Jelena Lozo

Characterization and antimicrobial activity of bacteriocin 217 produced by natural isolate Lactobacillus paracasei subsp. paracasei BGBUK2-16.

The strain Lactobacillus paracasei subsp. paracasei BGBUK2-16. which was isolated from traditionally homemade white-pickled cheese, produces bacteriocin 217 (Bac217; approximately 7 kDa). The onset of Bac217 biosynthesis was observed in the logarithmic phase of growth, and the production plateau was reached after 9 or 12 h of incubation at 37 and 30 degrees C, respectively, when culture entered the early stationary phase. Biochemical characterization showed that Bac217 retained antimicrobial activity within the range of pH 3 to 12 or after treatment at 100 degrees C for 15 min. Bac217 antimicrobial activity also remained unchanged after storage at 4 degrees C for 6 months or -20 degrees C for up to 12 months. However, Bac217 activity was completely lost after treatment with different proteolytic enzymes. BGBUK2-16 contains only one plasmid about 80 kb in size. Plasmid curing indicated that genes coding for Bac217 synthesis and immunity seem to be located on this plasmid. Bac217 exhibited antimicrobial activity against some pathogenic bacteria, such as Staphylococcus aureus and Bacillus cereus. Interestingly, Bac217 showed activity against Salmonella sp. and Pseudomonas aeruginosa ATCC27853. The inhibitory effect of BGBUK2-16 on the growth of S. aureus in mixed culture was observed. S. aureus treatment with Bac217 led to a considerable decrease (CFU/ml) within a short period of time. The mode of Bac217 action on S. aureus was identified as bactericidal. It should be noted that the strain BGBUK2-16 was shown to be resistant to bacteriocin nisin, which is otherwise widely used as a food additive for fermented dairy products.

Preliminary characterization of lactic acid bacteria isolated from Zlatar cheese

Aims:  Isolation, characterization and identification of lactic acid bacteria (LAB) from artisanal Zlatar cheese during the ripening process and selection of strains with good technological characteristics.

A Zn-Dependent Metallopeptidase Is Responsible for Sensitivity to LsbB, a Class II Leaderless Bacteriocin of Lactococcus lactis subsp. lactis BGMN1-5

Lactococcus lactis subsp. lactis BGMN1-5 produces a leaderless class II bacteriocin called LsbB. To identify the receptor for LsbB, a cosmid library of the LsbB-sensitive strain BGMN1-596 was constructed. About 150 cosmid clones were individually isolated and transferred to LsbB-resistant mutants of BGMN1-596. Cosmid pAZILcos/MN2, carrying a 40-kb insert, was found to restore LsbB sensitivity in LsbB-resistant mutants. Further subcloning revealed that a 1.9-kb fragment, containing only one open reading frame, was sufficient to restore sensitivity. The fragment contains the gene yvjB coding for a Zn-dependent membrane-bound metallopeptidase, suggesting that this gene may serve as the receptor for LsbB. Further support for this notion derives from several independent experiments: (i) whole-genome sequencing confirmed that all LsbB-resistant mutants contain mutations in yvjB; (ii) disruption of yvjB by direct gene knockout rendered sensitive strains BGMN1-596 and IL1403 resistant to LsbB; and (iii) most compellingly, heterologous expression of yvjB in naturally resistant strains of other species, such as Lactobacillus paracasei and Enterococcus faecalis, also rendered them sensitive to the bacteriocin. To our knowledge, this is the first time a membrane-bound peptidase gene has been shown to be involved in bacteriocin sensitivity in target cells. We also demonstrated a novel successful approach for identifying bacteriocin receptors.

