Purification and characterization of a bacteriocin produced by Leuconostoc mesenteroides E131

Leuconostoc mesenteroides E131, isolated from Greek traditional fermented sausage, prepared without the addition of starters, produces a bacteriocin which is active against the pathogen Listeria monocytogenes. The bacteriocin was purified by 50% ammonium sulphate precipitation, cation exchange, and reverse-phase chromatography. Bacteriocin is active at pH values between 4.0 and 9.0 and retains activity after incubation for 1h at 100°C. Proteolytic enzymes inactivated the bacteriocin after 1h of incubation, while renin resulted in full inactivation only after 24h. Lipase resulted in full inactivation after 4h. Applying molecular methods, it was determined that the bacteriocin produced, named as mesenterocin E131, was identical to mesenterocin Y105 and was expressed during the exponential growth phase.

Diversity of Shewanella population in fish Sparus aurata harvested in the Aegean Sea

AIMS

To study the diversity of Shewanella population in Sparus aurata fish harvested in the Aegean Sea, as well as to elucidate the influence of fish storage conditions on the selection in Shewanella strains.

METHODS AND RESULTS

A total of 108 strains of Shewanella spp. were isolated from Sparus aurata during storage under various conditions. Conventional phenotypic analysis along with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of whole cell proteins and 16S rRNA sequence analysis were used for the characterization of the strains. Numerical analysis of whole cell protein profiles showed that the isolates were separated into two distinct clusters A and B with 47% similarity. Cluster B was further subdivided into two subclusters B1 and B2 with 70% similarity. One strain could not be assigned to any of these groups. The different ability of isolates to utilize deoxycholate, D-saccharate, D-glucuronate, N-acetyl-glycosamine, D-maltose, gluconate and citrate, as well as the different type of metabolism on the Hugh and Leifson medium distinguished the different Shewanella biogroups, as these were defined by the SDS-PAGE analysis. Representative strains from the three biogroups were further investigated by 16S rRNA sequence analysis and showed more than 99.4% similarity.

CONCLUSIONS

Significant similarities between the isolates and the type strains of S. baltica, S. putrefaciens and S. oneidensis at both phenotypic and molecular level signalize that the new isolates are closely related with the above Shewanella species, but do not provide a clear evidence to which of these species they belong.

SIGNIFICANCE AND IMPACT OF THE STUDY

The lack of information about the diversity of Shewanella population in Sparus aurata fish originated from Mediterranean Sea could be confronted using conventional phenotypic techniques, SDS-PAGE analysis of whole cell proteins and 16S rRNA sequencing.

The role and application of enterococci in food and health

The genus Enterococcus is the most controversial group of lactic acid bacteria. Studies on the microbiota of many traditional cheeses in the Mediterranean countries have indicated that enterococci play an important role in the ripening of these cheeses, probably through proteolysis, lipolysis, and citrate breakdown, hence contributing to their typical taste and flavour. Enterococci are also present in other fermented foods, such as sausages and olives. However, their role in these products has not been fully elucidated. Furthermore, the production of bacteriocins by enterococci is well documented. Moreover, enterococci are nowadays used as probiotics. At the same time, however, enterococci have been associated with a number of human infections. Several virulence factors have been described and the number of vancomycin-resistant enterococci is increasing. The controversial nature of enterococci has prompted an enormous increase in scientific papers and reviews in recent years, where researchers have been divided into two groups, namely pro and contra enterococci. To the authors' impression, the negative traits have been focused on very extensively. The aim of the present review is to give a balanced overview of both beneficial and virulence features of this divisive group of microorganisms, because it is only acquaintance with both sides that may allow their safe exploitation as starter cultures or co-cultures.

Lactobacillus acidifarinae sp. nov. and Lactobacillus zymae sp. nov., from wheat sourdoughs

Three heterofermentative lactic acid bacteria, obtained from Greek and Belgian artisanal wheat sourdoughs, were preliminarily identified as Lactobacillus brevis-like after screening using whole-cell protein fingerprinting and 16S rRNA gene sequence analysis. The three sourdough isolates showed nearly identical sequences (>99·7 % sequence similarity), and highest similarities of 98·2 and 97·6 % were obtained to the species Lactobacillus spicheri and Lactobacillus brevis, respectively. Growth characteristics, biochemical features, amplified fragment length polymorphism fingerprinting, DNA–DNA hybridizations and DNA G+C contents demonstrated that the isolates represent two novel Lactobacillus species. The names Lactobacillus acidifarinae sp. nov. and Lactobacillus zymae sp. nov. are proposed and the type strains are LMG 22200T (=R-19065T=CCM 7240T) and LMG 22198T (=R-18615T=CCM 7241T), respectively.

