Lactococcus lactis M4, a potential host for the expression of heterologous proteins

Bioengineering of a Lactococcus lactis subsp. lactis strain enhances nisin production and bioactivity

Lactococcus lactis subsp. lactis is a food bacterium that has been utilized for decades in food fermentation and the development of high-value industrial goods. Among these, nisin, which is produced by several strains of L. lactis subsp. lactis, plays a crucial role as a food bio-preservative. The gene expression for nisin synthesis was evaluated using qPCR analysis. Additionally, a series of re-transformations of the strain introducing multiple copies of the nisA and nisRK genes related to nisin production were developed. The simultaneous expression of nisA and nisZ genes was used to potentiate the effective inhibition of foodborne pathogens. Furthermore, qPCR analysis indicated that the nisA and nisRK genes were expressed at low levels in wild-type L. lactis subsp. lactis. After several re-transformations of the strain with the nisA and nisRK genes, a high expression of these genes was obtained, contributing to improved nisin production. Also, co-expression of the nisA and nisZ genes resulted in extremely effective antibacterial action. Hence, this study would provide an approach to enhancing nisin production during industrial processes and antimicrobial activity.

Lactococcus lactis, an Attractive Cell Factory for the Expression of Functional Membrane Proteins

Membrane proteins play key roles in most crucial cellular processes, ranging from cell-to-cell communication to signaling processes. Despite recent improvements, the expression of functionally folded membrane proteins in sufficient amounts for functional and structural characterization remains a challenge. Indeed, it is still difficult to predict whether a protein can be overproduced in a functional state in some expression system(s), though studies of high-throughput screens have been published in recent years. Prokaryotic expression systems present several advantages over eukaryotic ones. Among them, Lactococcus lactis (L. lactis) has emerged in the last two decades as a good alternative expression system to E. coli. The purpose of this chapter is to describe L. lactis and its tightly inducible system, NICE, for the effective expression of membrane proteins from both prokaryotic and eukaryotic origins.

A critical review of antibiotic resistance in probiotic bacteria

Probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit upon the host. At present, probiotics are gaining popularity worldwide and are widely used in food and medicine. Consumption of probiotics is increasing with further in-depth research on the relationship between intestinal flora and host health. Most people pay more attention to the function of probiotics but ignore their potential risks, such as infection and antibiotic resistance transfer to pathogenic microbes. Physiological functions, effects and mechanisms of action of probiotics were covered in this review, as well as the antibiotic resistance phenotypes, mechanisms and genes found in probiotics. Typical cases of antibiotic resistance of probiotics were also highlighted, as well as the potential risks (including pathogenicity, infectivity and excessive immune response) and corresponding strategies (dosage, formulation, and administration route). This timely study provides an avenue for further research, development and application of probiotics.

Secretion of recombinant xylanase in Lactococcus lactis using signal peptides Usp45 and Spk1

OBJECTIVE

The effect of two signal peptides, namely Usp45 and Spk1 on the secretion of xylanase in Lactococcus lactis was analysed.

RESULTS

Xylanase was successfully expressed in Lactococcus lactis. Recombinant xylanase fused to either signal peptide Usp45 or Spk1 showed halo zone on Remazol Brilliant Blue-Xylan plates. This indicated that the xylanase was successfully secreted from the cell. The culture supernatants of strains secreting the xylanase with help of the Spk1 and Usp45 signal peptides contained 49.7 U/ml and 34.4 U/ml of xylanase activity, respectively.

CONCLUSION

Although Usp45 is the most commonly used signal peptide when secreting heterologous proteins in Lactococcus lactis, this study shows that Spk1 isolated from Pediococcus pentosaceus was superior to Usp45 in regard to xylanase protein secretion.

Oral immunization with LacVax® OmpA induces protective immune response against Shigella flexneri 2a ATCC 12022 in a murine model

Shigellosis is an acute invasive disease of the lower intestine, which afflicts millions of people worldwide with an estimated one million fatalities per annum. Despite of extensive research during the last two decades, a vaccine against multi-drug resistant Shigella is not yet available in the market. To provide a safe, effective and broad-spectrum vaccine against Shigella, we explored food grade bacteria Lactococcus lactis (L. lactis) for the delivery of conserved antigenic protein; Outer membrane protein A (OmpA) to the mucosal sites for effective elicitation of systemic and mucosal immunity. We have previously confirmed the immunogenic potential of recombinant L. lactis expressing OmpA (LacVax® OmpA) in BALB/c mice. In the present study, we have characterized the humoral and cellular immune profile of LacVax® OmpA and assessed its protective efficacy using a newly developed human like murine shigellosis model. The significant increase in OmpA specific serum IgG, fecal sIgA and a Th1 dominant immune response (indicated by high INF-γ/IL-4 ratio) in LacVax® OmpA immunized mice revealed successful activation of humoral and cellular immunity. The LacVax® OmpA immunized animals were also protected from human-like shigellosis when challenged with S. flexneri 2a ATCC 12022. The antigen specific serum IgG, fecal sIgA, INF-γ and IL-10 levels were found to be the significant correlates of protection. Collectively these results suggest that the LacVax® OmpA is a promising prophylactic candidate against shigellosis. However, the protective efficacy of LacVax® OmpA in the higher animals would further strengthen its future application in humans.

