Evaluating the individual effects of temperature and salt on table olive related microorganisms

Statistical modelling techniques were used in the present study to assess the individual effects of temperature and NaCl concentration on the growth of 10 lactic acid bacteria and 6 yeast strains mostly isolated from different forms of table olive processing and belonging to the species Lactobacillus pentosus, Lactobacillus plantarum, Saccharomyces cerevisiae, Wickerhamomyces anomalus and Candida boidinii. The mathematical models obtained in synthetic laboratory media show that yeasts, except for C. boidinii, were more resistant to a high salt concentration than lactic acid bacteria, with an MIC value ranging from 163.5 (S. cerevisiae) to 166.9 g/L (W. anomalus); while for L. pentosus and L. plantarum this parameter ranged from 110.6 to 117.6 g/L, respectively. With regards to temperature, lactic acid bacteria showed a slight trend towards supporting higher temperature values than yeasts, with the exception of S. cerevisiae. The maximum temperatures for growth of L. pentosus and L. plantarum were 41.9 and 43.0 °C, respectively; while for W. anomalus and C. boidinii they were 38.2 and 36.5 °C. The optimum temperatures for growth were also higher for L. pentosus and L. plantarum (35.5 and 32.9 °C), compared to W. anomalus and C. boidinii (29.3 and 26.9 °C, respectively). Additional experiments carried out in natural olive brines confirmed previous results, showing that high NaCl concentrations clearly favoured yeast growth and that at high temperatures LAB slightly overcame yeasts. Results obtained in this paper could be useful for industry for a better control of both table olive fermentation and packaging.

Yeasts in table olive processing: desirable or spoilage microorganisms?

Yeasts are unicellular eukaryotic microorganisms isolated from many foods, and are commonly found in table olive processing where they can play a double role. On one hand, these microorganisms can produce spoilage of fruits due to the production of bad odours and flavours, the accumulation of CO(2) leading to swollen containers, the clouding of brines, the softening of fruits and the degradation of lactic acid, which is especially harmful during table olive storage and packaging. But on the other hand, fortunately, yeasts also possess desirable biochemical activities (lipase, esterase, β-glucosidase, catalase, production of killer factors, etc.) with important technological applications in this fermented vegetable. Recently, the probiotic potential of olive yeasts has begun to be evaluated because many species are able to resist the passage through the gastrointestinal tract and show beneficial effects on the host. In this way, yeasts may improve consumers' health by decreasing cholesterol levels, inhibiting pathogens, degrading non assimilated compounds, producing antioxidants and vitamins, adhering to intestinal cells or by maintaining epithelial barrier integrity. Many yeast species, usually also found in table olive processing, such as Wicherhamomyces anomalus, Saccharomyces cerevisiae, Pichia membranifaciens and Kluyveromyces lactis, have been reported to exhibit some of these properties. Thus, the selection of the most appropriate strains to be used as starters, alone or in combination with lactic acid bacteria, is a promising research line to develop in a near future which might improve the added value of the commercialized product.

Formation of lactic acid bacteria-yeasts communities on the olive surface during Spanish-style Manzanilla fermentations

This work examines the formation of poly-microbial communities adhered to the surface of Manzanilla olive fruits processed according to the Spanish style. The experimental design consisted of four pilot fermenters inoculated with four Lactobacillus pentosus strains, plus another fermenter which was not inoculated and fermented spontaneously. Lactic acid bacteria and yeasts were analysed in depth on olive epidermis throughout fermentation by plate count, molecular techniques and scanning electron microscopy. Data show that in all cases high population levels (above 8 log(10) CFU per olive) were reached for both groups of microorganisms at the second week of fermentation and that these counts never fell below 6 log(10) CFU per olive during the 3 months that fermenters were monitored. In situ observation of olive epidermis slices revealed a strong aggregation and adhesion between bacteria and yeasts by the formation of a matrix which embedded the microorganisms. Geotrichum candidum, Pichia galeiformis and Candida sorbosa were the main yeast species isolated from these biofilms at the end of fermentation (confirmed by RFLP analysis of the 5.8S-ITS region), while molecular characterization of lactobacilli isolates by means of RAPD-PCR with primer OPL(5) showed in many cases a high similarity in their banding profiles with the inoculated strains. Results obtained in this survey show the importance of studying the olive epidermis throughout fermentation, because ultimately, olives are ingested by consumers.

