Capsular exopolysaccharide biosynthesis gene of Propionibacterium freudenreichii subsp. shermanii

Specificity Influences in (1→3)-β-d-Glucan-Supported Diagnosis of Invasive Fungal Disease

(1→3)-β-glucan (BDG) testing as an adjunct in the diagnosis of invasive fungal disease (IFD) has been in use for nearly three decades. While BDG has a very high negative predictive value in this setting, diagnostic false positives may occur, limiting specificity and positive predictive value. Although results may be diagnostically false positive, they are analytically correct, due to the presence of BDG in the circulation. This review surveys the non-IFD causes of elevated circulating BDG. These are in the main, iatrogenic patient contamination through the use of BDG-containing medical devices and parenterally-delivered materials as well as translocation of intestinal luminal BDG due to mucosal barrier injury. Additionally, infection with Nocardia sp. may also contribute to elevated circulating BDG. Knowledge of the factors which may contribute to such non-IFD-related test results can improve the planning and interpretation of BDG assays and permit investigational strategies, such as serial sampling and BDG clearance evaluation, to assess the likelihood of contamination and improve patient care.

Surface properties associated with the production of polysaccharides in the food bacteria Propionibacterium freudenreichii

This study explores the production of polysaccharides (PS) in the strain Pf2289 of the food species Propionibacterium freudenreichii. Pf2289 presents characteristics atypical of the species: a molar-shaped morphotype upon plating, and cells strongly aggregative in liquid medium. When plating Pf2289, another morphotype was observed with a 4% frequency of appearance: round-shaped colonies, typical of the species. A clone was isolated, designated Pf456. No reversibility of Pf456 towards the molar-shaped morphotype was observed. Pf2289 was shown to produce a surface polysaccharide (PS) bound to the cell wall, mainly during the stationary growth phase. Meanwhile, Pf456 had lost the ability to produce the PS. AFM images of Pf2289 showed that entangled filaments spread over the whole surface of the bacteria, whereas Pf456 exhibited a smooth surface. Adhesion force maps, performed with concanavalin-A grafted probes, revealed twice as much adhesion of Pf2289 to concanavalin-A compared to Pf456. Furthermore, the length of PS molecules surrounding Pf2289 measured at least 7 μm, whereas it only reached 1 μm in Pf456. Finally, the presence of PS had a strong impact on adhesion properties: Pf2289 did not adhere to hydrophobic surfaces, whereas Pf456 showed strong adhesion.

Characterization of Pediococcus ethanolidurans CUPV141: A β-D-glucan- and Heteropolysaccharide-Producing Bacterium

Pediococcus ethanolidurans CUPV141 is an exopolysaccharide (EPS)-producing lactic acid bacterium, first isolated from Basque Country cider (Spain). Physicochemical analysis of the EPS synthesized by the bacterium revealed that CUPV141 produces mostly a homopolysaccharide (HoPS), characterized as a 2-substituted (1,3)-β-D-glucan, together with a small quantity of a heteropolysaccharide (HePS) composed of glucose, galactose, glucosamine, and glycerol-3-phosphate, this being the first Pediococcus strain described to produce this kind of polymer. On the contrary, an isogenic strain CUPV141NR, generated by chemical mutagenesis of CUPV141, produced the HePS as the main extracellular polysaccharide and a barely detectable amount of 2-substituted (1,3)-β-D-glucan. This HoPS is synthesized by the transmembrane GTF glycosyltransferase (GTF), encoded by the gtf gene, which has been previously reported to be located in the pPP2 plasmid of the Pediococcus parvulus 2.6 strain. Southern blot hybridization revealed that in CUPV141 the gtf gene is located in a plasmid designated as pPE3, whose molecular mass (34.4 kbp) is different from that of pPP2 (24.5 kbp). Analysis of the influence of the EPS on the ability of the producing bacteria to adhere to the eukaryotic Caco-2 cells revealed higher affinity for the human enterocytes of CUPV141NR compared to that of CUPV141. This result indicates that, in contrast to the 2.6 strain, the presence of the HoPS does not potentiate the binding ability of P. ethanolidurans. Moreover, it supports that the phosphate-containing bacterial HePS improved the interaction between P. ethanolidurans and the eukaryotic cells.

