transporter subunit (OppA) and two peptidases (PepF and PepM) was introduced into L.lactis. The constructed strain BAFM was capable of achieving efficient biomass accumulation and nisin yield with 30% decreased amount of DSM hydrolysates, which further reduced the cost of nisin production. The strategy described here offers opportunities for low-cost L. lactis fermentation and large-scale nisin production in industry.

Promoting acid resistance and nisin yield of Lactococcus lactis F44 by genetically increasing D-Asp amidation level inside cell wall.

Nisin fermentation by Lactococcus lactis requires a low pH to maintain a relatively higher nisin activity. However, the acidic environment will result in cell arrest, and eventually decrease the relative nisin production. Hence, constructing an acid-resistant L. lactis is crucial for nisin harvest in acidic nisin fermentation. In this paper, the first discovery of the relationship between D-Asp amidation-associated gene (asnH) and acid resistance was reported. Overexpression of asnH in L. lactis F44 (F44A) resulted in a sevenfold increase in survival capacity during acid shift (pH 3) and enhanced nisin desorption capacity compared to F44 (wild type), which subsequently contributed to higher nisin production, reaching 5346 IU/mL, 57.0% more than that of F44 in the fed-batch fermentation. Furthermore, the engineered F44A showed a moderate increase in D-Asp amidation level (from 82 to 92%) compared to F44. The concomitant decrease of the negative charge inside the cell wall was detected by a newly developed method based on the nisin adsorption amount onto cell surface. Meanwhile, peptidoglycan cross-linkage increased from 36.8% (F44) to 41.9% (F44A), and intracellular pH can be better maintained by blocking extracellular H+ due to the maintenance of peptidoglycan integrity, which probably resulted from the action of inhibiting hydrolases activity. The inference was further supported by the acmC-overexpression strain F44C, which was characterized by uncontrolled peptidoglycan hydrolase activity. Our results provided a novel strategy for enhancing nisin yield through cell wall remodeling, which contributed to both continuous nisin synthesis and less nisin adsorption in acidic fermentation (dual enhancement).