A food-grade expression/secretion vector for Lactococcus lactis that uses an alpha-galactosidase gene as a selection marker

Sugar Utilization-Associated Food-Grade Selection Markers in Lactic Acid Bacteria and Yeast

This comprehensive review explores the development of food-grade selection markers in lactic acid bacteria and yeast; some of their strains are precisely defined as safe microorganisms and are crucial in the food industry. Lactic acid bacteria, known for their ability to ferment carbohydrates into lactic acid, provide essential nutrients and contribute to immune responses. With its strong fermentation capabilities and rich nutritional profile, yeast finds use in various food products. Genetic engineering in these microorganisms has grown rapidly, enabling the expression of enzymes and secondary products for food production. However, the focus is on ensuring safety, necessitating food-grade selection markers. Traditional antibiotic and heavy metal resistance selection markers pose environmental and health risks, prompting the search for safer alternatives. Complementary selection markers, such as sugar utilization markers, offer a promising solution. These markers use carbohydrates as carbon sources for growth and are associated with the natural metabolism of lactic acid bacteria and yeast. This review discusses the use of specific sugars, such as lactose, melibiose, sucrose, D-xylose, glucosamine, and N-acetylglucosamine, as selection markers, highlighting their advantages and limitations. In summary, this review underscores the importance of food-grade selection markers in genetic engineering and offers insights into their applications, benefits, and challenges, providing valuable information for researchers in the field of food microbiology and biotechnology.

Safety Aspects of Genetically Modified Lactic Acid Bacteria

Lactic acid bacteria (LAB) have a long history of use in the food industry. Some species are part of the normal human microbiota and have beneficial properties for human health. Their long-standing use and considerable biotechnological potential have led to the development of various systems for their engineering. Together with novel approaches such as CRISPR-Cas, the established systems for engineering now allow significant improvements to LAB strains. Nevertheless, genetically modified LAB (GM-LAB) still encounter disapproval and are under extensive regulatory requirements. This review presents data on the prospects for LAB to obtain 'generally recognized as safe' (GRAS) status. Genetic modification of LAB is discussed, together with problems that can arise from their engineering, including their dissemination into the environment and the spread of antibiotic resistance markers. Possible solutions that would allow the use of GM-LAB are described, such as biocontainment, alternative selection markers, and use of homologous DNA. The use of GM-LAB as cell factories in closed systems that prevent their environmental release is the least problematic aspect, and this is also discussed.

Heterologous expression of azurin from Pseudomonas aeruginosa in food-grade Lactococcus lactis

In this study, azurin, a bacteriocin with anticancer property, was produced by food-grade Lactococcus lactis using the Nisin Controlled Gene Expression (NICE) System. In addition, the antibacterial and cytotoxic properties of recombinant azurin in the culture supernatant were also investigated. Azurin gene from Pseudomonas aeruginosa was cloned into the pNZ8149 vector and the resulting recombinant DNA was transformed into food grade L. lactis NZ3900. The expression of azurin protein was induced by the optimum concentration of nisin for 3 h. Inhibition zones for Escherichia coli and Bacillus cereus were observed at 5.0 and 10 mg/mL concentrations of lyophilized supernatants containing azurin, but no inhibition zone at azurin-free lyophilized supernatants. When HUVEC, HT29, HCT116, and MCF7 cell lines were treated with lyophilized culture supernatants with azurin or without azurin, cell viability decreased with increasing concentrations of the supernatant. Furthermore, the supernatants containing azurin showed more anti-proliferative effect than the azurin-free supernatants. This work provides a practicable method to produce recombinant azurin in the food grade L. lactis strain. As a result, the recombinant L. lactis strain, producing azurin, can be used in the investigation of food biopreservatives and in the development of a therapeutic probiotic.

Lactococcus lactis-based vaccines from laboratory bench to human use: an overview

Developing effective vaccines is an important weapon in the battle against potential pathogens and their evolving antibiotic resistance trends. Several vaccine delivery vectors have been investigated among which the generally regarded as safe (GRAS) Lactococcus lactis has a distinguished position. In this review, different factors affecting the efficacy of L. lactis-based vaccines are discussed. In addition, the issues of biological containment and pharmaceutical quality assurance of L. lactis vaccines are highlighted. These issues are critical for the success of medical translation of L. lactis-based vaccines from research laboratories to clinical use by ensuring consistent manufacturing of safe and efficacious vaccines.