Molecular Characterization of a Novel Bacteriocin and an Unusually Large Aggregation Factor of Lactobacillus paracasei subsp. paracasei BGSJ2-8, a Natural Isolate from Homemade Cheese

Screening the collection of natural isolates from semi-hard homemade cheese resulted in isolation and characterization of strain Lactobacillus paracasei subsp. paracasei BGSJ2-8. The strain BGSJ2-8 harbors several important phenotypes, such as bacteriocin production, aggregation phenomenon, and production of proteinase. Bacteriocin SJ was purified by three-step chromatography. Mass spectrometry established molecular mass of the active peptide at 5372 Da. The auto-aggregation phenotype of wild-type (WT) strain was mediated by secreted aggregation-promoting factor (protein of molecular mass > 200 kDa), probably acting in cooperation with other cell surface protein(s). Comparative study of WT and its spontaneous nonaggregating derivative revealed that aggregation factor was responsible for the observed differences in the bacteriocin and proteinase activities. Bacteriocin SJ activity and resistance to different stresses were higher in the presence of aggregating factor. In contrast, proteinase activity was stronger in the nonaggregating derivative.

Cloning and expression of a novel lactococcal aggregation factor from Lactococcus lactis subsp. lactis BGKP1

BackgroundAggregation may play a main role in the adhesion of bacteria to the gastrointestinal epithelium and their colonization ability, as well as in probiotic effects through co-aggregation with intestinal pathogens and their subsequent removal. The aggregation phenomenon in lactococci is directly associated with the sex factor and lactose plasmid co-integration event or duplication of the cell wall spanning (CWS) domain of PrtP proteinase.ResultsLactococcus lactis subsp. lactis BGKP1 was isolated from artisanal semi-hard homemade cheese and selected due to its strong auto-aggregation phenotype. Subsequently, non-aggregating derivative (Agg-) of BGKP1, designated as BGKP1-20, was isolated, too. Comparative analysis of cell surface proteins of BGKP1 and derivative BGKP1-20 revealed a protein of approximately 200 kDa only in the parental strain BGKP1. The gene involved in aggregation (aggL) was mapped on plasmid pKP1 (16.2 kb), cloned and expressed in homologous and heterologous lactococci and enterococci. This novel lactococcal aggregation protein was shown to be sufficient for cell aggregation in all tested hosts. In addition to the aggL gene, six more ORFs involved in replication (repB and repX), restriction and modification (hsdS), transposition (tnp) and possible interaction with mucin (mbpL) were also located on plasmid pKP1.ConclusionAggL is a new protein belonging to the collagen-binding superfamily of proteins and is sufficient for cell aggregation in lactococci.

Technological and probiotic potential of BGRA43 a natural isolate of Lactobacillus helveticus

Lactobacillus helveticus BGRA43 is a human intestinal isolate showing antimicrobial activity, amongst others, against Yersinia enterocolitica, Shigella sonnei, Shigella flexneri, and Streptococcus pneumoniae. BGRA43 produces PrtH proteinase with proteolytic activity on both casein and β-lactoglobulin (BLG). BGRA43 is able to reduce the allergenicity of BLG. Bioactive peptides released in BGRA43 fermented milk are potent modulators of innate immunity by modulating the production of proinflammatory cytokines IL-6 and TNF-α. BGRA43 is able to survive in simulated gastric and intestinal conditions. The growth of BGRA43 in milk results in a fast acidification lowering the milk pH to 4.53 generating mild, homogeneous, and viscous yogurt-like product. The strain BGRA43 grows suitably in pure cow or goat’s milk as well as in milk containing inulin or nutrim even when they are used as the sole carbon source. It is suggested that strain BGRA43 could be used as a single-strain culture for the preparation of yogurt-like products from bovine or caprine milk. Overall, L. helveticus BGRA43 could be considered as a potential probiotic candidate with appropriate technological properties attractive for the dairy industry.

Construction of a new shuttle vector and its use for cloning and expression of two plasmid-encoded bacteriocins from Lactobacillus paracasei subsp. paracasei BGSJ2-8.

