Virulence studies based on plasmid profiles of the fish pathogen Vibrio salmonicida

Strains of Vibrio salmonicida isolated from Atlantic salmon (Salmo salar) and rainbow trout (Salmo gairdneri) suffering from cold-water vibriosis could be divided on the basis of plasmid profiles into four different categories. Of 32 strains, 19% harbored three plasmids of 24, 3.4, and 26 megadaltons (MDa), 69% harbored the 24- and 3.4-MDa plasmids but not the 2.6-MDA plasmid, and 9% harbored only the 24-MDA plasmid. The fourth category, which consisted of only one strain, harbored a plasmid of 10 MDa. In spite of different plasmid patterns, the strains of V. salmonicida were very similar with respect to biochemical reactions. The one-third of the V. salmonicida strains which were serotyped were of the same type. The 50% lethal doses, which were determined by intraperitoneal injection, ranged from 4 x 106 to 1 x 108 CFU per fish.     

Levels of toxic and essential elements in arctic fox in Svalbard

Concentrations of cadmium, mercury, lead, arsenic, selenium, copper, zinc, manganese and iron in liver, and cadmium in kidneys, were analysed in 95 carcasses of arctic fox (Alopex lagopus) caught in Svalbard during three winter seasons from 1984 through 1986. The hepatic concentration ranges of cadmium, mercury, lead and arsenic were 0.1–2.4, 0.01–2.2, < 0.5–2.9 and 0.01–1.3 g·g^–1 WW, respectively. The range of cadmium concentration in the kidneys was from 0.2 to 13 g·g^–1 WW. Cadmium and mercury concentrations were higher in adult animals than in juveniles. The average concentrations of cadmium and lead were similar to recently published levels in polar bear from Svalbard, but the mercury concentrations were lower. Significant geographical differences were observed between trapping areas. Foxes caught north of Isfjorden had lower levels of liver iron and higher levels of all other elements analysed than those caught south of Isfjorden. The recorded concentrations of heavy metals indicate a moderate degree of exposure, which most likely is of natural origin.Gunnar Norheim died January 9, 1991     

Triploid Atlantic salmon Salmo salar have a higher dietary phosphorus requirement for bone mineralization during early development

The effect of a dietary phosphorus regime in freshwater on vertebra bone mineralization was assessed in diploid and triploid Atlantic salmon, Salmo salar. Fish were fed either a low phosphorus (LP) diet containing 10.5 g kg⁻¹ total phosphorus or a normal phosphorus (NP) diet containing 17.4 g kg⁻¹ total phosphorus from ∼3 to ∼65 g (day 126) in body weight. Two further groups were fed the NP diet from ∼3 g in body weight, but were then switched to the LP diet after 38 (∼10 g in body weight) or 77 (∼30 g in body weight) days. Growth, vertebral ash content (% ash) and radiologically detectable vertebra pathologies were assessed. Triploids were initially smaller than diploids, and again on day 77, but there was no ploidy effect on days 38 or 126. Vertebral ash content increased with increasing body size and those fish fed the NP diet had higher vertebral ash content than those groups fed the LP diet during the intervening time period, but this diet effect became less apparent as fish grew, with all groups having relatively equal vertebral ash content at termination. In general, triploids had lower vertebral ash content than diploids on day 38 and this was most evident in the group fed the LP diet. On day 77, those triploids fed the LP diet during the intervening time period had lower vertebral ash content than diploids. At termination on day 126, the triploids had the same vertebral ash content as diploids, irrespective of diet. There was a ploidy × diet interaction on vertebral deformities, with triploids having higher prevalences of fish with ≥1 deformed vertebra in all dietary groups except continuous NP. In conclusion, between days 0 and 77 (3–30 g body size), triploids required more dietary phosphorus than diploids in order to maintain similar vertebral ash content. A possible link between phosphorus feeding history and phosphorus demand is also discussed.     

Characterization of Microbial Diversity in Hypersaline Environments by Melting Profiles and Reassociation Kinetics in Combination with Terminal Restriction Fragment Length Polymorphism (T-RFLP)

The diversity of prokaryotes inhabiting solar saltern ponds was determined by thermal melting and reassociation of community DNA. These measurements were compared with fingerprinting techniques such as terminal restriction fragment length polymorphisms (T-RFLP) analysis, denaturant gradient gel electrophoresis (DGGE), and cloning and sequencing approaches. Three ponds with salinities of 22, 32, and 37% (NaCl saturation) were studied. The combination of independent molecular techniques to estimate the total genetic diversity provided a realistic assessment to reveal the microbial diversity in these environments. The changes in the prokaryotic communities at different salinity (22, 32, and 37% salt) were significant and revealed that the total genetic diversity increased from 22% to 32% salinity. At 37% salinity the diversity was reduced again to nearly half that at 22% salinity. Our results revealed that the community genome had a DNA complexity that was 7 (in 22% salinity pond), 13 (in 32% salinity pond), and 4 (in 37% salinity pond) times the complexity of an Escherichia coli genome. The base composition profiles showed two abundant populations, which changed in relative amount between the three ponds. They indicated an uneven taxon distribution at 22% and 37% salinity and a more even distribution at 32% salinity. The results indicated a large predominating population at 37% salinity, which might correspond to the abundance of square archaea (SPhT) observed by transmission electron microscopy (TEM) and also indicated by the same T-RFLP fragment as the SPhT. The SPhT phylotype has also been reported to be the most frequently retrieved phylotype from this environment by culture independent techniques. In addition, two different operational taxonomic units (OTU) were detected at 37% salinity based on PCR with bacterial specific primers and T-RFLP. One of these predominant phylotypes is the extreme halophilic bacterium belonging to the bacteroidetes group, Salinibacter ruber.     

