Recombinant pediocin in Lactococcus lactis: increased production by propeptide fusion and improved potency by co-production with PedC

Optimized recombinant production of the bacteriocin garvicin Q by Corynebacterium glutamicum

Bacteriocins are antimicrobial peptides applied in food preservation and are interesting candidates as alternatives to conventional antibiotics or as microbiome modulators. Recently, we established Corynebacterium glutamicum as a suitable production host for various bacteriocins including garvicin Q (GarQ). Here, we establish secretion of GarQ by C. glutamicum via the Sec translocon achieving GarQ titers of about 7 mg L-1 in initial fermentations. At neutral pH, the cationic peptide is efficiently adsorbed to the negatively charged envelope of producer bacteria limiting availability of the bacteriocin in culture supernatants. A combination of CaCl2 and Tween 80 efficiently reduces GarQ adsorption to C. glutamicum. Moreover, cultivation in minimal medium supplemented with CaCl2 and Tween 80 improves GarQ production by C. glutamicum to about 15 mg L-1 but Tween 80 resulted in reduced GarQ activity at later timepoints. Using a reporter strain and proteomic analyses, we identified HtrA, a protease associated with secretion stress, as another potential factor limiting GarQ production. Transferring production to HtrA-deficient C. glutamicum K9 improves GarQ titers to close to 40 mg L-1. Applying conditions of low aeration prevented loss in activity at later timepoints and improved GarQ titers to about 100 mg L-1. This is about 50-fold higher than previously shown with a C. glutamicum strain employing the native GarQ transporter GarCD for secretion and in the range of levels observed with the native producer Lactococcus petauri B1726. Additionally, we tested several synthetic variants of GarQ and were able to show that exchange of the methionine in position 5 to a phenylalanine (GarQM5F) results in markedly increased activity against Lactococcus lactis and Listeria monocytogenes. In summary, our findings shed light on several aspects of recombinant GarQ production that may also be of relevance for production with natural producers and other bacteriocins.

Selection of lactic acid bacteria as biopreservation agents and optimization of their mode of application for the control of Listeria monocytogenes in ready-to-eat cooked meat products

In order to meet consumers´ demands for more natural foods and to find new methods to control foodborne pathogens in them, research is currently being focused on alternative preservation approaches, such as biopreservation with lactic acid bacteria (LAB). Here, a collection of lactic acid bacteria (LAB) isolates was characterized to identify potential biopreservative agents. Six isolates (one Lactococcus lactis, one Lacticaseibacillus paracasei and four Lactiplantibacillus plantarum) were selected based on their antimicrobial activity in in vitro assays. Whole genome sequencing showed that none of the six LAB isolates carried known virulence factors or acquired antimicrobial resistance genes, and that the L. lactis isolate was potentially a nisin Z producer. Growth of L. monocytogenes was successfully limited by L. lactis ULE383, L. paracasei ULE721 and L. plantarum ULE1599 throughout the shelf-life of cooked ham, meatloaf and roasted pork shoulder. These LAB isolates were also applied individually or as a cocktail at different inoculum concentrations (4, 6 and 8 log10 CFU/g) in challenge test studies involving cooked ham, showing a stronger anti-Listerial activity when a cocktail was used at 8 log10 CFU/g. Thus, a reduction of up to ~5.0 log10 CFU/g in L. monocytogenes growth potential was attained in cooked ham packaged under vacuum, modified atmosphere packaging or vacuum followed by high pressure processing (HPP). Only minor changes in color and texture were induced, although there was a significant acidification of the product when the LAB cultures were applied. Remarkably, this acidification was delayed when HPP was applied to the LAB inoculated batches. Metataxonomic analyses showed that the LAB cocktail was able to grow in the cooked ham and outcompete the indigenous microbiota, including spoilage microorganisms such as Brochothrix. Moreover, none of the batches were considered unacceptable in a sensory evaluation. Overall, this study shows the favourable antilisterial activity of the cocktail of LAB employed, with the combination of HPP and LAB achieving a complete inhibition of the pathogen with no detrimental effects in physico-chemical or sensorial evaluations, highlighting the usefulness of biopreservation approaches involving LAB for enhancing the safety of cooked meat products.

Contribution of omics to biopreservation: Toward food microbiome engineering

Biopreservation is a sustainable approach to improve food safety and maintain or extend food shelf life by using beneficial microorganisms or their metabolites. Over the past 20 years, omics techniques have revolutionised food microbiology including biopreservation. A range of methods including genomics, transcriptomics, proteomics, metabolomics and meta-omics derivatives have highlighted the potential of biopreservation to improve the microbial safety of various foods. This review shows how these approaches have contributed to the selection of biopreservation agents, to a better understanding of the mechanisms of action and of their efficiency and impact within the food ecosystem. It also presents the potential of combining omics with complementary approaches to take into account better the complexity of food microbiomes at multiple scales, from the cell to the community levels, and their spatial, physicochemical and microbiological heterogeneity. The latest advances in biopreservation through omics have emphasised the importance of considering food as a complex and dynamic microbiome that requires integrated engineering strategies to increase the rate of innovation production in order to meet the safety, environmental and economic challenges of the agri-food sector.

A novel approach of recombinant laterosporulin production using the N-SH2 domain of SHP-2

Background

The current study was aimed at evaluating the role of the N-SH2 domain of SHP-2 as a partner protein in the expression of a toxic peptide, laterosporulin (LTS). We also investigated its effects on the formation of the disulfide bond and functional folding of the peptide in vitro. The N-SH2-LTS protein was expressed as a His-tagged fusion protein, capable of undergoing enzymatic cleavage.

