Characterization of two bacteriocins produced by Pediococcus acidilactici isolated from "Alheira", a fermented sausage traditionally produced in Portugal

Lactic acid bacteria were isolated from "Alheira" sausages that have been sampled from different regions in Portugal. The sausages were produced according to different recipes and with traditional starter cultures. Two isolates (HA-6111-2 and HA-5692-3) from different sausages were identified as strains of Pediococcus acidilactici. Each strain produces a bacteriocin, designated as bacHA-6111-2 and bacHA-5692-3. Both bacteriocins are produced at low levels after 18 h of growth in MRS broth (3200 AU/ml against Enterococcus faecium HKLHS and 1600 AU/ml against Listeria innocua N27). BacHA-6111-2 and bacHA-5692-3 are between 3.5 kDa and 6.5 kDa in size, as determined by tricine-SDS-PAGE. Complete inactivation or significant reduction in antimicrobial activity was observed after treatment of cell-free supernatants with proteinase K, pronase and trypsin. No change in activity was recorded when treated with catalase. Both bacteriocins are sensitive to treatment with Triton X-114 and Triton X-100, but resistant to Tween 20, Tween 80, SDS, Oxbile, NaCl, urea and EDTA. The bacteriocins remained stable after 2 h at pH 6.0. A decrease in antibacterial activity was recorded after 60 min at 100 degrees C. After 60 min at 80 degrees C, 60 degrees C and 25 degrees C the antibacterial activity against L. innocua N27 decreased by 25%. Addition of bacHA-6111-2 and bacHA-5692-3 (1600 AU/ml) to a mid-log (5-h-old) culture of L. innocua N27 inhibited growth for 7 h. Addition of the bacteriocins (3200 AU/ml) to a mid-log (5-h-old) culture of E. faecium HKLHS repressed cell growth. The bacteriocins did not adhere to the surface of the producer cells. Both strains contain a 1044 bp DNA fragment corresponding in size to that recorded for pediocin PA-1. Sequencing of the fragments from both bacteriocins revealed homology to large sections of pedA (188 bp), pedB (338 bp) and pedC (524 bp) of pediocin PA-1 and the bacteriocins are considered similar to pediocin PA-1.     

Cryoprotectants-Free Vitrification and Conventional Freezing of Human Spermatozoa: A Comparative Transcript Profiling

Introduction: Spermatozoa cryopreservation is an important technique to preserve fertility for males. This study aimed at exploring the stability of epigenetics information in human spermatozoa, manipulated by two different technologies, freezing and vitrification. Methods: Spermatozoa samples were distributed into three groups: 1. Fresh spermatozoa (control group), 2. Frozen spermatozoa, 3. Vitrified spermatozoa. Epigenetic differences of fresh and cryopreserved spermatozoa were evaluated using high-throughput RNA sequencing. Results: Differentially expressed genes (DEGs) in frozen (1103 genes) and vitrified (333 genes) spermatozoa were evaluated. The bioinformatical analysis identified 8 and 15 significant pathways in groups of frozen and vitrified spermatozoa, respectively. The majority of these pathways are most relevant to immune and infectious diseases. The DEGs of the fertilization process are not detected during vitrification. The freezing process induces more down-regulation of genes and is relevant to apoptosis changes and immune response. Conclusion: Cryopreservation of human spermatozoa is an epigenetically safe method for male fertility preservation. Cryoprotectant-free vitrification can induce more minor biological changes in human spermatozoa, in comparison with conventional freezing.     

Advanced stochastic approaches for Sobol’ sensitivity indices evaluation

Neural Computing and Applications - Sensitivity analysis is a modern promising technique for studying large systems such as ecological systems. The main idea of sensitivity analysis is to evaluate...     

Lipschitz inverse shadowing for non-singular flows

We prove that Lipschitz inverse shadowing for non-singular flows is equivalent to structural stability.     

