Cloning, production, and functional expression of the bacteriocin sakacin A (SakA) and two SakA-derived chimeras in lactic acid bacteria (LAB) and the yeasts Pichia pastoris and Kluyveromyces lactis

Mining, heterologous expression, purification, antibactericidal mechanism, and application of bacteriocins: A review

Bacteriocins are generally considered as low-molecular-weight ribosomal peptides or proteins synthesized by G⁺ and G^- bacteria that inhibit or kill other related or unrelated microorganisms. However, low yield is an important factor restricting the application of bacteriocins. This paper reviews mining methods, heterologous expression in different systems, the purification technologies applied to bacteriocins, and identification methods, as well as the antibacterial mechanism and applications in three different food systems. Bioinformatics improves the efficiency of bacteriocins mining. Bacteriocins can be heterologously expressed in different expression systems (e.g., Escherichia coli, Lactobacillus, and yeast). Ammonium sulfate precipitation, dialysis membrane, pH-mediated cell adsorption/desorption, solvent extraction, macroporous resin column, and chromatography are always used as purification methods for bacteriocins. The bacteriocins are identified through electrophoresis and mass spectrum. Cell envelope (e.g., cell permeabilization and pore formation) and inhibition of gene expression are common antibacterial mechanisms of bacteriocins. Bacteriocins can be added to protect meat products (e.g., beef and sausages), dairy products (e.g., cheese, milk, and yogurt), and vegetables and fruits (e.g., salad, apple juice, and soybean sprouts). The future research directions are also prospected.

Improving the Yield of Xenocoumacin 1 Enabled by In Situ Product Removal

Xenocoumacin 1 (Xcn1), a major antimicrobial compound produced by Xenorhabdus nematophila CB6, has great potential to be developed into a novel biofungicide. However, its low yield in the producing cells has limited its possible commercial applications. In this study, we explored the effect of in situ product removal (ISPR), a well-established recovery technique, with the use of macroporous resin X-5 on the production of Xcn1 in a fermentation setting. Relative to the routine fermentation process, the yield of Xcn1 was improved from 42.5 to 73.8 μg/mL (1.7-fold) and 12.9 to 60.3 μg/mL (4.7-fold) in three and ten days, respectively. By agar diffusion plate and growth inhibition assays, the antibiotic activity against Bacillus subtilis and Alternaria solani was also found to be improved. Further study revealed that protection of Xcn1 against degradation and decrease in cell self-toxicity as well as upregulation of biosynthesis-related genes of Xcn1 at the transcription level contributed to yield improvement of Xcn1. In addition, resin X-5 significantly altered the metabolite profile of X. nematophila CB6, which could promote the discovery of new antibiotics.

Expression and Purification of Hybrid LL-37Tα1 Peptide in Pichia pastoris and Evaluation of Its Immunomodulatory and Anti-inflammatory Activities by LPS Neutralization

This study pertains to the new approach for the development of hybrid peptide LL-37Tα1 and its biomedical applications. A linear cationic hybrid peptide, LL-37Tα1 was derived from two parental peptides (LL-37 and Tα1) recognized as potent anti-endotoxin without any hemolytic or cytotoxic activity. We successfully cloned the gene of hybrid peptide LL-37Tα1 in PpICZαA vector and expressed in the Pichia pastoris. The recombinant peptide was purified by Ni-affinity column and reverse-phase high performance liquid chromatography (RP-HPLC) with an estimated molecular mass of 3.9 kDa as determined by SDS-PAGE and mass spectrometry. We analyzed the LPS neutralization by limulus amebocyte lysate (LAL) activity and the results indicate that the hybrid peptide LL-37Tα1 directly binds endotoxin and significantly (p < 0.05) neutralizes the effect of LPS in a dose-dependent manner. Lactate dehydrogenase (LDH) assay revealed that LL-37Tα1 successfully reduces the LPS-induced cytotoxicity in mouse RAW264.7 macrophages. Moreover, it significantly (p < 0.05) decreased the levels of nitric oxide, proinflammatory cytokines including TNF-α, IL-6, IL-1β, and diminished the number of apoptotic cells in LPS-stimulated mouse RAW264.7 macrophages. Our results suggest that the P. pastoris expression system is cost-effective for commercial production of the immunomodulatory and anti-inflammatory hybrid peptide (IAHP) LL-37Tα1 and the peptide may serve as effective anti-endotoxin/anti-inflammatory agent with minimal cytotoxicity.

Design, expression, and characterization of the hybrid antimicrobial peptide T-catesbeianin-1 based on FyuA

The overuse of antibiotics has resulted in the emergence of antibiotic-resistant bacteria, which presents an urgent need for new antimicrobial agents. At present, antimicrobial peptides have attracted a great deal of attention from researchers. However, antimicrobial peptides often affect a broad range of microorganisms, including the normal flora in a host organism. In the present study, we designed a novel hybrid antimicrobial peptide, expressed the hybrid peptide, and studied its specific target. The hybrid peptide, named T-catesbeianin-1, which includes the FyuA-binding domain of pesticin and the peptide catesbeianin-1, was designed and expressed in Pichia pastoris X-33. Then, we determined the antimicrobial activity, cytotoxicity, and specific target of the peptide. T-catesbeianin-1 has strong antimicrobial activity and binds to FyuA to inhibit or kill Escherichia coli present in clinical specimens and mixed-species culture. In summary, these findings suggested that T-catesbeianin-1 might be promising and specific antibiotic agent for therapeutic application against fyuA⁺ E. coli.