Results

Based on the data presented herein, the total yield of the folded fusion protein from inclusion bodies was found to be about 105 mg/l, demonstrating a high-level of heterologous expression. After enzymatic cleavage, 1.5 mg of the folded recombinant laterosporulin was obtained from each 10 mg of the fusion protein. The purity of the recombinant laterosporulin was analyzed by RP-HPLC, to yield peptides with suitable purity (85%).

Conclusions

Our findings indicated the advantages of using the N-SH2 domain of SHP-2 as a rapid and easy approach not only in producing easy target proteins but also in its function as a chaperone. N-SH2 domain of SHP-2 can influence on the purification of laterosporulin at reasonable yield and in a cost-effective fashion. The N-SH2 domain of SHP-2 as a protein chaperone may be potentially favorable to produce other proteins with disulfide bonds.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-021-00721-7.

Application of lactic acid bacteria for the biopreservation of meat products: A systematic review

The increasing concern of consumers about food quality and safety and their rejection of chemical additives has promoted the breakthrough of the biopreservation field and the development of studies on the use of beneficial bacteria and their metabolites as potential natural antimicrobials for shelf life extension and enhanced food safety. Control of foodborne pathogens in meat and meat products represents a serious challenge for the food industry which can be addressed through the intelligent use of bio-compounds or biopreservatives. This article aims to systematically review the available knowledge about biological strategies based on the use of lactic acid bacteria to control the proliferation of undesirable microorganisms in different meat products. The outcome of the literature search evidenced the potential of several strains of lactic acid bacteria and their purified or semi-purified antimicrobial metabolites as biopreservatives in meat products for achieving longer shelf life or inhibiting spoilage and pathogenic bacteria, especially when combined with other technologies to achieve a synergistic effect.

Evasin-displaying lactic acid bacteria bind different chemokines and neutralize CXCL8 production in Caco-2 cells

Chemokines are key signals in the immune system and play an important role as proinflammatory mediators in the pathology of inflammatory bowel disease and colorectal cancer, making them an important target for therapy. Recombinant lactic acid bacteria (LAB) were engineered to bind CC and CXC chemokines by displaying chemokine‐binding proteins evasin‐1, evasin‐3 and evasin‐4 on their surface. Evasin genes were cloned into lactococcal surface display vector and overexpressed in L. lactis NZ9000 and NZ9000ΔhtrA in fusion with secretion signal and surface anchor. Evasin‐displaying bacteria removed from 15% to 90% of 11 different chemokines from the solution as determined with ELISA and Luminex multiplexing assays, whereby L. lactis NZ9000ΔhtrA proved more efficient. Lactobacillus salivarius ATCC 11741 was coated with L. . lactis‐expressed evasin fusion protein, and its ability to bind chemokines was also confirmed. Evasin‐3‐displaying L. lactis removed 76.0% of IL‐1β‐induced CXCL8 from the supernatant of Caco‐2 epithelial cells. It also prevented secretion of CXCL8 from Caco‐2 cells in a time‐dependent manner when added before induction with IL‐1β. Evasin‐displaying LAB have the ability to bind multiple chemokines simultaneously and exert synergistic activity. This innovative treatment approach therefore has the potential for mucosal therapy of inflammatory bowel disease or colorectal cancer.

Draft Genome Sequence of Carnobacterium divergens V41, a Bacteriocin-Producing Strain

In this study, we present the draft genome sequence of Carnobacterium divergens V41. This strain was previously reported as producing divercin V41, a bacteriocin of interest for food biopreservation. Its genome revealed also the presence of a gene cluster putatively involved in polyketide production, which is unique in lactic acid bacteria.

Thiol-Disulfide Exchange in Gram-Positive Firmicutes

Extracytoplasmic thiol-disulfide oxidoreductases (TDORs) catalyze the oxidation, reduction, and isomerization of protein disulfide bonds. Although these processes have been characterized in Gram-negative bacteria, the majority of Gram-positive TDORs have only recently been discovered. Results from recent studies have revealed distinct trends in the types of TDOR used by different groups of Gram-positive bacteria, and in their biological functions. Actinobacteria TDORs can be essential for viability, while Firmicute TDORs influence various physiological processes, including protein stability, oxidative stress resistance, bacteriocin production, and virulence. In this review we discuss the diverse extracytoplasmic TDORs used by Gram-positive bacteria, with a focus on Gram-positive Firmicutes.

Recombinant pediocin in Lactococcus lactis: increased production by propeptide fusion and improved potency by co-production with PedC

We describe the impact of two propeptides and PedC on the production yield and the potency of recombinant pediocins produced in Lactococcus lactis. On the one hand, the sequences encoding the propeptides SD or LEISSTCDA were inserted between the sequence encoding the signal peptide of Usp45 and the structural gene of the mature pediocin PA‐1. On the other hand, the putative thiol‐disulfide oxidoreductase PedC was coexpressed with pediocin. The concentration of recombinant pediocins produced in supernatants was determined by enzyme‐linked immunosorbent assay. The potency of recombinant pediocins was investigated by measuring the minimal inhibitory concentration by agar well diffusion assay. The results show that propeptides SD or LEISSTCDA lead to an improved secretion of recombinant pediocins with apparently no effect on the antibacterial potency and that PedC increases the potency of recombinant pediocin. To our knowledge, this study reveals for the first time that pediocin tolerates fusions at the N‐terminal end. Furthermore, it reveals that only expressing the pediocin structural gene in a heterologous host is not sufficient to get an optimal potency and requires the accessory protein PedC. In addition, it can be speculated that PedC catalyses the correct formation of disulfide bonds in pediocin.