Use of Lactobacillus plantarum LPCO10, a Bacteriocin Producer, as a Starter Culture in Spanish-Style Green Olive Fermentations

Bacteriocin-producing Lactobacillus plantarum LPCO10 and its non-bacteriocin-producing, bacteriocinimmune derivative, L. plantarum 55-1, were evaluated separately for growth and persistence in natural Spanish-style green olive fermentations. Both strains were genetically marked and selectively enumerated using antibiotic-containing media. Plasmid profile and bacteriocin production (bac) were used as additional markers. When olive brines were inoculated at 10 CFU/ml, the parent strain, LPCO10, proliferated to dominate the epiphytic microflora, sharing high population levels with other spontaneously occurring lactobacilli and persisting throughout the fermentation (12 weeks). In contrast, the derivative strain could not be isolated after 7 weeks. Stability of both plasmid profile and bac (LPCO10 strain) or bac (55-1 strain) phenotype was shown by L. plantarum LPCO10 and L. plantarum 55-1 isolated throughout the fermentation. Bacteriocin activity could be found in the L. plantarum LPCO10-inoculated brines only after ammonium sulfate precipitation and concentration (20 times) of the final brine. Spontaneously occurring lactobacilli and lactic coccus populations, which were isolated from each of the fermenting brines studied during this investigation, were shown to be sensitive to the bacteriocins produced by L. plantarum LPCO10 when tested by the drop diffusion test. The declines in both pH and glucose levels throughout the fermentative process were similar in L. plantarum LPCO10- and in L. plantarum 55-1-inoculated brines and were comparable to the declines in the uninoculated brines. However, the final concentration of lactic acid in L. plantarum LPCO10-inoculated brines was higher than in the L. plantarum 55-1-inoculated brines and uninoculated brines. These results indicated that L. plantarum LPCO10 may be useful as a starter culture to control the lactic acid fermentation of Spanish-style green olives.

Optimization of bacteriocin production by batch fermentation of Lactobacillus plantarum LPCO10

Optimization of bacteriocin production by Lactobacillus plantarum LPCO10 was explored by an integral statistical approach. In a prospective series of experiments, glucose and NaCl concentrations in the culture medium, inoculum size, aeration of the culture, and growth temperature were statistically combined using an experimental 2(3)(5-2) fractional factorial two-level design and tested for their influence on maximal bacteriocin production by L. plantarum LPCO10. After the values for the less-influential variables were fixed, NaCl concentration, inoculum size, and temperature were selected to study their optimal relationship for maximal bacteriocin production. This was achieved by a new experimental 3(2)(3-1) fractional factorial three-level design which was subsequently used to build response surfaces and analyzed for both linear and quadratic effects. Results obtained indicated that the best conditions for bacteriocin production were shown with temperatures ranging from 22 to 27 degrees C, salt concentration from 2.3 to 2.5%, and L. plantarum LPCO10 inoculum size ranging from 10(7.3) to 10(7.4) CFU/ml, fixing the initial glucose concentration at 2%, with no aeration of the culture. Under these optimal conditions, about 3.2 x 10(4) times more bacteriocin per liter of culture medium was obtained than that used to initially purify plantaricin S from L. plantarum LPCO10 to homogeneity. These results indicated the importance of this study in obtaining maximal production of bacteriocins from L. plantarum LPCO10 so that bacteriocins can be used as preservatives in canned foods.

Partial characterization of a bacteriocin produced by Lactobacillus delbrueckii subsp. lactis UO004, an intestinal isolate with probiotic potential

AIMS

The partial characterization of a bacteriocin produced by a human Lactobacillus delbrueckii isolate with probiotic potential.