Isolation of thermotolerant yeast Pichia kudriavzevii from nuruk

Thermotolerant yeast strains were isolated from nuruk, a traditional Korean fermentation starter in which variety of microorganisms are present. Among the isolates, the MBY1358 identified as yeast Pichia kudriavzevii showed significantly higher growth rate (0.59 ± 0.00 1/h) at 44 °C than other strains. Maximum ethanol concentration of 8.35 ± 0.03 g/L was obtained from 20 g/L glucose with yield of 0.44 ± 0.01 g/g at 44 °C, which is 1.14 times ethanol production of the control strain of P. kudriavzevii. The MBY1358, which was significantly more thermotolerant than the control strain and fermented 200 g/L glucose to 107.33 ± 5.03 g/L ethanol at 44 °C, was deposited to Korean Collection for Type Cultures (KCTC) under the accession number 27654.

Controlled functional expression of the bacteriocins pediocin PA-1 and bactofencin A in Escherichia coli

The bacteriocins bactofencin A (class IId) and pediocin PA-1 (class IIa) are encoded by operons with a similarly clustered gene organization including a structural peptide, an immunity protein, an ABC transporter and accessory bacteriocin transporter protein. Cloning of these operons in E. coli Tuner^TM (DE3) on a pETcoco-2 derived vector resulted in successful secretion of both bacteriocins. A corresponding approach, involving the construction of vectors containing different combinations of these genes, revealed that the structural and the transporter genes alone are sufficient to permit heterologous production and secretion in this host. Even though the accessory protein, usually associated with optimal disulfide bond formation, was not required for bacteriocin synthesis, its presence did result in greater pediocin PA-1 production. The simplicity of the system and the fact that the associated bacteriocins could be recovered from the extracellular medium provides an opportunity to facilitate protein engineering and the overproduction of biologically-active bacteriocins at industrial scale. Additionally, this system could enable the characterization of new bacteriocin operons where genetic tools are not available for the native producers.

Solution Structure of Enterocin HF, an Antilisterial Bacteriocin Produced by Enterococcus faecium M3K31

The solution structure of enterocin HF (EntHF), a class IIa bacteriocin of 43 amino acids produced by Enterococcus faecium M3K31, was evaluated by CD and NMR spectroscopy. Purified EntHF was unstructured in water, but CD analysis supports that EntHF adopts an α-helical conformation when exposed to increasing concentrations of trifluoroethanol. Furthermore, NMR spectroscopy indicates that this bacteriocin adopts an antiparallel β-sheet structure in the N-terminal region (residues 1-17), followed by a well-defined central α-helix (residues 19-30) and a more disordered C-terminal end (residues 31-43). EntHF could be structurally organized into three flexible regions that might act in a coordinated manner. This is in agreement with the absence of long-range nuclear Overhauser effect signals between the β-sheet domain and the C-terminal end of the bacteriocin. The 3D structure recorded for EntHF fits emerging facts regarding target recognition and mode of action of class IIa bacteriocins.

Cloning strategies for heterologous expression of the bacteriocin enterocin A by Lactobacillus sakei Lb790, Lb. plantarum NC8 and Lb. casei CECT475

Background

Bacteriocins produced by lactic acid bacteria (LAB) attract considerable interest as natural and nontoxic food preservatives and as therapeutics whereas the bacteriocin-producing LAB are considered potential probiotics for food, human and veterinary applications, and in the animal production field. Within LAB the lactobacilli are increasingly used as starter cultures for food preservation and as probiotics. The lactobacilli are also natural inhabitants of the gastrointestinal (GI) tract and attractive vectors for delivery of therapeutic peptides and proteins, and for production of bioactive peptides. Research efforts for production of bacteriocins in heterologous hosts should be performed if the use of bacteriocins and the LAB bacteriocin-producers is ever to meet the high expectations deposited in these antimicrobial peptides. The recombinant production and functional expression of bacteriocins by lactobacilli would have an additive effect on their probiotic functionality.

Results

The heterologous production of the bacteriocin enterocin A (EntA) was evaluated in different Lactobacillus spp. after fusion of the versatile Sec-dependent signal peptide (SP_usp45) to mature EntA plus the EntA immunity gene (entA + entiA) (fragment UAI), and their cloning into plasmid vectors that permitted their inducible (pSIP409 and pSIP411) or constitutive (pMG36c) production. The amount, antimicrobial activity (AA) and specific antimicrobial activity (SAA) of the EntA produced by Lactobacillus sakei Lb790, Lb. plantarum NC8 and Lb. casei CECT475 transformed with the recombinant plasmids pSIP409UAI, pSIP411UAI and pMGUAI varied depending of the expression vector and the host strain. The Lb. casei CECT475 recombinant strains produced the largest amounts of EntA, with the highest AA and SAA. Supernatants from Lb. casei CECT (pSIP411UAI) showed a 4.9-fold higher production of EntA with a 22.8-fold higher AA and 4.7-fold higher SAA than those from Enterococcus faecium T136, the natural producer of EntA. Moreover, supernatants from Lb. casei CECT475 (pSIP411UAI) showed a 15.7- to 59.2-fold higher AA against Listeria spp. than those from E. faecium T136.

