Enhancement of recombinant streptokinase production in Lactococcus lactis by suppression of acid tolerance response

Characterization of a Panel of Constitutive Promoters from Lactococcus cremoris for Fine-Tuning Gene Expression

Lactococcus cremoris (homotypic synonym: Lactococcus lactis) is receiving increasing attention as a prominent vehicle for the delivery of live vaccines. This can hardly be achieved without developing tools for the genetic manipulation of L. cremoris, and the paucity of studies on L. cremoris endogenous promoters has attracted our attention. Here, we report the discovery and characterization of 29 candidate promoters identified from L. cremoris subsp. cremoris NZ9000 by RNA sequencing analysis. Furthermore, 18 possible constitutive promoters were obtained by RT-qPCR screening from these 29 candidate promoters. Then, these 18 promoters were cloned and characterized by a reporter gene, gusA, encoding β-glucuronidase. Eventually, eight endogenous constitutive promoters of L. cremoris were obtained, which can be applied to genetic manipulation of lactic acid bacteria.

Expression of β-Glucosidases from the Yak Rumen in Lactic Acid Bacteria: A Genetic Engineering Approach

β-glucosidase derived from microorganisms has wide industrial applications. In order to generate genetically engineered bacteria with high-efficiency β-glucosidase, in this study two subunits (bglA and bglB) of β-glucosidase obtained from the yak rumen were expressed as independent proteins and fused proteins in lactic acid bacteria (Lactobacillus lactis NZ9000). The engineered strains L. lactis NZ9000/pMG36e-usp45-bglA, L. lactis NZ9000/pMG36e-usp45-bglB, and L. lactis NZ9000/pMG36e-usp45-bglA-usp45-bglB were successfully constructed. These bacteria showed the secretory expression of BglA, BglB, and Bgl, respectively. The molecular weights of BglA, BglB, and Bgl were about 55 kDa, 55 kDa, and 75 kDa, respectively. The enzyme activity of Bgl was significantly higher (p < 0.05) than that of BglA and BglB for substrates such as regenerated amorphous cellulose (RAC), sodium carboxymethyl cellulose (CMC-Na), desiccated cotton, microcrystalline cellulose, filter paper, and 1% salicin. Moreover, 1% salicin appeared to be the most suitable substrate for these three recombinant proteins. The optimum reaction temperatures and pH values for these three recombinant enzymes were 50 °C and 7.0, respectively. In subsequent studies using 1% salicin as the substrate, the enzymatic activities of BglA, BglB, and Bgl were found to be 2.09 U/mL, 2.36 U/mL, and 9.4 U/mL, respectively. The enzyme kinetic parameters (Vmax, Km, Kcat, and Kcat/Km) of the three recombinant strains were analyzed using 1% salicin as the substrate at 50 °C and pH 7.0, respectively. Under conditions of increased K⁺ and Fe²⁺ concentrations, the Bgl enzyme activity was significantly higher (p < 0.05) than the BglA and BglB enzyme activity. However, under conditions of increased Zn²⁺, Hg²⁺, and Tween20 concentrations, the Bgl enzyme activity was significantly lower (p < 0.05) than the BglA and BglB enzyme activity. Overall, the engineered lactic acid bacteria strains generated in this study could efficiently hydrolyze cellulose, laying the foundation for the industrial application of β-glucosidase.

Nitrogen supplementation ameliorates product quality and quantity during high cell density bioreactor studies of Pichia pastoris: A case study with proteolysis prone streptokinase

Streptokinase is a well-established cost-effective therapeutic molecule for thrombo-embolic complications. In the current study, a tag-free variant of streptokinase with a native N-terminus (N-rSK) was developed using the Pichia expression system. A three-copy clone was screened that secreted 1062 mg/L of N-rSK in the complex medium at shake flask level. The biologically active (67,552.61 IU/mg) N-rSK recovered by anion exchange chromatography was predicted to contain 15.43% α-helices, 26.43% β-sheets. The fermentation run in a complex medium yielded a poor quality product due to excessive N-rSK degradation. Therefore, modified basal salt medium was also employed during fermentation operations to reduce the proteolytic processing of the recombinant product. The concomitant feeding of 1 g/L/h soya flour hydrolysate with methanol during the protein synthesis phase reduced the proteolysis and yielded 2.29 g/L of N-rSK. The fermentation medium was also supplemented with urea during growth and induction phases. The combined feeding approach of nitrogen-rich soya flour hydrolysate and urea during bioreactor operations showed significant improvement in protein stability and resulted in a 4-fold increase in N-rSK concentration to a level of 4.03 g/L over shake flask. Under optimized conditions, the volumetric productivity and specific product yield were 52.33 mg/L/h and 33.24 mg/g DCW, respectively.