METHODS AND RESULTS

A bacterocin, UO004, was partially purified by cation exchange followed by a hydrophobic interaction column, biochemically characterized and the N-terminal region sequenced. Bacteriocin UO004 was found to be a hydrophobic, heat-stable polypeptide with an apparent molecular mass of 6 kDa. It was also stable and active over a wide pH range.

CONCLUSION

The active compound was proteinaceous, heat-stable, and had a bactericidal (and bacteriolytic) mode of action on a limited number of micro-organisms. Such a narrow spectrum of activity is typical for bacteriocins produced by intestinal Lactobacillus.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacteriocin UO004 from a probiotic strain is a new compound that does not share any homology with any other known lactic acid bacteria bacteriocin. Furthermore, Lact. delbrueckii is regarded as a suitable starter for the production of fermented milks.

Bacteriocin production in vancomycin-resistant and vancomycin-susceptible Enterococcus isolates of different origins

Bacteriocin production was determined for 218 Enterococcus isolates (Enterococcus faecalis [93] and E. faecium [125]) obtained from different origins (human clinical samples [87], human fecal samples [78], sewage [28], and chicken samples [25]) and showing different vancomycin susceptibility patterns (vancomycin resistant, all of them vanA positive [56], and vancomycin susceptible [162]). All enterococcal isolates were randomly selected except for the vancomycin-resistant ones. A total of 33 isolates of eight different bacterial genera were used as indicators for bacteriocin production. Forty-seven percent of the analyzed enterococcal isolates were bacteriocin producers (80.6% of E. faecalis and 21.6% of E. faecium isolates). The percentage of bacteriocin producers was higher among human clinical isolates (63.2%, 81.8% of vancomycin-resistant isolates and 60.5% of vancomycin-susceptible ones) than among isolates from the other origins (28 to 39.3%). Only one out of the 15 vancomycin-resistant isolates from human fecal samples was a bacteriocin producer, while 44.4% of fecal vancomycin-susceptible isolates were. The bacteriocin produced by the vanA-containing E. faecium strain RC714, named bacteriocin RC714, was further characterized. This bacteriocin activity was cotransferred together with the vanA genetic determinant to E. faecalis strain JH2-2. Bacteriocin RC714 was purified to homogeneity and its primary structure was determined by amino acid sequencing, showing an identity of 88% and a similarity of 92% with the previously described bacteriocin 31 from E. faecalis YI717. The presence of five different amino acids in bacteriocin RC714 suggest that this could be a new bacteriocin. The results obtained suggest that the epidemiology of vancomycin resistance may be influenced by different factors, including bacteriocin production.

Purification and genetic characterization of enterocin I from Enterococcus faecium 6T1a, a novel antilisterial plasmid-encoded bacteriocin which does not belong to the pediocin family of bacteriocins

Enterocin I (ENTI) is a novel bacteriocin produced by Enterococcus faecium 6T1a, a strain originally isolated from a Spanish-style green olive fermentation. The bacteriocin is active against many olive spoilage and food-borne gram-positive pathogenic bacteria, including clostridia, propionibacteria, and Listeria monocytogenes. ENTI was purified to homogeneity by ammonium sulfate precipitation, binding to an SP-Sepharose fast-flow column, and phenyl-Sepharose CL-4B and C2/C18 reverse-phase chromatography. The purification procedure resulted in a final yield of 954% and a 170,000-fold increase in specific activity. The primary structure of ENTI was determined by amino acid and nucleotide sequencing. ENTI consists of 44 amino acids and does not show significant sequence similarity with any other previously described bacteriocin. Sequencing of the entI structural gene, which is located on the 23-kb plasmid pEF1 of E. faecium 6T1a, revealed the absence of a leader peptide at the N-terminal region of the gene product. A second open reading frame, ORF2, located downstream of entI, encodes a putative protein that is 72.7% identical to ENTI. entI and ORF2 appear to be cotranscribed, yielding an mRNA of ca. 0.35 kb. A gene encoding immunity to ENTI was not identified. However, curing experiments demonstrated that both enterocin production and immunity are conferred by pEF1.