EPS production by Propionibacterium freudenreichii facilitates its immobilization for propionic acid production

AIMS

Immobilization of microbial cells is a useful strategy for developing high cell density bioreactors with improved stability and productivity for production of different chemicals. Functionalization of the immobilization matrix or biofilm forming property of some strains has been utilized for achieving cell attachment. The aim of the present study was to investigate the production of exopolysaccharide (EPS) by Propionibacterium freudenreichii C.I.P 59.32 and utilize this feature for immobilization of the cells on porous glass beads for production of propionic acid.

METHODS AND RESULTS

Propionibacterium freudenreichii was shown to produce both capsular and excreted EPS during batch cultivations using glucose as carbon source. Different electron microscopy techniques confirmed the secretion of EPS and formation of cellular aggregates. The excreted EPS was mainly composed of mannose and glucose in a 5·3 : 1 g g^-1 ratio. Immobilization of the cells on untreated and polyethyleneimine (PEI)-treated Poraver beads in a bioreactor was evaluated. Higher productivity and yield of propionic acid (0·566 g l^-1  h^-1 and 0·314 g g^-1 , respectively) was achieved using cells immobilized to untreated beads and EPS production reached 617·5 mg l^-1 after 48 h.

CONCLUSION

These results suggest an important role of EPS-producing strains for improving cell immobilization and propionic acid production.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the EPS-producing microbe to be easily immobilized on a solid matrix and to be used in a bioprocess. Such a system could be optimized for achieving high cell density in fermentations without the need for functionalization of the matrix.

Identification of proteins involved in the anti-inflammatory properties of Propionibacterium freudenreichii by means of a multi-strain study

Propionibacterium freudenreichii, a dairy starter, can reach a population of almost 10⁹ propionibacteria per gram in Swiss-type cheese at the time of consumption. Also consumed as a probiotic, it displays strain-dependent anti-inflammatory properties mediated by surface proteins that induce IL-10 in leukocytes. We selected 23 strains with varied anti-inflammatory potentials in order to identify the protein(s) involved. After comparative genomic analysis, 12 of these strains were further analysed by surface proteomics, eight of them being further submitted to transcriptomics. The omics data were then correlated to the anti-inflammatory potential evaluated by IL-10 induction. This comparative omics strategy highlighted candidate genes that were further subjected to gene-inactivation validation. This validation confirmed the contribution of surface proteins, including SlpB and SlpE, two proteins with SLH domains known to mediate non-covalent anchorage to the cell-wall. Interestingly, HsdM3, predicted as cytoplasmic and involved in DNA modification, was shown to contribute to anti-inflammatory activity. Finally, we demonstrated that a single protein cannot explain the anti-inflammatory properties of a strain. These properties therefore result from different combinations of surface and cytoplasmic proteins, depending on the strain. Our enhanced understanding of the molecular bases for immunomodulation will enable the relevant screening for bacterial resources with anti-inflammatory properties.

Eradication and Sensitization of Methicillin Resistant Staphylococcus aureus to Methicillin with Bioactive Extracts of Berry Pomace

The therapeutic roles of phenolic blueberry (Vaccinium corymbosum) and blackberry (Rubus fruticosus) pomace (commercial byproduct) extracts (BPE) and their mechanism of actions were evaluated against methicillin resistant Staphylococcus aureus (MRSA). Five major phenolic acids of BPE, e.g., protocatechuic, p. coumaric, vanillic, caffeic, and gallic acids, as well as crude BPE completely inhibited the growth of vegetative MRSA in vitro while BPE+methicillin significantly reduced MRSA biofilm formation on plastic surface. In addition, BPE restored the effectiveness of methicillin against MRSA by down-regulating the expression of methicillin resistance (mecA) and efflux pump (norA, norB, norC, mdeA, sdrM, and sepA) genes. Antibiogram with broth microdilution method showed that MIC of methicillin reduced from 512 μg/mL to 4 μg/mL when combined with only 200 μg Gallic Acid Equivalent (GAE)/mL of BPE. Significant reduction in MRSA adherence to and invasion into human skin keratinocyte Hek001 cells were also noticed in the presence of BPE. BPE induced anti-apoptosis and anti-autophagy pathways through overexpression of Bcl-2 gene and down-regulation of TRADD and Bax genes (inducers of apoptosis pathway) in Hek001 cells. In summary, novel and sustainable prophylactic therapy can be developed with BPE in combination with currently available antibiotics, especially methicillin, against skin and soft tissue infections with MRSA.