Expression of surface-bound nonstructural 1 (NS1) protein of influenza virus A H5N1 on Lactobacillus casei strain C1

The study aimed to construct a recombinant Lactobacillus casei expressing the nonstructural (NS) 1 protein of influenza A virus H5N1 on its cell wall. The NS1 gene was first amplified and fused to the pSGANC332 expression plasmid. The NS1 protein expression was carried out by Lact. casei strain C1. PCR screening and DNA sequencing confirmed the presence of recombinant pSG-NS1-ANC332 plasmid in Lact. casei. The plasmid was stably maintained (98·94 ± 1·65%) by the bacterium within the first 20 generations without selective pressure. The NS1 was expressed as a 49-kDa protein in association with the anchoring peptide. The yield was 1·325 ± 0·065 μg mg^-1 of bacterial cells. Lactobacillus casei expressing the NS1 on its cell wall was red-fluorescently stained, but the staining was not observed on Lact. casei carrying the empty pSGANC332. The results implied that Lact. casei strain C1 is a promising host for the expression of surface-bound NS1 protein using the pSGANC332 expression plasmid.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study has demonstrated, for the first time, the expression of nonstructural 1 (NS1) protein of influenza A virus H5N1 on the cell wall of Lactobacillus casei using the pSGANC332 expression plasmid. Display of NS1 protein on the bacterial cell wall was evident under an immunofluorescence microscopic observation. Lactobacillus casei carrying the NS1 protein could be developed into a universal oral influenza vaccine since the NS1 is highly conserved among influenza viruses.

Bacteriocin-Producing Lactic Acid Bacteria Isolated from Mangrove Forests in Southern Thailand as Potential Bio-Control Agents: Purification and Characterization of Bacteriocin Produced by Lactococcus lactis subsp. lactis KT2W2L

The aim of this work was to purify and characterize the bacteriocin produced by Lactococcus lactis subsp. lactis KT2W2L previously isolated from mangrove forests in southern Thailand, in order to evaluate its potential as new food protective agent. The active peptide from the cell-free supernatant of this strain was purified in 4 steps: (1) precipitation with 70 % saturated ammonium sulfate, (2) elution on a reversed-phase cartridge using different concentrations of acetonitrile, (3) cation-exchange chromatography and (4) final purification by reversed-phase HPLC on a C8 column. The molecular mass of 3,329.5254 Da of the purified bacteriocin, determined by mass spectrometry, is nearly identical to that of peptide nisin Z. The activity of the purified bacteriocin was unaffected by pH (2.0-10.0), thermostable but was sensitive to proteolytic enzymes. The bacteriocin activity was stable after 8 weeks of storage at -20 °C and 7 weeks of storage at 4 °C, but decreased after 3 weeks of storage at 37 °C. It was stable when incubated for 1 month at 4 °C in 0-30 % NaCl. Inhibitory spectrum of this bacteriocin showed a wide range of activity against similar bacterial strains, food-spoilage and food-borne pathogens. L. lactis subsp. lactis KT2W2L was sensitive to kanamycin, penicillin and tetracycline but resistant to ampicillin, gentamicin and vancomycin. The fragment obtained after amplification of genomic DNA from L. lactis subsp. lactis KT2W2L, with specific primers for bacteriocin genes, presented 99 % homology to the nisin Z gene. PCR amplification demonstrated that L. lactis subsp. lactis KT2W2L does not harbor virulence genes cylA, cylB, efaAfs and esp. The bacteriocin and its producing strain may find application as bio-preservatives for reduction in food-spoilage and food-borne pathogens in food products.

Inhibition of pathogenic and spoilage bacteria by a novel biofilm-forming Lactobacillus isolate: a potential host for the expression of heterologous proteins

BACKGROUND

Bacterial biofilms are a preferred mode of growth for many types of microorganisms in their natural environments. The ability of pathogens to integrate within a biofilm is pivotal to their survival. The possibility of biofilm formation in Lactobacillus communities is also important in various industrial and medical settings. Lactobacilli can eliminate the colonization of different pathogenic microorganisms. Alternatively, new opportunities are now arising with the rapidly expanding potential of lactic acid bacteria biofilms as bio-control agents against food-borne pathogens.