Expression of Helicobacter pylori CagL gene in Lactococcus lactis MG1363 and evaluation of its immunogenicity as an oral vaccine in mice

Helicobacter pylori is a gram negative pathogen which commonly colonizes in the human gastric mucosa from early childhood and persists throughout life. CagL is a 27-kDa protein that is located at the tip of T4SS pili and highly conserved among pathogenic H. pylori strains. Lactic acid bacteria especially Lactococcus lactis (L. lactis) could serve as an antigen-delivering vehicle for the development of edible vaccine. In this study H. pylori CagL gene was cloned in pAMJ2008 vector and transferred to Lactococcus lactis MG1363 as the host for CagL antigen production. This recombinant bacterium was orally subjected to mice, and the immune response to CagL was evaluated by ELISA. Intracellular expression of CagL protein was confirmed by Western blot analysis. Mucosal immunization of mice with the recombinant L. lactis significantly stimulated CagL-Specific antibodies: IgA, IgG, cytokine IL-17 and IFN-γ. Moreover, the specific anti-CagL IgA response was detected in the feces of immunized mice. These results indicate that CagL of H. pylori was successfully expressed in L. lactis and the recombinant bacteria can be potentially used as an edible vaccine against H. pylori infection.

Secretion of tumoricidal human tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) by recombinant Lactococcus lactis: optimization of in vitro synthesis conditions

BACKGROUND

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively eliminates tumor cells. However, the short biological half-life of this molecule limits its potential use in the clinic. Our aim was to construct a recombinant strain of nonpathogenic Lactococcus lactis bacteria as a vector for effective and prolonged human TRAIL production. Herein, we examined the expression and secretion conditions leading to the production of biologically active protein in vitro.

RESULTS

The human soluble TRAIL-cDNA (hsTRAIL-cDNA) with optimized codons was designed to fit the codon usage pattern (codon bias) of the L. lactis host. This cDNA construct was synthesized and cloned in lactococcal plasmid secretion vector pNZ8124 under the control of the nisin-induced PnisA promoter. The pNZ8124-hsTRAIL plasmid vector was transformed into the L. lactis NZ9000 host strain cells by electroporation. Secretion of the protein occurred at the neutral pH during induction, with optimized concentration of the inducer and presence of serine proteases inhibitor. Using Western blotting and amino acid sequencing method we found that TRAIL was secreted in two forms, as visualized by the presence of two distinct molecular size bands, both deprived of the usp45 protein, the bacterial signal peptide. By the use of MTS assay we were able to prove that hsTRAIL present in supernatant from L. lactis (hsTRAIL+) broth culture was cytotoxic to human HCT116 colon cancer cells but not to normal human fibroblasts. Flow cytometry analysis revealed TRAIL-induced apoptosis of cancer cells.

CONCLUSIONS

We designed recombinant L. lactis bacteria, which efficiently produce biologically active, anti-tumorigenic human TRAIL in vitro. Further studies in tumor-bearing NOD-SCID mice will reveal whether the TRAIL-secreting L. lactis bacteria can be used as a safe carrier of this protein, capable of inducing effective elimination of human colon cancer cells in vivo.