Research on some factors influencing acid and exopolysaccharide produced by dairy propionibacterium strains isolated from traditional homemade Turkish cheeses

In this study, a total of 32 isolated strains and 5 reference strains of dairy propionibacteria were analyzed for acid and exopolysaccharide (EPS) production in skim milk and yeast extract-lactate broth (YEL) media in order to investigate the physiological background and preservative role of acid and EPS. The effects of final culture pH and optical density on acid and EPS production were also determined. On average, all strains produced more acid and reached lower final pH values in skim milk than in YEL medium. While the correlations obtained between the acid produced by propionibacterium strains and their final culture pH in skim milk medium were significant (P < 0.01), no correlations were found between optical density, final pH, and produced acid in YEL medium. Sixteen isolated and five reference strains of propionibacteria were tested further for the ability to produce propionic and acetic acids. On average, Propionibacterium freudenreichii subsp. shermanii and P. freudenreichii subsp. freudenreichii strains produced higher amounts of propionic and acetic acids than did Propionibacterium jensenii in YEL medium. The acid produced by these strains may be used as a preservative in the food industry for replacement or reduction of the increasing use of chemical additives. The EPS production by propionibacterium strains during growth in YEL medium was 72 to 168 mg/liter, while in skim milk it was 94 to 359 mg/liter. The monomer compositions of the EPSs formed by the six selected dairy propionibacteria strains were analyzed. The EPSs may have applications as food grade additives and viscosity-stabilizing agents.

Investigating hydrophobicity and the effect of exopolysaccharide on aggregation properties of dairy propionibacteria isolated from Turkish homemade cheeses

Propionic acid bacteria have been used widely as starter cultures. However, their potential as probiotics has received little attention. The ability to auto- and coaggregate is a desirable property for probiotics in health-promoting foods. Therefore, in the current study, we assessed the effect of exopolysaccharides produced by dairy propionibacteria strains on the aggregative and hydrophobicity properties. All propionibacteria strains tested showed auto- and coaggregation ability with Escherichia coli ATCC 11229, but the results were strain specific and dependent on exopolysaccharides production and incubation conditions. In addition, propionibacteria strains tested were determined to be highly hydrophilic. Our results indicate that the ability to autoaggregate, together with cell-surface hydrophobicity and coaggregation abilities with an E. coli strain, can be used for preliminary screening in order to identify potentially probiotic bacteria suitable for human or animal use.

Contribution of surface β-glucan polysaccharide to physicochemical and immunomodulatory properties of Propionibacterium freudenreichii

Propionibacterium freudenreichii is a bacterial species found in Swiss-type cheeses and is also considered for its health properties. The main claimed effect is the bifidogenic property. Some strains were shown recently to display other interesting probiotic potentialities such as anti-inflammatory properties. About 30% of strains were shown to produce a surface exopolysaccharide (EPS) composed of (1→3,1→2)-β-D-glucan due to a single gene named gtfF. We hypothesized that functional properties of P. freudenreichii strains, including their anti-inflammatory properties, could be linked to the presence of β-glucan. To evaluate this hypothesis, gtfF genes of three β-glucan-producing strains were disrupted. These knockout (KO) mutants were complemented with a plasmid harboring gtfF (KO-C mutants). The absence of β-glucan in KO mutants was verified by immunological detection and transmission electron microscopy. We observed by atomic force microscopy that the absence of β-glucan in the KO mutant dramatically changed the cell's topography. The capacity to adhere to polystyrene surface was increased for the KO mutants compared to wild-type (WT) strains. Anti-inflammatory properties of WT strains and mutants were analyzed by stimulation of human peripheral blood mononuclear cells (PBMCs). A significant increase of the anti-inflammatory interleukin-10 cytokine production by PBMCs was measured in the KO mutants compared to WT strains. For one strain, the role of β-glucan in mice gut persistence was assessed, and no significant difference was observed between the WT strain and its KO mutant. Thus, β-glucan appears to partly hide the anti-inflammatory properties of P. freudenreichii; which is an important result for the selection of probiotic strains.