A food-grade industrial arming yeast expressing beta-1,3-1,4-glucanase with enhanced thermal stability

The aim of this work was to construct a novel food-grade industrial arming yeast displaying beta-1,3-1,4-glucanase and to evaluate the thermal stability of the glucanase for practical application. For this purpose, a bi-directional vector containing galactokinase (GAL1) and phosphoglycerate kinase 1 (PGK1) promoters in different orientations was constructed. The beta-1,3-1,4-glucanase gene from Bacillus subtilis was fused to alpha-agglutinin and expressed under the control of the GAL1 promoter. alpha-galactosidase induced by the constitutive PGK1 promoter was used as a food-grade selection marker. The feasibility of the alpha-galactosidase marker was confirmed by the growth of transformants harboring the constructed vector on a medium containing melibiose as a sole carbon source, and by the clear halo around the transformants in Congo-red plates owing to the expression of beta-1,3-1,4-glucanase. The analysis of beta-1,3-1,4-glucanase activity in cell pellets and in the supernatant of the recombinant yeast strain revealed that beta-1,3-1,4-glucanase was successfully displayed on the cell surface of the yeast. The displayed beta-1,3-1,4-glucanase activity in the recombinant yeast cells increased immediately after the addition of galactose and reached 45.1 U/ml after 32-h induction. The thermal stability of beta-1,3-1,4-glucanase displayed in the recombinant yeast cells was enhanced compared with the free enzyme. These results suggest that the constructed food-grade yeast has the potential to improve the brewing properties of beer.

Cloning and functional expression of an alpha-galactosidase from Yersinia pestis biovar Microtus str. 91001

A gene encoding a glycoside hydrolase (GH) family 36 alpha-galactosidase was cloned from Yersinia pestis biovar Microtus str. 91001 and expressed in Escherichia coli. The purified recombinant alpha-galactosidase (Aga-Y) was optimally active at 37 degrees C and pH 6.8. The features of temperature profile, thermoliability, kinetics, and amino acid composition indicated that Aga-Y had properties of a cold-adapted enzyme.

High-throughput identification and validation of in situ-expressed genes of Lactococcus lactis

Understanding the functional response of bacteria to their natural environment is one of the current challenges in microbiology. Over the past decades several techniques have been developed to study gene expression in complex natural habitats. Most of these methods, however, are laborious, and validation of results under in situ conditions is cumbersome. Here we report the improvement of the recombinase-based in vivo expression technology (R-IVET) by the implementation of two additional reporter genes. The first one is an alpha-galactosidase gene (melA), which facilitates the rapid identification of in vivo-induced genes. Second, the bacterial luciferase genes (luxAB) are transcriptionally coupled to the resolvase gene, which allows rapid validation and characterization of in vivo-induced genes. The system is implemented and validated in the industrially important lactic acid bacterium Lactococcus lactis. We demonstrate the applicability of the advanced R-IVET system by the identification and validation of lactococcal promoter elements that are induced in minimal medium compared to the commonly used rich laboratory medium M17. R-IVET screening led to the identification of 19 promoters that predominantly control expression of genes involved in amino acid and nucleotide metabolism and in transport functions. Furthermore, the luciferase allows high-resolution transcription analysis and enabled the identification of complex medium constituents and specific molecules involved in promoter control. Rapid target validation exemplifies the high-throughput potential of the extended R-IVET system. The system can be applied to other bacterial species, provided that the reporter genes used are functional in the organism of interest.

Protective effects of a heme oxygenase-1-secreting Lactococcus lactis on mucosal injury induced by hemorrhagic shock in rats

AIM

To investigate the protective effects of a heme oxygenase-1 (HO-1)-secreting Lactococcus lactis (LL-HO-1) on mucosal injury induced by hemorrhagic shock in rats.

METHODS

The ability of recombinant LL-HO-1 to secrete biological active HO-1 in the rat intestine was determined in situ after 3 d of daily intragastric administration. The therapeutic potential of LL-HO-1 strain was then evaluated on mucosal injury induced by hemorrhagic shock in rats. After successful resuscitation, mean arterial blood pressure was recorded at 5, 10, 20, and 30 min. One hour after resuscitation, the ileum was harvested for evaluation of mucosal injury by blinded microscopic inflammatory score (Chiu's grade 0-5), myeloperoxidase activity, bacterial translocation, and by the secretion of pro- and anti-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-10, respectively).