A simple structured model describing the growth of Streptomyces lividans

The growth of Streptomyces lividans in defined media was modeled using a simple structured growth model. Conventional unstructured models like Monod kinetics, substrate inhibition kinetics, and the logistic equation were also used in an attempt to fit the data, but the results were all unsatisfactory. The main reason for failure in applying simple unstructured models is that they cannot describe the long lag phases sometimes observed during growth of S. lividans. The simple structured growth model was derived along similar principles to cybernetic growth models. This model quite accurately describes the growth of S. lividans. It assumes that the rate of assimilation of a substrate depends on the concentration of a specific key enzyme. This key enzyme is only produced in the presence of the substrate, and it is broken down at a steady rate. An enzyme synthesis allocation variable, w, similar to the cybernetic variable, u, described in cybernetic growth models, is proposed to control enzyme synthesis. Until the key enzyme concentration approaches its maximum level, very little substrate is consumed. And consequently, the lag phase is sustained.     

Reduction of hexavalent chromium in a reconstituted system of cytochrome P-450 and cytochrome b5

The reduction of hexavalent chromium (Cr(VI] by the monooxygenase components was studied. Both a reconstituted system of cytochrome P-450 (P-450) and cytochrome b5 (b5) with NADPH was capable of reducing Na2CrO4 (30 microM) provided anaerobic atmosphere. The rates were 1.29 nmol Cr.min-1 nmol P-450(-1) and 0.73 nmol Cr.min-1 nmol b5(-1). Using NADH instead of NADPH gave very low reducing activities, confirming the enzymic nature of the P-450 dependent Cr(VI) reductase reaction. Oxygen, 22% (air) and 0.1% gave 89% and 69% inhibition of Cr(VI) reducing activity, respectively. Carbon monoxide (100%) caused an inhibition of about 37% and 44% for P-450 and b5, respectively. Externally added flavin mononucleotide (FMN) (3 microM) or Fe-ADP (10 microM) to the complete system stimulated the enzymatic reaction about 2-fold and 3-fold, respectively.     

Plasmid profiling of Vibrio salmonicida for epidemiological studies of cold-water vibriosis in Atlantic salmon (Salmo salar) and cod (Gadus morhua).

In 1988, a new plasmid profile was observed for Vibrio salmonicida isolated from cod (Gadus morhua) and Atlantic salmon (Salmo salar) in fish farms in northern Norway. This new plasmid profile, which consisted of plasmids of 61, 21, 3.4, and 2.8 megadaltons, is 1 of 11 plasmid profiles which have so far been observed for V. salmonicida. Plasmid profiling and plasmid DNA hybridization were used in epidemiological studies of cold-water vibriosis. Our results indicate that V. salmonicida was transmitted from Atlantic salmon to cod and vice versa. The 61-megadalton plasmid was found exclusively in V. salmonicida strains originating from northern Norway, which is the only area in which this plasmid has ever been observed. Plasmid DNA hybridization and restriction endonuclease analysis show that the plasmid DNA of V. salmonicida remained stable throughout a 7-year survey.     

Chromosome analysis of five Brazilian species of poison frogs (Anura: Dendrobatidae)

Dendrobatid frogs have undergone an extensive systematic reorganization based on recent molecular findings. The present work describes karyotypes of the Brazilian species Adelphobates castaneoticus, A. quinquevittatus, Ameerega picta, A. galactonotus and Dendrobates tinctorius which were compared to each other and with previously described related species. All karyotypes consisted of 2n = 18 chromosomes, except for A. picta which had 2n = 24. The karyotypes of the Adelphobates and D. tinctorius species were highly similar to each other and to the other 2n = 18 previously studied species, revealing conserved karyotypic characteristics in both genera. In recent phylogenetic studies, all Adelphobates species were grouped in a clade separated from the Dendrobates species. Thus, we hypothesized that their common karyotypic traits may have a distinct origin by chromosome rearrangements and mutations. In A. picta, with 2n = 24, chromosome features of pairs from 1 to 8 are shared with other previously karyotyped species within this genus. Hence, the A. picta data reinforced that the C-banding pattern and the NOR location are species-specific traits in the genus Ameerega. Moreover, the Ameerega monophyletism proposed by previous phylogenetic studies indicates that the karyotypic differences among species in this genus result from a long divergence time.