Bacteriocin production and competitiveness of Lactobacillus plantarum LPCO10 in olive juice broth, a culture medium obtained from olives

A culture medium, named olive juice broth, which resembles the natural environment of Lactobacillus plantarum in the traditional Spanish-style green olive fermentation was obtained from green olives. In this medium, the bacteriocin-producing L. plantarum LPCO10 strain was able to produce bacteriocin throughout the incubation time (15 days). Bacteriocin purification from olive juice broth was achieved by a protocol including ammonium sulphate precipitation of cell-free, L. plantarum LPCO10 culture supernatants, and cation-exchange, hydrophobic-interaction and reversed-phase chromatographies. In a series of mixed cultures in olive juice broth, L. plantarum LPCO10 was able to dominate the bacteriocin-sensitive L. plantarum 128/2 strain, whereas the non-bacteriocin-producing, LPCO10 strain derivative, L. plantarum 55-1 strain did not show such capability. These results indicated that olive juice broth may be a valuable experimental substitute for olive fermentation brine in gaining more knowledge about the role of the bacteriocin-producing L. plantarum strains in the control of the Spanish-style green olive fermentation.

Molecular analysis of the locus responsible for production of plantaricin S, a two-peptide bacteriocin produced by Lactobacillus plantarum LPCO10

A 4.5-kb region of chromosomal DNA carrying the locus responsible for the production of plantaricin S, a two-peptide bacteriocin produced by Lactobacillus plantarum LPCO10 (R. Jiménez-Díaz, J. L. Ruiz-Barba, D. P. Cathcart, H. Holo, I. F. Nes, K. H. Sletten, and P. J. Warner, Appl. Environ. Microbiol. 61:4459-4463, 1995), has been cloned, and the nucleotide sequence has been elucidated. Two genes, designated plsA and plsB and encoding peptides alpha and beta, respectively, of plantaricin S, plus an open reading frame (ORF), ORF2, were found to be organized in an operon. Northern blot analysis showed that these genes are cotranscribed, giving a ca. 0.7-kb mRNA, whose transcription start point was determined by primer extension. Nucleotide sequences of plsA and plsB revealed that both genes are translated as bacteriocin precursors which include N-terminal leader sequences of the double-glycine type. The role of ORF2 is unknown at the moment, although it might be expected to encode an immunity protein of the type described for other bacteriocin operons. In addition, several other potential ORFs have been found, including some which may be responsible for the regulation of bacteriocin production. Two of them, ORF8 and ORF14, show strong homology with histidine protein kinase and response regulator genes, respectively, which have been found to be involved in the regulation of the production of other bacteriocins from lactic acid bacteria. A third ORF, ORF5, shows homology with gene agrB from Staphylococcus aureus, which is involved in the mechanism of regulation of the virulence phenotype in this species. Thus, an agr-like regulatory system for the production of plantaricin S is postulated.

Purification and partial amino acid sequence of plantaricin S, a bacteriocin produced by Lactobacillus plantarum LPCO10, the activity of which depends on the complementary action of two peptides

Plantaricin S, one of the two bacteriocins produced by Lactobacillus plantarum LPCO10, which was isolated from a green-olive fermentation (R. Jiménez-Díaz, R.M. Ríos-Sánchez, M. Desmazeaud, J.L.Ruiz-Barba, and J.-C. Piard, Appl. Environ. Microbiol. 59:1416-1424, 1993), has been purified to homogeneity by ammonium sulfate precipitation, by binding to SP-Sepharose fast-flow, phenyl-Sepharose CL-4B, and C2/C18 reverse-phase chromatographies. The purification resulted in a final yield of 91.6% and a 352,617-fold increase in the specific activity. The bacteriocin activity was associated with two distinct peptides, termed alpha and beta, which were separated by C2/C18 reverse-phase chromatography. Although beta alone appeared to retain a trace of inhibitory activity, the complementary action of both the alpha and beta peptides was required for full bacteriocin activity, as judged by both the agar well diffusion and the microtiter plate assays. From the N-terminal end, 26 and 24 amino acids residues of alpha and beta, respectively, were sequenced. Further attempts at sequencing revealed no additional amino acids residues, suggesting that either modifications in the next amino acid residue blocked the sequencing region or that the C-terminal end had been reached. The amino acid sequences of alpha and beta show no apparent homology to each or to other bacteriocins purified from lactic acid bacteria.