Highly effective renaturation of a streptokinase from Streptococcus pyogenes DT7 as inclusion bodies overexpressed in Escherichia coli

The streptokinase (SK) is emerging as an important thrombolytic therapy agent in the treatment of patients suffering from cardiovascular diseases. We reported highly effective renaturation of a SK from S. pyogeness DT7 overexpressed in E. coli, purification, and biochemical characterization. A gene coding for the SK was cloned from S. pyogeness DT7. Because accumulation of active SK is toxic to the host cells, we have expressed it in the form of inclusion bodies. The mature protein was overexpressed in E. coli BL21 DE3/pESK under the control of the strong promoter tac induced by IPTG with a level of 60% of the total cell proteins. The activity of the rSK, renatured in phosphate buffer supplemented with Triton X-100 and glycerol, was covered with up to 41 folds of its initial activity. The purified of protein was identified with MALDI-TOF mass spectrometry through four peptide fragments, which showed 100% identification to the corresponding peptides of the putative SK from GenBank. Due to overexpression and highly effective renaturation of large amounts of inclusion bodies, the recombinant E. coli BL21 DE3/pESK system could be potentially applied for large-scale production of SK used in the therapy of acute myocardial infarction.

Recombinant protein expression in Lactococcus lactis using the P170 expression system

The use of the Gram-positive bacterium Lactococcus lactis in recombinant protein production has several advantages, including the organism's long history of safe use in food production and the fact that it does not produce endotoxins. Furthermore the current non-dairy L. lactis production strains contain few proteases and can secrete stable recombinant protein to the growth medium. The P170 expression system used for recombinant protein production in L. lactis utilizes an inducible promoter, P170, which is up-regulated as lactate accumulates in the growth medium. We have optimised the components of the expression system, including improved promoter strength, signal peptides and isolation of production strains with increased productivity. Recombinant proteins are produced in a growth medium with no animal-derived components as a simple batch fermentation requiring minimal process control. The accumulation of lactate in the growth medium does, however, inhibit growth and limits the yield from batch and fed-batch processes. We therefore combined the P170 expression system with the REED™ technology, which allows control of lactate concentration by electro-dialysis during fermentation. Using this combination, production of the Staphylococcus aureus nuclease reached 2.5 g L(-1).

HtrA is essential for efficient secretion of recombinant proteins by Lactococcus lactis

HtrA is a unique protease on the extracellular surface of Lactococcus lactis. It is known to take part in the proteolysis of many secreted recombinant proteins, and the mutation of htrA can lead to the complete stabilization of recombinant proteins. In this work, we have shown that htrA mutation also leads to significant reduction of the efficiency of recombinant-protein secretion. We also show that the level of HtrA can be lowered by the suppression of the acid tolerance response (ATR) in L. lactis. Instead of using an L. lactis htrA mutant, the reduction of the HtrA level in wild-type recombinant cultures of L. lactis by ATR suppression may serve as a better strategy for the production of secreted recombinant proteins.

Functional secretion of a type 1 antifreeze protein analogue by optimization of promoter, signal peptide, prosequence, and terminator in Lactococcus lactis

Lactococcus lactis is a food-grade microorganism of major commercial importance. Antifreeze protein is a potent cryogenic protection agent for the cryopreservation of food and pharmaceutical materials. In this study, extracellular expression of a novel recombinant type I antifreeze protein analogue (rAFP) in L. lactis was optimized. An efficient SlpA promoter (P SlpA) was fused to various signal peptides (SPs) and propeptide sequences to examine the extracellular expression levels of rAFP. An efficient signal peptide, SP sacB, fused to prosequence AE, enabled higher extracellular rAFP production; use of the SlpA terminator (Ter SlpA) was a further improvement. The extracellularly expressed rAFP successfully inhibited ice recrystallization and is thus potentially applicable for cryogenic preservation.

Extracellular expression of a functional recombinant Ganoderma lucidium immunomodulatory protein by Bacillus subtilis and Lactococcus lactis

Bacillus subtilis and Lactococcus lactis are ideal hosts for the production of extracellular heterologous proteins of major commercial importance. A recombinant gene for the novel Ganoderma lucidium immunomodulatory protein LZ-8, recombinant LZ-8, was designed encoding the same amino acid sequence but using the preferred codons for both strains and was synthesized by overlapping extension PCR. Using the signal peptide (SP) from subtilisin YaB (SP(YaB)), recombinant LZ-8 was expressed extracellularly in Bacillus subtilis and Lactococcus lactis. In the absence of SP(YaB), recombinant LZ-8 was expressed extracellularly in B. subtilis, but not in L. lactis. The three expressed recombinant LZ-8s showed different capacities for modulating the production of Th1 and Th2 cytokines by peripheral blood mononuclear cells and of tumor necrosis factor alpha by a macrophage cell line.