A new shuttle-cloning vector, pA13, was constructed and successfully introduced into Escherichia coli, Lactobacillus and Lactococcus strains. It showed high segregational and structural stability in all three hosts. The natural plasmid pSJ2-8 from L. paracasei subsp. paracasei BGSJ2-8 was cloned into pA13 using BamHI to obtain the construct, pB5. Sequencing and in silico analysis of pB5 revealed fifteen open reading frames (ORF). Plasmid pSJ2-8 harbours genes encoding the production of two bacteriocins, BacSJ and acidocin 8912. Combined N-terminal amino acid sequencing of BacSJ in combination with DNA sequencing of the bacSJ2-8 gene enabled determination of the primary structure of bacteriocin BacSJ. The bacSJ2-8 gene encodes 68-amino-acid peptide with a double-glycine leader peptide consisting of 18 amino acids, followed by the orf2 (bacSJ2-8i) which encodes the immunity protein of BacSJ. The production and functional expression of BacSJ in homologous and heterologous hosts suggest that bacSJ2-8 and bacSJ2-8i together with the genes encoding the ABC transporter and accessory protein are the minimal requirements for production of BacSJ. Biochemical and genetic analyses showed that BacSJ belongs to class II bacteriocins.

Expression of bacteriocin LsbB is dependent on a transcription terminator.

The production of LsbB, leaderless class II bacteriocin, is encoded by genes (lsbB and lmrB) located on plasmid pMN5 in Lactococcus lactis BGMN1-5. Heterologous expression of the lsbB gene using the pAZIL vector (pAZIL-lsbB) in L. lactis subsp. cremoris MG7284 resulted in a significant reduction (more than 30 times) of bacteriocin LsbB expression. Subcloning and deletion experiments with plasmid pMN5 revealed that full expression of LsbB requires the presence of a complete transcription terminator located downstream of the lsbB gene. RNA stability analysis revealed that the presence of a transcription terminator increased the RNA stability by three times and the expression of LsbB by 30 times. The study of the influence of transcription terminator on the expression of other bacteriocin genes (lcnB, for lactococcin B production) indicated that this translational terminator likely functions in a lsbB-specific manner rather than in a general manner.

Licheniocin 50.2 and Bacteriocins from Lactococcus lactis subsp. lactis biovar. diacetylactis BGBU1-4 Inhibit Biofilms of Coagulase Negative Staphylococci and Listeria monocytogenes Clinical Isolates.

Background Coagulase negative staphylococci (CoNS) and Listeria monocytogenes have important roles in pathogenesis of various genital tract infections and fatal foetomaternal infections, respectively. The aim of our study was to investigate the inhibitory effects of two novel bacteriocins on biofilms of CoNS and L. monocytogenes genital isolates. Methods The effects of licheniocin 50.2 from Bacillus licheniformis VPS50.2 and crude extract of bacteriocins produced by Lactococcus lactis subsp. lactis biovar. diacetylactis BGBU1-4 (BGBU1-4 crude extract) were evaluated on biofilm formation and formed biofilms of eight CoNS (four S. epidermidis, two S. hominis, one S. lugdunensis and one S. haemolyticus) and 12 L. monocytogenes genital isolates. Results Licheniocin 50.2 and BGBU1-4 crude extract inhibited the growth of both CoNS and L. monocytogenes isolates, with MIC values in the range between 200–400 AU/ml for licheniocin 50.2 and 400–3200 AU/ml for BGBU1-4 crude extract. Subinhibitory concentrations (1/2 × and 1/4 × MIC) of licheniocin 50.2 inhibited biofilm formation by all CoNS isolates (p < 0.05, respectively), while BGBU1-4 crude extract inhibited biofilm formation by all L. monocytogenes isolates (p < 0.01 and p < 0.05, respectively). Both bacteriocins in concentrations of 100 AU/mL and 200 AU/mL reduced the amount of 24 h old CoNS and L. monocytogenes biofilms (p < 0.05, p < 0.01, p < 0.001). Conclusions This study suggests that novel bacteriocins have potential to be used for genital application, to prevent biofilm formation and/or to eradicate formed biofilms, and consequently reduce genital and neonatal infections by CoNS and L. monocytogenes.

Novel antilisterial bacteriocin licheniocin 50.2 from Bacillus licheniformis VPS50.2 isolated from soil sample.

To isolate and characterize bacteriocin, licheniocin 50.2, from soil bacteria identified as Bacillus licheniformis.