Vitamin and amino acid requirements of Lactobacillus plantarum strains isolated from green olive fermentations

The requirement for essential amino acids and vitamins was determined in wild-type Lactobacillus plantarum strains isolated from green olive fermentation brines. All the strains were found to be auxotrophic with respect to the amino acids but some of them were prototrophic for pyridoxal, p-aminobenzoic acid and/or nicotinic acid. Their growth response to these nutrients was also studied and found to be quite heterogeneous. Nutritional requirement pattern as a criteria for selecting starter cultures is discussed.

Plantaricins S and T, Two New Bacteriocins Produced by Lactobacillus plantarum LPCO10 Isolated from a Green Olive Fermentation

Twenty-six strains of Lactobacillus plantarum isolated from green olive fermentations were tested for cross-antagonistic activities in an agar drop diffusion test. Cell-free supernatants from four of these strains were shown to inhibit the growth of at least one of the L. plantarum indicator strains. L. plantarum LPCO10 provided the broadest spectrum of activity and was selected for further studies. The inhibitory compound from this strain was active against some gram-positive bacteria, including clostridia and propionibacteria as well as natural competitors of L. plantarum in olive fermentation brines. In contrast, no activity against gram-negative bacteria was detected. Inhibition due to the effect of organic acids, hydrogen peroxide, or bacteriophages was excluded. Since the inhibitory activity of the active supernatant was lost after treatment with various proteolytic enzymes, this substance could be classified as a bacteriocin, designated plantaricin S. Plantaricin S was also sensitive to glycolytic and lipolytic enzymes, suggesting that it was a glycolipoprotein. It exhibited a bactericidal and nonbacteriolytic mode of action against indicator cells. This bacteriocin was heat stable (60 min at 100°C), active in a pH range of 3.0 to 7.0, and also stable in crude culture supernatants during storage. Ultrafiltration studies indicated that plantaricin S occurred as multimolecular aggregates and that the size of the smallest active form is between 3 and 10 kDa. In sodium dodecyl sulfate-polyacrylamide gels, plantaricin S migrated as a peptide of ca. 2.5 kDa. Maximum production of plantaricin S was obtained in a fermentor system in unregulated pH and log-phase cultures of L. plantarum LPCO10 in MRS broth plus 4% NaCl. In these culture conditions, a second bacteriocin (designated plantaricin T) was produced in late-stationary-phase cultures of L. plantarum LPCO10. On the basis of its biological activity, its sensitivity to various enzymes, and its molecular weight (lower than that of plantaricin S) as assessed in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, plantaricin T appeared different from plantaricin S. Curing experiments with L. plantarum LPCO10 resulted in the appearance of variants that no longer produced either of the two bacteriocins but that were still immune to both of them.

Plasmid profiles and curing of plasmids in Lactobacillus plantarum strains isolated from green olive fermentations

Plasmid profiles of 35 Lactobacillus plantarum strains isolated from different green olive fermentors were obtained. A large number of plasmids in the CCC form (from 5 to 16) were present in all the tested strains as confirmed by a second dimension electrophoresis of DNA. These plasmids, all of which remain cryptic, ranged from 2.0 to 68 kb in size. Novobiocin, sodium dodecyl sulphate and ethidium bromide were used as plasmid-curing agents but only novobiocin induced loss of extrachromosomal DNA at a high frequency in these strains.