Naturally occurring 2-substituted (1,3)-beta-D-glucan producing Lactobacillus suebicus and Pediococcus parvulus strains with potential utility in the production of functional foods

We have isolated three lactic acid bacteria (Lactobacillus suebicus CUPV221, Pediococcus parvulus CUPV1 and P. parvulus CUPV22) that produced high levels of 2-substituted (1,3)-beta-D-glucans which increased the viscosity of the growth media. The (1,3)-beta-D-glucan consisted of two main molecular species, with masses of approximately 10(7) and 10(4) Da, whose proportions varied among the strains. The three strains survived exposure to saliva and simulated gastric conditions at pH 5, with P. parvulus CUPV22 surviving at pH 3.1, and L. suebicus CUPV221 surviving at pH 1.8. All strains were resistant to pancreatin and bile salts. P. parvulus CUPV22 exhibited the highest adhesion (10.5%) to Caco-2 cells, which decreased to 1.2% after washing the cells. Finally, P. parvulus CUPV22 and L. suebicus CUPV221 induced the production of inflammation-related cytokines by polarized macrophages, and interestingly, L. suebicus stimulated the production of cytokine IL-10. These results indicate that the three strains have potential utility for the production of functional foods.

The complete genome of Propionibacterium freudenreichii CIRM-BIA1, a hardy actinobacterium with food and probiotic applications

BACKGROUND

Propionibacterium freudenreichii is essential as a ripening culture in Swiss-type cheeses and is also considered for its probiotic use. This species exhibits slow growth, low nutritional requirements, and hardiness in many habitats. It belongs to the taxonomic group of dairy propionibacteria, in contrast to the cutaneous species P. acnes. The genome of the type strain, P. freudenreichii subsp. shermanii CIRM-BIA1 (CIP 103027(T)), was sequenced with an 11-fold coverage.

METHODOLOGY/PRINCIPAL FINDINGS

The circular chromosome of 2.7 Mb of the CIRM-BIA1 strain has a GC-content of 67% and contains 22 different insertion sequences (3.5% of the genome in base pairs). Using a proteomic approach, 490 of the 2439 predicted proteins were confirmed. The annotation revealed the genetic basis for the hardiness of P. freudenreichii, as the bacterium possesses a complete enzymatic arsenal for de novo biosynthesis of aminoacids and vitamins (except panthotenate and biotin) as well as sequences involved in metabolism of various carbon sources, immunity against phages, duplicated chaperone genes and, interestingly, genes involved in the management of polyphosphate, glycogen and trehalose storage. The complete biosynthesis pathway for a bifidogenic compound is described, as well as a high number of surface proteins involved in interactions with the host and present in other probiotic bacteria. By comparative genomics, no pathogenicity factors found in P. acnes or in other pathogenic microbial species were identified in P. freudenreichii, which is consistent with the Generally Recognized As Safe and Qualified Presumption of Safety status of P. freudenreichii. Various pathways for formation of cheese flavor compounds were identified: the Wood-Werkman cycle for propionic acid formation, amino acid degradation pathways resulting in the formation of volatile branched chain fatty acids, and esterases involved in the formation of free fatty acids and esters.

CONCLUSIONS/SIGNIFICANCE

With the exception of its ability to degrade lactose, P. freudenreichii seems poorly adapted to dairy niches. This genome annotation opens up new prospects for the understanding of the P. freudenreichii probiotic activity.

Correlation of the capsular phenotype in Propionibacterium freudenreichii with the level of expression of gtf, a unique polysaccharide synthase-encoding gene

Many food-grade bacteria produce exopolysaccharides (EPS) that affect the texture of fermented food products and that may be involved in probiotic properties. Propionibacterium freudenreichii is a Gram-positive food-grade bacterium with reported probiotic capabilities that is widely used as starter in Swiss-type cheese. In this study, 68 strains of P. freudenreichii were screened for the beta-glucan capsular phenotype by immunoagglutination with a specific antibody and for the presence of the gtf gene coding for polysaccharide synthase. All strains were positive for PCR amplification with gtf gene-specific primers, but the presence of beta-glucan capsular EPS was detected for only 35% of the strains studied. Disruption of gtf in P. freudenreichii revealed that gtf is a unique gene involved in beta-glucan capsular EPS production in P. freudenreichii. The gtf gene was transferred into and expressed in Lactococcus lactis, in which it conferred an agglutination-positive phenotype. Expression of the gtf gene was measured by performing quantitative reverse transcription-PCR assays with RNA from four capsular and three noncapsular strains. A positive correlation was found between the beta-glucan capsular phenotype and gtf gene expression. Sequencing of the region upstream of the gtf open reading frame revealed the presence of an insertion element (IS element) in this upstream region in the four strains with the beta-glucan capsular phenotype. The role of the IS element in the expression of neighboring genes and its impact on interstrain variability of the P. freudenreichii capsule phenotype remain to be elucidated.