RESULTS

A new isolate Lactobacillus plantarum PA21 could form a strong biofilm in pure culture and in combination with several pathogenic and food-spoilage bacteria such as Salmonella enterica, Bacillus cereus, Pseudomonas fluorescens, and Aeromonas hydrophila. Exposure to Lb. plantarum PA21 significantly reduced the number of P. fluorescens, A. hydrophila and B. cereus cells in the biofilm over 2-, 4- and 6-day time periods. However, despite the reduction in S. enterica cells, this pathogen showed greater resistance in the presence of PA21 developed biofilm, either in the planktonic or biofilm phase. Lb. plantarum PA21 was also found to be able to constitutively express GFP when transformed with the expression vector pMG36e which harbors the gfp gene as a reporter demonstrating that the newly isolated strain can be used as host for genetic engineering.

CONCLUSION

In this study, we evaluate the ability of a new Lactobacillus isolate to form strong biofilm, which would provide the inhibitory effect against several spoilage and pathogenic bacteria. This new isolate has the potential to serve as a safe and effective cell factory for recombinant proteins.

Expanding the recombinant protein quality in Lactococcus lactis

Background

Escherichia coli has been a main host for the production of recombinant proteins of biomedical interest, but conformational stress responses impose severe bottlenecks that impair the production of soluble, proteolytically stable versions of many protein species. In this context, emerging Generally Recognized As Safe (GRAS) bacterial hosts provide alternatives as cell factories for recombinant protein production, in which limitations associated to the use of Gram-negative microorganisms might result minimized. Among them, Lactic Acid Bacteria and specially Lactococcus lactis are Gram-positive GRAS organisms in which recombinant protein solubility is generically higher and downstream facilitated, when compared to E. coli. However, deep analyses of recombinant protein quality in this system are still required to completely evaluate its performance and potential for improvement.

Results

We have explored here the conformational quality (through specific fluorescence emission) and solubility of an aggregation-prone GFP variant (VP1GFP) produced in L. lactis. In this context, our results show that parameters such as production time, culture conditions and growth temperature have a dramatic impact not only on protein yield, but also on protein solubility and conformational quality, that are particularly favored under fermentative metabolism.

Conclusions

Metabolic regime and cultivation temperature greatly influence solubility and conformational quality of an aggregation-prone protein in L. lactis. Specifically, the present study proves that anaerobic growth is the optimal condition for recombinant protein production purposes. Besides, growth temperature plays an important role regulating both protein solubility and conformational quality. Additionally, our results also prove the great versatility for the manipulation of this bacterial system regarding the improvement of functionality, yield and quality of recombinant proteins in this species. These findings not only confirm L. lactis as an excellent producer of recombinant proteins but also reveal room for significant improvement by the exploitation of external protein quality modulators.

Growth phase-dependent proteomes of the Malaysian isolated Lactococcus lactis dairy strain M4 using label-free qualitative shotgun proteomics analysis

Lactococcus lactis is the most studied mesophilic fermentative lactic acid bacterium. It is used extensively in the food industry and plays a pivotal role as a cell factory and also as vaccine delivery platforms. The proteome of the Malaysian isolated L. lactis M4 dairy strain, obtained from the milk of locally bred cows, was studied to elucidate the physiological changes occurring between the growth phases of this bacterium. In this study, ultraperformance liquid chromatography nanoflow electrospray ionization tandem mass spectrometry (UPLC- nano-ESI-MS^E) approach was used for qualitative proteomic analysis. A total of 100 and 121 proteins were identified from the midexponential and early stationary growth phases, respectively, of the L. lactis strain M4. During the exponential phase, the most important reaction was the generation of sufficient energy, whereas, in the early stationary phase, the metabolic energy pathways decreased and the biosynthesis of proteins became more important. Thus, the metabolism of the cells shifted from energy production in the exponential phase to the synthesis of macromolecules in the stationary phase. The resultant proteomes are essential in providing an improved view of the cellular machinery of L. lactis during the transition of growth phases and hence provide insight into various biotechnological applications.

Construction of a novel inducible expression vector for Lactococcus lactis M4 and Lactobacillus plantarum Pa21

A vector that drives the expression of the reporter gusA gene in both Lactobacillus plantarum and Lactococcus lactis was constructed in this study. This vector contained a newly characterized heat shock promoter (Phsp), amplified from an Enterococcus faecium plasmid, pAR6. Functionality and characterization of this promoter was initially performed by cloning Phsp into pNZ8008, a commercial lactococcal plasmid used for screening of putative promoters which utilizes gusA as a reporter. It was observed that Phsp was induced under heat, salinity and alkaline stresses or a combination of all three stresses. The newly characterized Phsp promoter was then used to construct a novel Lactobacillus vector, pAR1801 and its ability to express the gusA under stress-induced conditions was reproducible in both Lb. plantarum Pa21 and L. lactis M4 hosts.

