Moritella viscosa causes winter ulcer disease in salmonids. The aim of the present work was to isolate and partially characterise an extracellular peptidase from M. viscosa, and to study its role in virulence. The peptidase, termed MvP1, was a 38-kDa metallopeptidase produced in late exponential growth. The optimum temperature for MvP1 was 40 °C, but the enzyme was active over a broad range of temperatures. MvP1 was non-lethal to salmon at concentrations up to 0.22 μg/g fish, but extracellular products were lethal to salmon. MvP1 degraded casein, gelatin and collagen from lumpfish skin. It caused considerable tissue necrosis and hemorrhages at the site of injection, and affected cell–cell adhesions in EPC and BF-2 cell lines, but was not highly cytotoxic. The peptidase partially degraded fish IgM heavy chain but was non-hemolytic. The mvp1 gene was sequenced and encoded a 734-aa polypeptide containing a signal sequence, an N-terminal propeptide, a mature peptidase domain and a C-terminal propeptide. The MvP1 propeptide undergoes both N-terminal and C-terminal processing and different C-terminal processing results in the formation of several active isoforms of the mature peptidase. The catalytic domain showed highest sequence similarity with several vibriolysins (EC 3.4.24.25) originating from Pseudoalteromonas strains, showing up to 80% aa identity. The results indicate that MvP1 is a previously unknown vibriolysin that might affect M. viscosa virulence by aiding in the invasion and dissemination of the bacterium in its host, by causing tissue destruction.
Flokkur: Greinar
Strains PRI 2268 and PRI 3838T were isolated from two separate hot springs in the Torfajokull geothermal area of South Iceland. The cells were non-motile rods, approximately 0.3 μm in width and 1.5–2.5 μm in length. Electron microscopy revealed a Gram-negative cell-wall structure. The strains grew at 45–79 °C (optimum, 65 °C) and pH 5.5–10.5 (optimum, pH 6.0–7.0). 16S rRNA gene sequence analysis indicated that they formed a separate branch within the genus Thermus with ‘Thermus kawarayensis’ KW11 as their closest cultured relative (96.5 % similarity). The gene sequence similarities of both new isolates to Thermus aquaticus YT-1T and Thermus igniterrae RF-4T were 96.1 % and 95.5 %, respectively. DNA–DNA relatedness between strain PRI 3838T and ‘T. kawarayensis’ was 46.1 %. The DNA G+C content of strain PRI 3838T was 69.0 mol%. The predominant menaquinones, pigmentation, fatty acid profiles and phospholipid profiles of the novel strains were similar to those of other members of the genus Thermus. However, the new strains could be differentiated from the type strains of all other species of the genus Thermus by their lack of catalase activity and their utilization of only a few carbon sources. Furthermore, the novel strains exhibited mixotrophic growth with sulfur oxidation. On the basis of 16S rRNA gene sequence comparisons, DNA–DNA hybridization and physiological and biochemical characteristics, the new isolates represent a novel species. Since the species appears to be ubiquitous in Icelandic hot springs, the name Thermus islandicus sp. nov. is proposed. The type strain is PRI 3838T (=DSM 21543T=ATCC BAA-1677T).
The availability of information on the population’s exposure to the biological agents is crucial for characterising the risks of associated food-borne pathogens. Unfortunately, the available exposure data are insufficient to assess the public health impact of pathogens. Effective dose-response models are required to evaluate the risks. The growth of the micro-organisms in the food is also important. The prediction of the microbial population in food plays important role in finding the risk of certain adverse effects on human population. This study combines the stochastic growth models with the dose-response models to find the risk of illness in consumers due to the consumption of contaminated food. Keywords: stochastic model, listeria, probability of illness.
Health claim perception was investigated by a web-based instrument with a sample of 4,612 respondents in the Nordic countries (Denmark, Finland, Iceland, Norway, Sweden). Respondents decided which of a pair of claims sounded better, was easier to understand and was more convincing in their opinion. Claims were constructed from an underlying universe combining different active ingredients (familiar, unfamiliar), type of claim (combination of information about ingredient, physiological function and health benefit), framing (positive, negative), and use of qualifier (with, without “may”). Across pairs, the claims differed in the health benefit addressed (cardiovascular health, dementia, bodyweight). Results showed that respondents could be grouped into two roughly equally sized classes that differed in the type of claim preferred: one class prefers “long” claims that give the full story consisting of active ingredient, physiological function and health benefit, whereas the other prefers “short” claims consisting of the health benefit only. Results also showed that the familiar ingredient is preferred to the unfamiliar one, whereas effects of positive versus negative framing depended on the type of health benefit addressed.
BACKGROUND: Minolta and machine vision are two different instrumental techniques used for measuring the colour of muscle food products. Between these two techniques, machine vision has many advantages, such as its ability to determine L*, a*, b* values for each pixel of a sample’s image and to analyse the entire surface of a food regardless of surface uniformity and colour variation. The objective of this study was to measure the colour of irradiated Atlantic salmon fillets using a hand-held Minolta colorimeter and a machine vision system and to compare their performance.
RESULTS: The L*, a*, b* values of Atlantic salmon fillets subjected to different electron beam doses (0, 1, 1.5, 2 and 3 kGy) were measured using a Minolta CR-200 Chroma Meter and a machine vision system. For both Minolta and machine vision the L* value increased and the a* and b* values decreased with increasing irradiation dose. However, the machine vision system showed significantly higher readings for L*, a*, b* values than the Minolta colorimeter. Because of this difference, colours that were actually measured by the two instruments were illustrated for visual comparison. Minolta readings resulted in a purplish colour based on average L*, a*, b* values, while machine vision readings resulted in an orange colour, which was expected for Atlantic salmon fillets.