Effect of inulin on growth and bacteriocin production by Lactobacillus plantarum in stationary and shaken cultures

The prebiotic effect of inulin added to MRS medium on growth and bacteriocin production by L. plantarum ST16 Pa was investigated in stationary cultures in anaerobic jars with medium containing 0.025% sodium thioglycolate or in flasks shaken at 100 rpm. In the presence of 1% inulin in anaerobic stationary cultures, this strain produced lactic acid at a level that was 36.5% higher than in the absence of the polysaccharide. In shaken cultures without inulin, cell count was 54% higher than in the stationary ones. Under stationary conditions in anaerobic jars, the addition of inulin increased the maximum specific growth rate from 0.37 to 0.49 h^?1 and reduced the generation time from 1.85 h to 1.40 h. Consequently, the exponential phase was shortened from 12 to 9 h when the cells were grown in stationary cultures with the oxygen scavenger. Despite this effect of inulin on growth rate, stationary cultures without inulin displayed higher antimicrobial activity against Listeria monocytogenes L104 (3200 AU/mL) than cultures with inulin (1600 AU/mL); therefore, inulin behaved as a compound able to accelerate growth rather than to stimulate bacteriocin production. The results presented in this study are very promising, as L. monocytogenes is a well‐known foodborne pathogenic microorganism. Moreover, L. plantarum ST16 Pa has proven to be a potential producer of a natural food preservative at an industrial level.     

Partial Characterization of Nine Bacteriocins Produced by Lactic Acid Bacteria Isolated from Cold-Smoked Salmon with Activity against Listeria monocytogenes

Nine LAB bacteriocin-producers, isolated from vacuum-packaged cold-smoked salmon (CSS), were phenotypically and genotypically identified as Lactobacillus curvatus, Lactobacillus delbrueckii, Lactobacillus fermentum, Enterococcus faecium, and Pediococcus acidilactici. Their bacteriocins were partially characterized. The antimicrobial spectrum was determined against Listeria monocytogenes, E. faecalis, E. faecium, and Staphylococcus aureus. The molecular size of bacteriocins ranged from 2.8 to 4.5 kDa. They were inactivated by treatment with proteolytic enzymes but not by lipolytic or glycolytic enzymes. Maximal activity against L. monocytogenes ranged between 800 and 10000 AU/mL at pH 6.5. Most of the bacteriocins maintained full activity in a pH range of 2.0 to 8.0 but were partially or completely inactivated at pH 10.0. After heating at 60°C and 100°C, only two bacteriocins from Lb. curvatus strains partially lost activity. All bacteriocins showed a narrow spectrum of activity and a high anti-listerial activity, which is characteristic of the class IIa bacteriocins. Isolated bacteriocin-producing LAB could be used successfully in the bio-preservation of CSS and development of new potential bio-preservatives for CSS active against L. monocytogenes.     

Analysis and synthesis of perturbed Duffing oscillators

Analysis and synthesis of perturbed Duffing oscillators have been presented. The oscillations in such systems are regarded as limit cycles in perturbed Hamiltonian systems under polynomial perturbations of sixth degree and are analysed by using the Melnikov function. It has been proved that there exists a polynomial perturbation depending on the zeros of the Melnikov function so that the system considered can have either two simple limit cycles, or one limit cycle of multiplicity 2, or one simple limit cycle. A synthesis of such oscillators based on the Melnikov's theory has been proposed. Copyright © 2006 John Wiley & Sons, Ltd.     

The use of potassium iodide solution as photochemical actinometer for vacuum ultraviolet region

The paper has investigated the process of measuring power illumination for vacuum ultraviolet radiation by means of the solution of potassium iodide as a photochemical actinometer. We have investigated the formation of triiodide–ion when radiated the solution of light with wavelength 185 nm. It has been shown that obtaining hydroxyl radicals OH^– at this wavelength is determined by the formation of I ₃ ^– . The quantum yield of the process constitutes 0.165. Measuring the concentration of the obtained I ₃ ^– we determined power illumination of a quartz lamp DRB-20 (wavelength 185 nm), which constitutes 49.2 × 10^–9 E/s.