Conclusion

Lb. casei CECT457 (pSIP411UAI) may be considered a promising recombinant host and cell factory for the production and functional expression of the antilisterial bacteriocin EntA.

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.

Genetic characterization and expression of leucocin B, a class IId bacteriocin from Leuconostoc carnosum 4010

Leuconostoc carnosum 4010 is an antimicrobial strain used as a protective culture in vacuum-packed meats. In this study, we showed that, in addition to antilisterial class IIa bacteriocins leucocin A and C, the strain also produces class IId bacteriocin leucocin B, the antimicrobial activity of which is limited to the genera Leuconostoc and Weissella. Two novel genes, lebBI encoding the leucocin B precursor with a double-glycine-type leader and putative immunity protein LebI, were identified on L. carnosum 4010 plasmid pLC4010-1. LebI contains three transmembrane spans and shares 55% identity with the mesentericin B105 immunity protein. Genes lebBI were shown to be transcribed in 4010 by RT-PCR analysis. The secretion of leucocin B in L. carnosum 4010 was shown by spot-on-lawn and SDS-gel overlay methods with a Leuconostoc strain sensitive to leucocin B but resistant to leucocins A and C. In addition, leucocins A and B from L. carnosum 4010 were cloned as SSusp45 fusions in heterologous host Lactococcus lactis and the secretion of active bacteriocins was detected on indicator plates.

High-throughput screening assays for antibacterial and antifungal activities of Lactobacillus species

We describe high-throughput screening techniques to rapidly detect either antimicrobial activity, using an agar-well diffusion assay in microtiter plates, or antifungal activity using an agar-spot assay in 24-well plates. 504 Lactobacillus isolates were screened with minimal laboratory equipment and screening rates of 2000-5000 individual antimicrobial interactions.

Cloning and expression of synthetic genes encoding the broad antimicrobial spectrum bacteriocins SRCAM 602, OR-7, E-760, and L-1077, by recombinant Pichia pastoris

We have evaluated the cloning and functional expression of previously described broad antimicrobial spectrum bacteriocins SRCAM 602, OR-7, E-760, and L-1077, by recombinant Pichia pastoris. Synthetic genes, matching the codon usage of P. pastoris, were designed from the known mature amino acid sequence of these bacteriocins and cloned into the protein expression vector pPICZαA. The recombinant derived plasmids were linearized and transformed into competent P. pastoris X-33, and the presence of integrated plasmids into the transformed cells was confirmed by PCR and sequencing of the inserts. The antimicrobial activity, expected in supernatants of the recombinant P. pastoris producers, was purified using a multistep chromatographic procedure including ammonium sulfate precipitation, desalting by gel filtration, cation exchange-, hydrophobic interaction-, and reverse phase-chromatography (RP-FPLC). However, a measurable antimicrobial activity was only detected after the hydrophobic interaction and RP-FPLC steps of the purified supernatants. MALDI-TOF MS analysis of the antimicrobial fractions eluted from RP-FPLC revealed the existence of peptide fragments of lower and higher molecular mass than expected. MALDI-TOF/TOF MS analysis of selected peptides from eluted RP-FPLC samples with antimicrobial activity indicated the presence of peptide fragments not related to the amino acid sequence of the cloned bacteriocins.

Plantaricin LD1: a bacteriocin produced by food isolate of Lactobacillus plantarum LD1

Plantaricin LD1, a bacteriocin produced by Lactobacillus plantarum LD1, was characterized for biochemical and antimicrobial properties. Bacteriocin showed stability at high temperatures (100 °C for 20 min and 121 °C for 15 min under 15 psi pressure), in a pH range of 2.0-8.0 and also in the presence of organic solvents, surfactants and detergents. The crude preparation was not affected by catalase, amylase and lipase but activity was reduced in the presence of pepsin, trypsin and proteinase K showing proteinaceous nature of the compound. The molecular weight of bacteriocin was found to be ∼6.5 kDa, and antimicrobial activity was confirmed by bioassay. It inhibited not only related strains but also other Gram-positive and Gram-negative bacteria such as Lactobacillus curvatus NRRL B-4562, Lactococcus lactis subsp. lactis NRRL B-1821, Enterococcus faecium NRRL B-2354, Enterobacter cloacae NRRL B-14298, Micrococcus luteus, Staphylococcus aureus, urogenic Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Shigella flexneri and Vibrio sp. These properties of plantaricin LD1 suggest its applications not only in food safety but in therapeutics as well.