Induction of mucosal and systemic immune responses following oral immunization of mice with Lactococcus lactis expressing human papillomavirus type 16 L1

Human papillomavirus type 16 L1 (HPV16 L1) has shown considerable promise as a parenteral vaccine for prevention of cervical cancers. Here, we report the possibility of oral vaccination for HPV16 L1 using Lactococcus lactis (L. lactis) as a live vector. L. lactis MG1363 was transformed with two types of HPV16 L1-encoding plasmids for intracellular expression or secretion. L. lactis transformed with HPV16 L1-encoding plasmids retained biochemical lactic acid production capability. The mucosal and systemic immune responses were affected by the cellular location of expressed HPV16 L1 proteins in L. lactis. Serum IgG responses were induced after oral immunizations of L. lactis secreting HPV16 L1. Vaginal IgA immune responses were observed following oral immunization with L. lactis expressing HPV16 L1 in an intracellular form, but not with L. lactis secreting HPV16 L1. Furthermore, induction of HPV16 L1-specific mucosal immune responses was affected by immunization frequency. Six immunizations over 5 weeks were required to induce vaginal immune responses. The levels of HPV16 L1-specific vaginal IgA were maintained until 12 weeks after the first vaccination. These results suggest the feasibility of L. lactis as an oral vaccine vehicle of HPV16 L1 and demonstrate the importance of cellular loci of expressed antigen for induction of vaginal and systemic immune responses.

Recombinant production of Streptococcus equisimilis streptokinase by Streptomyces lividans

Background

Streptokinase (SK) is a potent plasminogen activator with widespread clinical use as a thrombolytic agent. It is naturally secreted by several strains of beta-haemolytic streptococci. The low yields obtained in SK production, lack of developed gene transfer methodology and the pathogenesis of its natural host have been the principal reasons to search for a recombinant source for this important therapeutic protein. We report here the expression and secretion of SK by the Gram-positive bacterium Streptomyces lividans. The structural gene encoding SK was fused to the Streptomyces venezuelae CBS762.70 subtilisin inhibitor (vsi) signal sequence or to the Streptomyces lividans xylanase C (xlnC) signal sequence. The native Vsi protein is translocated via the Sec pathway while the native XlnC protein uses the twin-arginine translocation (Tat) pathway.

Results

SK yield in the spent culture medium of S. lividans was higher when the Sec-dependent signal peptide mediates the SK translocation. Using a 1.5 L fermentor, the secretory production of the Vsi-SK fusion protein reached up to 15 mg SK/l. SK was partially purified from the culture supernatant by DEAE-Sephacel chromatography. A 44-kDa degradation product co-eluted with the 47-kDa mature SK. The first amino acid residues of the S. lividans-produced SK were identical with those of the expected N-terminal sequence. The Vsi signal peptide was thus correctly cleaved off and the N-terminus of mature Vsi-SK fusion protein released by S. lividans remained intact. This result also implicates that the processing of the recombinant SK secreted by Streptomyces probably occurred at its C-terminal end, as in its native host Streptococcus equisimilis. The specific activity of the partially purified Streptomyces-derived SK was determined at 2661 IU/mg protein.

Conclusion

Heterologous expression of Streptococcus equisimilis ATCC9542 skc-2 in Streptomyces lividans was successfully achieved. SK can be translocated via both the Sec and the Tat pathway in S. lividans, but yield was about 30 times higher when the SK was fused to the Sec-dependent Vsi signal peptide compared to the fusion with the Tat-dependent signal peptide of S. lividans xylanase C. Small-scale fermentation led to a fourfold improvement of secretory SK yield in S. lividans compared to lab-scale conditions. The partially purified SK showed biological activity. Streptomyces lividans was shown to be a valuable host for the production of a world-wide important, biopharmaceutical product in a bio-active form.