CONCLUSION: The Minolta colorimeter and the machine vision system were very close in reading the standard red plate with known L*, a*, b* values. Hence some caution is recommended in reporting colour values measured by Minolta, even when the ‘reference’ tiles are measured correctly. The reason for this discrepancy in colour readings for salmon is not known and needs further investigation. Copyright © 2009 Society of Chemical Industry
The effect of high pressure treatment (HPP) (150 MPa and 300 MPa for 15 min) and cooking on quality of Atlantic salmon based on microbial activity, lipid oxidation, fatty acid profile, colour and texture during 6 days of storage was studied. High pressure and cooking significantly (p < 0.05) reduced microbial growth. The 300 MPa treatment and cooking showed higher L∗ and b∗ values but lower a∗ values for dark muscle compared to control and samples treated at 150 MPa. An increase in pressure resulted in an increase in hardness, gumminess and chewiness parameters, and a decrease in adhesiveness compared to control and cooked samples. Whereas cooking and 150 MPa led to similar oxidation development as control in dark muscle, the 300 MPa treatment effectively reduced the samples susceptibility to oxidation. Fatty acid profile of cooked Atlantic salmon dark muscle showed significantly (p < 0.05) lower amounts of total saturated, n−3 Polyunsaturated fatty acids (PUFA) and n−6 PUFA and significantly (p < 0.05) higher amounts of monoenes than HPP treated samples during the entire storage period. However, the most important finding of this study was that there was no significant (p > 0.05) difference between control and HPP treated samples in terms of total saturated, monoenes, n−3 PUFA and n−6 PUFA fatty acid profile. This demonstrates that HPP is a very mild process in terms of its effect on fatty acids.
Fish protein isolates (FPI) from cod muscle were studied at pH 9 and 11. Thermo-reversible gels, stable at and below room temperature could be produced at both pH values. Application of low shear stress to the gels led to an initial elastic response followed by a power-law deformation (creep) at both pH. Above a critical shear stress gels fractured and flowed regularly with a viscosity of about 0.05 Pa s.
Strain–stress curves were recorded using both flow and oscillatory measurements. For all systems strain-hardening was observed followed by fracture. Fracture occurred at approximately the same deformation, but the amplitude of strain-hardening and the yield stress decreased with decreasing rate of the stress ramp. Results obtained from oscillatory shear at 1 or 0.1 Hz were close to those obtained with continuous shear during the fastest stress ramps.
The structure of the gels was investigated using confocal laser scanning microscopy and turbidity measurements.
Cultivation and culture-independent techniques were used to describe the geothermal ecosystem of the Blue Lagoon in Iceland. The lagoon contains both seawater and freshwater of geothermal origin and is extremely high in silica content. Water samples were collected repeatedly in summer and autumn in 2003 and 2005 and in winter 2006 were analyzed for species composition. The study revealed the typical traits of an extreme ecosystem characterized by dominating species and other species represented in low numbers. A total of 35 taxa were identified. The calculated biodiversity index of the samples was 2.1–2.5. The majority (83%) of analyzed taxa were closely related to bacteria of marine and geothermal origin reflecting a marine character of the ecosystem and the origin of the Blue Lagoon hydrothermal fluid. A high ratio (63%) of analyzed taxa represented putative novel bacterial species. The majority (71%) of analyzed clones were Alphaproteobacteria, of which 80% belonged to the Roseobacter lineage within the family of Rhodobacteraceae. Of seven cultivated species, the two most abundant ones belonged to this lineage. Silicibacter lacuscaerulensis was confirmed as a dominating species in the Blue Lagoon. One group of isolates represented a recently identified species within the genus of Nitratireductor within Rhizobiales. This study implies an annually stable and seasonally dynamic ecosystem in the Blue Lagoon.
A pollock protein hydrolysate was used for enrichment of the live feed offered to halibut larvae from the onset of exogenous feeding and the effects of treatment on selected innate immune parameters studied. The effects of treatment on the bacterial community structure of larvae were furthermore studied using the PCR–DGGE method. C3 and lysozyme were identified in larvae already at the onset of first feeding and low concentrations of IgM detected at this stage indicate maternal origin. Endogenous production of IgM was validated in the gastrointestinal tract of larvae from 29 days post onset of first feeding, with similar concentrations found in both groups. Feeding the peptide-enriched live feed stimulated production of lysozyme and affected the distribution of C3 in larval tissue but survival and normal development of halibut larvae were not affected by the treatment. Vibrio sp. and Pseudoalteromonas sp. dominated the bacterial community of larvae from both groups and peptide enrichment of the live feed was not found to affect the bacterial community structure associated with surface sterilized larvae.
Peeled, headed or whole shrimp (Pandalus borealis) was dried in a heat-pump dryer at -2-0℃ and 20℃, respectively, and desorption isotherms characterizing the dehydration property of each shrimp sample group were determined. Desorption isotherms of shrimp handled differently and dried at different temperatures (-2-0℃ or 20℃) could be well described by Oswin’s model (() 1 w n w a Xa a = −). The regression model of peeled, headed or whole shrimp was established, which is reliable for predicting the desorption isotherms of shrimp undergoing heat-pump drying. The handling methods of shrimp exhibit measurable influence on desorption isotherms of shrimp, whereas drying temperature (-2-0℃ or 20℃) has little influence on the constants of a and n in Oswin’s model, of whole shrimp, even though it has certain influence on these constants of peeled and headed shrimp. For heat-pump drying, headed shrimp may have a better stability than peeled or whole shrimp due to the best stability.