IRES-incorporated lactococcal bicistronic vector for target gene expression in a eukaryotic system

Plasmid DNAs isolated from lactic acid bacteria (LAB) such as Lactococcus lactis (L. lactis) has been gaining more interests for its positive prospects in genetic engineering-related applications. In this study, the lactococcal plasmid, pNZ8048 was modified so as to be able to express multiple genes in the eukaryotic system. Therefore, a cassette containing an internal ribosome entry site (IRES) was cloned between VP2 gene of a very virulent infectious bursal disease (vvIBDV) UPM 04190 of Malaysian local isolates and the reporter gene, green fluorescent protein (GFP) into pNZ:CA, a newly constructed derivative of pNZ8048 harboring the cytomegalovirus promoter (Pcmv) and polyadenylation signal. The new bicistronic vector, denoted as pNZ:vig was subjected to in vitro transcription/translation system followed by SDS-PAGE and Western blot analysis to rapidly verify its functionality. Immunoblotting profiles showed the presence of 49 and 29kDa bands that corresponds to the sizes of the VP2 and GFP proteins respectively. This preliminary result shows that the newly constructed lactococcal bicistronic vector can co-express multiple genes in a eukaryotic system via the IRES element thus suggesting its feasibility to be used for transfection of in vitro cell cultures and vaccine delivery.

Intracellular production of IFN-alpha 2b in Lactococcus lactis

Human interferon alpha (IFN-α) was expressed in two strains of Lactococcus lactis by aid of two promoters (P32 and Pnis) giving rise to two recombinant strains: MG:IFN and NZ:IFN, respectively. The expression of IFN was confirmed by ELISA and western blotting. Highest production was achieved using glucose for growth of both recombinant strains with nisin, used for induction of the recombinant strain with Pnis promoter, at 30 ng/ml. The optimum time for MG:IFN was 9 h and for NZ:IFN was 4.5 h. The highest productions by MG:IFN and NZ:IFN were 1.9 and 2.4 μg IFN/l, respectively. Both of the expressed IFNs showed bioactivities of 1.9 × 10(6) IU/mg that were acceptable for further clinical studies.

How to achieve high-level expression of microbial enzymes: strategies and perspectives

Microbial enzymes have been used in a large number of fields, such as chemical, agricultural and biopharmaceutical industries. The enzyme production rate and yield are the main factors to consider when choosing the appropriate expression system for the production of recombinant proteins. Recombinant enzymes have been expressed in bacteria (e.g., Escherichia coli, Bacillus and lactic acid bacteria), filamentous fungi (e.g., Aspergillus) and yeasts (e.g., Pichia pastoris). The favorable and very advantageous characteristics of these species have resulted in an increasing number of biotechnological applications. Bacterial hosts (e.g., E. coli) can be used to quickly and easily overexpress recombinant enzymes; however, bacterial systems cannot express very large proteins and proteins that require post-translational modifications. The main bacterial expression hosts, with the exception of lactic acid bacteria and filamentous fungi, can produce several toxins which are not compatible with the expression of recombinant enzymes in food and drugs. However, due to the multiplicity of the physiological impacts arising from high-level expression of genes encoding the enzymes and expression hosts, the goal of overproduction can hardly be achieved, and therefore, the yield of recombinant enzymes is limited. In this review, the recent strategies used for the high-level expression of microbial enzymes in the hosts mentioned above are summarized and the prospects are also discussed. We hope this review will contribute to the development of the enzyme-related research field.

Unconventional microbial systems for the cost-efficient production of high-quality protein therapeutics

Both conventional and innovative biomedical approaches require cost-effective protein drugs with high therapeutic potency, improved bioavailability, biocompatibility, stability and pharmacokinetics. The growing longevity of the human population, the increasing incidence and prevalence of age-related diseases and the better comprehension of genetic-linked disorders prompt to develop natural and engineered drugs addressed to fulfill emerging therapeutic demands. Conventional microbial systems have been for long time exploited to produce biotherapeutics, competing with animal cells due to easier operation and lower process costs. However, both biological platforms exhibit important drawbacks (mainly associated to intracellular retention of the product, lack of post-translational modifications and conformational stresses), that cannot be overcome through further strain optimization merely due to physiological constraints. The metabolic diversity among microorganisms offers a spectrum of unconventional hosts, that, being able to bypass some of these weaknesses, are under progressive incorporation into production pipelines. In this review we describe the main biological traits and potentials of emerging bacterial, yeast, fungal and microalgae systems, by comparing selected leading species with well established conventional organisms with a long run in protein drug production.