Influence of nutrients on growth and bacteriocin production by Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442

The aim of this study was to investigate the effect of complex nutrients on microbial growth and bacteriocin production, in order to improve bacteriocin synthesis during the growth cycle of Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442. The fermentations were conducted at the optimum pH and temperature for bacteriocin production (pH 5.5+/-0.1 and temperature 25+/-0.1 degrees C). Because of their association with the final biomass, conditions favouring the increase of the produced biomass resulted in the increase of bacteriocin activity in the growth medium. Since the produced final biomass and the final concentration of the bacteriocins were associated with the amount of the carbon (glucose) and nitrogen source, better growth of the lactic acid bacterial strains favoured the increase of the specific bacteriocin production. Additionally, the bacteriocin production was influenced by carbon/nitrogen ratio.

In vitro and in vivo inhibition of Helicobacter pylori by Lactobacillus casei strain Shirota

We studied the potential inhibitory effect of Lactobacillus casei strain Shirota (from the fermented milk product Yakult [Yakult Ltd., Tokyo, Japan]) on Helicobacter pylori by using (i) in vitro inhibition assays with H. pylori SS1 (Sydney strain 1) and nine H. pylori clinical isolates and (ii) the in vivo H. pylori SS1 mouse model of infection over a period of 9 months. In vitro activity against H. pylori SS1 and all of the clinical isolates was observed in the presence of viable L. casei strain Shirota cells but not in the cell-free culture supernatant, although there was profound inhibition of urease activity. In vivo experiments were performed by oral administration of L. casei strain Shirota in the water supply over a period of 9 months to 6-week-old C57BL/6 mice previously infected with H. pylori SS1 (study group; n = 25). Appropriate control groups of H. pylori-infected but untreated animals (n = 25) and uninfected animals given L. casei strain Shirota (n = 25) also were included in the study. H. pylori colonization and development of gastritis were assessed at 1, 2, 3, 6, and 9 months postinfection. A significant reduction in the levels of H. pylori colonization was observed in the antrum and body mucosa in vivo in the lactobacillus-treated study group, as assessed by viable cultures, compared to the levels in the H. pylori-infected control group. This reduction was accompanied by a significant decline in the associated chronic and active gastric mucosal inflammation observed at each time point throughout the observation period. A trend toward a decrease in the anti-H. pylori immunoglobulin G response was measured in the serum of the animals treated with lactobacillus, although this decrease was not significant.

Cloning and sequencing of the gene encoding X-prolyl-dipeptidyl aminopeptidase (PepX) from Streptococcus thermophilus strain ACA-DC 4

AIMS

To clone and sequence the pepX gene from Streptococcus thermophilus.

METHODS AND RESULTS

Three pairs of primers were used in polymerase chain reactions using as template the total DNA from Strep. thermophilus ACA-DC 4 in order to amplify, clone and sequence the pepX gene. Sequence analysis revealed an open reading frame of 2268 nucleotides encoding a protein of 755 amino acids. The calculated molecular mass of 85 632 Da agreed well with the apparent molecular mass of 80 000 Da previously determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and gel filtration for the monomeric form of the purified enzyme.

CONCLUSIONS

The pepX gene from Strep. thermophilus ACA-DC 4 was cloned and sequenced. The PepX protein showed significant sequence similarity with PepX enzymes from other lactic acid bacteria and contained a motif which was almost identical with the active site motif of the serine-dependent PepX family.

SIGNIFICANCE AND IMPACT OF THE STUDY

There are economic and technological incentives for accelerating and controlling the process of cheese ripening. To achieve this, starters may be modified by introducing appropriate genes from other food-grade bacteria. New or additional peptidase activities may alter or improve the proteolytic properties of lactic acid bacteria.

Characterization of Pseudomonas spp. associated with spoilage of gilt-head sea bream stored under various conditions

The population dynamics of pseudomonads in gilt-head sea bream Mediterranean fish (Sparus aurata) stored under different conditions were studied. Phenotypic analysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins were performed to identify a total of 106 Pseudomonas strains isolated from S. aurata stored under different temperatures (at 0, 10, and 20 degrees C) and packaging conditions (air and a modified atmosphere of 40% CO(2)-30% N(2)-30% O(2)). Pseudomonas lundensis was the predominant species, followed by Pseudomonas fluorescens, while Pseudomonas fragi and Pseudomonas putida were detected less frequently. Fluorescent Pseudomonas strains dominated under air conditions, while proteolytic and less lipolytic strains dominated under modified-atmosphere packaging. Different storage conditions appear to govern the selection of pseudomonads in gilt-head sea bream fish.