RESULTS

Intragastric administration of HO-1-secreting L. lactis strain led to bioactive delivery of HO-1 at intestinal mucosa and significantly enhanced mean arterial blood pressure and interleukin-10 levels. Moreover, intragastric administration of LL-HO-1 significantly decreased Chiu's score, myeloperoxidase activity, bacterial translocation, and tumor necrosis factor-alpha levels when compared with rats treated with the wild-type strain. The protective effect of recombinant LL-HO-1 could be abolished by co-administration of a HO-1 inhibitor, the zinc protoporphyrin-IX.

CONCLUSION

These results suggest that intragastric administration with HO-1-secreting L. lactis reduces mucosal injury induced by hemorrhagic shock.

Intragastric administration with recombinant Lactococcus lactis producing heme oxygenase-1 prevents lipopolysaccharide-induced endotoxemia in rats

Gut injury is a pivotal initiating event in the dysfunctional inflammatory response that causes postinjury multiple organ failure. Heme oxygenase-1 (HO-1) is an important enzyme that provides cellular protection against oxidative stress in different in vitro and in vivo systems. In this study, we evaluated the protective effects of intragastrically administered live Lactococcus lactis secreting bioactive HO-1 to treat intestinal mucosal injury induced by lipopolysaccharide in rats. Intragastric administration with this recombinant L. lactis strain led to active delivery of HO-1 at the mucosa and significantly decreased morbidity and mortality of lipopolysaccharide -induced endotoxemia as confirmed by blinded macroscopic and microscopic inflammatory scores (Chiu's grade), myeloperoxidase activity, mortality, and tumor necrosis factor-alpha and IL-10 cytokine stimulation. This protective effect could be abolished by an HO-1 inhibitor, the zinc protoporphyrin-IX. Our results suggest that a food-grade bacterium genetically modified to deliver bioactive HO-1 in situ exerts a protective effect against intestinal mucosal injury in rats with endotoxemia via modulation of the immune system. This novel approach may be beneficial for the maintenance of the intestinal barrier and anti-inflammatory response of the lower intestine.

Heterologous protein secretion by Lactobacillus plantarum using homologous signal peptides

AIMS

To test seven selected putative signal peptides from Lactobacillus plantarum WCFS1 in terms of their ability to drive secretion of two model proteins in Lact. plantarum, and to compare the functionality of these signal peptides with that of well-known heterologous signal peptides (Usp45, M6).

METHODS AND RESULTS

Signal peptide functionality was assessed using a series of modular derivatives of the pSIP vectors for peptide pheromone-controlled high-level gene expression in lactobacilli. Several of the constructs with homologous signal peptides yielded similar or higher reporter protein activities than constructs with heterologous signal peptides. Two of the homologous signal peptides (Lp_0373 and Lp_0600) appeared as especially promising candidates for directing secretion, as they were among the best performing with both reporter proteins.

CONCLUSIONS

We have identified homologous signal peptides for high-level secretion of heterologous proteins in Lact. plantarum. With the model proteins, some of these performed better than commonly used heterologous signal peptides.

SIGNIFICANCE AND IMPACT OF THE STUDY

The homologous signal peptides tested out, in this study, could be useful in food-grade systems for secretion of interesting proteins in Lact. plantarum. The constructed modular secretion vectors are easily accessible for rapid signal peptide screening.

Construction of a new food-grade expression system for Bacillus subtilis based on theta replication plasmids and auxotrophic complementation

A new food-grade expression system was constructed for Bacillus subtilis based on replicative food-grade expression plasmids and auxotrophic complementation. The food-grade B. subtilis host FG01 was created by knockout of the dal locus from the chromosome of B. subtilis 168. Two food-grade expression plasmids pXFGT03 and pXFGT05 were constructed by combining a novel theta-type Bacillus replicon with the B. subtilis endogenous gene dal and P43 promoter; while pXFGT05 was derived from pXFGT03 by deletion of two open reading frames (ORFs) from the original replicon. Upon transformation of FG01 with pXFGT03 or pXFGT05, the host phenotype was complemented on Luria-Bertani agar plates by the plasmid-coded dal gene, which served as a food-grade selection marker for recombinants. Results showed that deletion of the two ORFs had no impact on plasmid replication. A reporter gene bgaB was cloned into pXFGT03 and pXFGT05, respectively, under control of the P43 promoter, and it was successfully expressed in this food-grade expression system. Segregational stabilities of two recombinant plasmids were investigated, and they were fully stable.