Citrate metabolism by Enterococcus faecalis FAIR-E 229

Citrate metabolism by Enterococcus faecalis FAIR-E 229 was studied in various growth media containing citrate either in the presence of glucose or lactose or as the sole carbon source. In skim milk (130 mM lactose, 8 mM citrate), cometabolism of citrate and lactose was observed from the first stages of the growth phase. Lactose was stoichiometrically converted into lactate, while citrate was converted into acetate, formate, and ethanol. When de Man-Rogosa-Sharpe (MRS) broth containing lactose (28 mM) instead of glucose was used, E. faecalis FAIR-E 229 catabolized only the carbohydrate. Lactate was the major end product, and small amounts of ethanol were also detected. Increasing concentrations of citrate (10, 40, 70, and 100 mM) added to MRS broth enhanced both the maximum growth rate of E. faecalis FAIR-E 229 and glucose catabolism, although citrate itself was not catabolized. Glucose was converted stoichiometrically into lactate, while small amounts of ethanol were produced as well. Finally, when increasing initial concentrations of citrate (10, 40, 70, and 100 mM) were used as the sole carbon sources in MRS broth without glucose, the main end products were acetate and formate. Small amounts of lactate, ethanol, and acetoin were also detected. This work strongly supports the suggestion that enterococcal strains have the metabolic potential to metabolize citrate and therefore to actively contribute to the flavor development of fermented dairy products.

Heterogeneity of Lactobacillus plantarum isolates from feta cheese throughout ripening

Thirty-two Lactobacillus plantarum strains isolated from Feta cheese throughout ripening were studied for their phenotypic characteristics, protein profile of cell-free extracts, enzyme profiles, plasmid profiles, proteolytic and acidifying abilities and ability to grow at low pH and in the presence of bile. Results showed that some biotechnologically important characteristics, such as acidifying and proteolytic activities, can differ between strains. In addition, different plasmid profiles suggest the presence of different Lact. plantarum strains in Feta cheese throughout ripening. The results suggest the possibility of choosing strains with specific biotechnologically interesting properties.

Biochemical properties of Streptococcus macedonicus strains isolated from Greek Kasseri cheese

A total of 32 Streptococcus macedonicus strains, isolated from Greek Kasseri cheese, were screened for biochemical properties of technological importance in milk fermentation processing, such as acid production, proteolytic and lipolytic activity, citrate metabolism, exopolysaccharide production, antimicrobial activity and biogenic amines production. All strains were found to be moderate acidifiers in milk. Only four strains could hydrolyse milk casein, while 11 strains showed lipolytic activity against tributyrin. Using amino acid derivatives of 4-nitroaniline as substrates, the highest peptidase activities were determined against phenylalanine- and glycine-proline-4-nitroanilide. Using fatty acid derivatives of 4-nitrophenol, it was shown that all strains exhibited esterase activities up to caprylate, with highest values against butyrate and caproate. Only one showed activity up to palmitate; this was also the most active strain against tributyrin. Five of the 32 strains could metabolize citrate but none of them produced exopolysaccharides. Nine strains displayed antimicrobial activity towards Clostridium tyrobutyricum, while no antimicrobial activity was detected against Listeria innocua and Propionibacterium freudenreichii subsp. shermanii. Finally, none was able to decarboxylize ornithine, histidine or lysine, and only four strains produced tyramine from tyrosine.

Polyphasic identification of wild yeast strains isolated from Greek sourdoughs

A total of forty-five wild yeast strains were isolated from five traditional Greek wheat sourdoughs. Strains were identified using the classical identification technique along with the sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole cell proteins (SDS-PAGE), Fourier transform-infrared spectroscopy (FT-IR) and the randomly amplified polymorphic DNA-polymerase chain reaction analysis (RAPD-PCR). The latter methods confirmed the classical identification. According to the results obtained, fourteen strains were identified as Saccharomyces cerevisiae strains, twenty-five as Pichia membranaefaciens strains and six as Yarrowia lipolytica.

Cell-wall-bound proteinase of Lactobacillus delbrueckii subsp. lactis ACA-DC 178: characterization and specificity for beta-casein

Lactobacillus delbrueckii subsp. lactis ACA-DC 178, which was isolated from Greek Kasseri cheese, produces a cell-wall-bound proteinase. The proteinase was removed from the cell envelope by washing the cells with a Ca2+-free buffer. The crude proteinase extract shows its highest activity at pH 6.0 and 40 degrees C. It is inhibited by phenylmethylsulfonyl fluoride, showing that the enzyme is a serine-type proteinase. Considering the substrate specificity, the enzyme is similar to the lactococcal PI-type proteinases, since it hydrolyzes beta-casein mainly and alpha- and kappa-caseins to a much lesser extent. The cell-wall-bound proteinase from L. delbrueckii subsp. lactis ACA-DC 178 liberates four main peptides from beta-casein, which have been identified.

Usefulness of rapid GC analysis of cellular fatty acids for distinguishing Weissella viridescens, Weissella paramesenteroides, Weissella hellenica and some non-identifiable, arginine-negative Weissella strains of meat origin

In an attempt to differentiate between Weissella viridescens, W. paramesenteroides, W. hellenica and some atypical arginine-negative Weissella isolates from meats, their cellular fatty acid composition was determined by a rapid GC method. Results showed that W. viridescens synthesized eicosenoic (n-C20:1) acid, while the other two species did not. Meanwhile, unlike W. paramesenteroides, W. hellenica lacked cyclopropane fatty acids with 19 carbon atoms, i.e. dihydrosterculic or lactobacillic acid. Weissella viridescens contained zero to low amounts (< 1%) of C19 cycl. Original meat isolates identified as W. viridescens or W. hellenica shared similar fatty acid profiles with the respective type strains, whereas the "wild" atypical Weissella isolates resembled more with W. paramesenteroides, and all together with Leuconostoc mesenteroides subsp. mesenteroides. Interesting variations were noted in the total C19 cycl contents among unidentified Weissella, being generally consistent with their grouping based on the type of lactate they formed and the whole-cell protein profile similarity they shared.

Identification of streptococci from Greek Kasseri cheese and description of Streptococcus macedonicus sp. nov

Taxonomic studies were performed on some Streptococcus-like organisms isolated from naturally fermented Greek Kasseri cheese. By SDS-PAGE analysis of whole-cell proteins the group was found to be quite different from Streptococcus thermophilus. Comparative 16S and 23S rRNA sequence analyses showed that the isolates represent a new species within the genus Streptococcus, where they are most closely related to the Streptococcus bovis cluster. On the basis of these phylogenetic results and some phenotypic differences, a new species, Streptococcus macedonicus, is proposed. The type strain is ACA-DC 206.

Purification and characterisation of an intracellular X-prolyl-dipeptidyl aminopeptidase from Streptococcus thermophilus ACA-DC 4

An intracellular X-prolyl-dipeptidyl aminopeptidase from Streptococcus thermophilus ACA-DC 4, isolated from traditional Greek yoghurt, was purified by anion exchange and gel filtration chromatography. A single band of molecular weight of about 80,000 appeared in SDS-PAGE; by gel filtration it was shown that the native enzyme was dimeric. The peptidase showed optimum activity on glycyl-prolyl 4-nitroanilide at pH 7.0 and at 50 degrees C, with K(m) = 3.1 mM and Vmax = 3500 U mg-1; over 50 degrees C the enzyme activity declined rapidly. It was inactivated by PMSF; sulfhydryl group reagents and metal chelators had little effect on enzyme activity.

Purification and partial characterization of an intracellular aminopeptidase from Streptococcus salivarius subsp. thermophilus strain ACA-DC 114

An intracellular aminopeptidase from Streptococcus salivarius subsp. thermophilus strain ACA-DC 114, isolated from traditional Greek yoghurt, was purified by chromatography on DEAE-cellulose and Sephadex G-100. The enzyme had a molecular weight of 89,000. It was active over a pH range 4.5-9.5 and had optimum activity on L-lysyl-4-nitroanilide at pH 6.5 and 35 degrees C with Km = 1.80 mmol/l; above 55 degrees C the enzyme activity declined rapidly. The aminopeptidase was capable of degrading substrates by hydrolysis of the N-terminal amino acid; it had very low endopeptidase and no carboxypeptidase activity. The enzyme was strongly inactivated by EDTA. Serine and sulphydryl group reagents had no effect on enzyme activity.