Sigridur Lara Gudmundsdottir

Density functional theory based screening of ternary alkali-transition metal borohydrides: A computational material design project

We present a computational screening study of ternary metal borohydrides for reversible hydrogen storage based on density functional theory. We investigate the stability and decomposition of alloys containing 1 alkali metal atom, Li, Na, or K (M(1)); and 1 alkali, alkaline earth or 3d/4d transition metal atom (M(2)) plus two to five (BH(4))(-) groups, i.e., M(1)M(2)(BH(4))(2-5), using a number of model structures with trigonal, tetrahedral, octahedral, and free coordination of the metal borohydride complexes. Of the over 700 investigated structures, about 20 were predicted to form potentially stable alloys with promising decomposition energies. The M(1)(Al/Mn/Fe)(BH(4))(4), (Li/Na)Zn(BH(4))(3), and (Na/K)(Ni/Co)(BH(4))(3) alloys are found to be the most promising, followed by selected M(1)(Nb/Rh)(BH(4))(4) alloys.

Physical activity and fertility in women: the North-Trøndelag Health Study

BACKGROUND Changes in the state of energy balance owing to changes in physical activity may affect the reproductive system. We evaluated the association between physical activity (PA) and fertility and parity in healthy women. METHODS A population-based health survey (HUNT 1) was conducted during 1984-1986 in Nord-Trøndelag county, Norway, with follow-up from 1995 to 1997 (HUNT 2). The study included 3887 women, <45 years old in HUNT 2. PA was assessed by baseline questionnaire, and fertility and parity by questionnaire at follow-up. Data focused on overall occurrence of infertility in the population (without biological confirmation). RESULTS Increased frequency, duration and intensity of PA were associated with increased subfertility, and frequency of PA was associated with voluntary childlessness (P < 0.01). After adjusting for age, parity, smoking, and marital status, women who were active on most days were 3.2 times more likely to have fertility problems than inactive women. Exercising to exhaustion was associated with 2.3 times the odds of fertility problems versus low intensity. Women with highest intensity of PA at baseline had the lowest frequency of continuing nulliparity and highest frequency of having three or more children during follow-up (P < 0.05). Sensitivity analysis including body mass index as confounder did not alter the results. No associations were found between lower activity levels and fertility or parity. CONCLUSION Increased risk of infertility was only found for the small group of women reporting the highest levels of intensity and frequency of PA. Awareness of the possible risks of infertility should be highlighted among non-athletic women who exercise vigorously.

Study of the humoral response of Atlantic salmon (Salmo salar L.), naturally infected with Aeromonas salmonicida ssp. achromogenes

The humoral antibody response of healthy Atlantic salmon and of two groups of salmon, naturally infected with Aeromonas salmonicida ssp. achromogenes, was examined in some detail. One diseased group was chronically infected and the other recently infected. It was found that the humoral response of these two infected groups was quite different. The chronically infected fish showed poor specific response to the causative agent whereas the recently infected salmon produced strong specific antibody response. The chronically infected fish showed evidence of increased unspecific response including an elevated level of natural antibodies. The specific humoral response of the recently infected fish was primarily directed against two cell-associated antigens of the A. salmonicida ssp. achromogenes bacterium, the A-layer protein and the o-polysaccharide component of LPS. In the chronically infected fish the humoral response was primarily directed against the A-layer protein.

Natural antibodies of cod (Gadus morhua L.): specificity, activity and affinity.

Natural antibodies are present in the serum of vertebrates regardless of antigenic stimulation. Characteristic activity is commonly detected against haptenated proteins, single stranded DNA and thyroglobulin. Natural antibodies are believed to provide an instant protection against pathogens of a broad specificity and to participate in homeostasis. Cod is a poor antibody responder but shows a relatively high level of natural antibodies against haptenated proteins. In this project the specificity, activity and affinity of natural antibodies was studied in different groups of cod and the effects of age/size, environmental temperature, immunisation and infection examined. Antigen driven selection of natural antibodies was also studied in one group of cod. The results demonstrated a broad and yet characteristic specificity, primarily directed against haptenated proteins and possible food antigens. The antibody activity increased with increasing age and at higher temperature whereas immunostimulation by immunisation or infection resulted in variable response. The affinity index of natural antibodies of cod generally did not correlate with changes in the antibody activity but it was in the same range as the affinity index of acquired cod antibodies and that of some mammalian monoclonal acquired antibodies. Analysis of antigen driven antibody selection showed that the natural antibody repertoire of individual cod was heterogeneous with respect to its affinity for haptenated protein.

Bacterial DNA indicated as an important inducer of fish cathelicidins.

Cathelicidins are antimicrobial peptides indicated as important in the control of the natural microflora as well as in the fight against bacterial invasion in mammals. Little is known about cathelicidins in fish and here the Chinook salmon (Oncorhynchus tshawytscha) embryo cell line (CHSE-214) was used as a model system to study the expression of cathelicidins due to fish pathogenic bacteria. The cDNA of cathelicidin from CHSE-214 cells (csCath) was cloned and shown to be closely related to gene 2 of both rainbow trout and Atlantic salmon. The deducted amino acid sequence showed highest sequence identity to rtCath2 with 95% and 72% for the cathelin and the antibacterial part, respectively. Cathelicidin gene expression was studied and various Gram positive and Gram negative bacteria caused the upregulation of the gene (csCath). Bacterial DNA and protein were shown important for the induction of cathelicidin expression in these cells. LPS (Escherichia coli) also causes the upregulation of cathelicidins, but digestion of the LPS with DNase I before incubation of the cells, totally abolished the upregulation of cathelicidin and suggests DNA contamination in the LPS to be the trigger for this effect. These results could explain the limited responsiveness of fish cells towards pure LPS and confirm previous suggestions that fish cells are less sensitive to LPS than mammalian cells.

Isolation of putative probionts from cod rearing environment.

Survival problems are encountered at early stages of intensive fish rearing and antibiotics are widely used to remedy the situation. Probiotics may provide a potential alternative method to protect larvae from opportunistic and pathogenic bacteria and promote a balanced environment. This study was designed to search for new probiotics to target this critical period in cod rearing. Potential probionts were selected from the natural microbiota of cod aquacultural environment. The selection was based on several criteria: pathogen inhibition potential, growth characteristics, strain identification, metabolite production and adhesion to fish cell lines. Our study demonstrated that 14% of screened bacteria (n=188) had antagonistic properties towards fish pathogens. The majority of these isolates were Gram-positive (81%), belonging to Firmicutes (69.2%) and Actinobacteria (11.5%) phyla based on 16S rRNA gene sequencing. Only 6 (3.2%) of 188 isolates could inhibit all three pathogens tested: Vibrio anguillarum, Aeromonas salmonicida subsp. achromogenes and Vibrio salmonicida. Differences observed in activity intensity and spectrum among inhibitory isolates emphasise the need to develop probiotic mixtures for efficient prophylactic methods. Comparison of growth behaviour of inhibitory isolates and pathogens at cod rearing temperatures, metabolite production and adhesion capacity were considered for final probiont selection. Four promising isolates that could be used as a mixed supplement to rearing water were identified as putative probiotic bacteria. This study emphasises the importance and potential of lactic acid bacteria in aquaculture.

Effects of bacterial treatment at early stages of Atlantic cod (Gadus morhua L.) on larval survival and development

Aims:  To assess the effects of bacterial treatment at the earliest stages of cod rearing on the microbial load, larval development and performance, testing three bacterial strains (Carnobacterium divergens V41, Arthrobacter sp. and Enterococcus sp.) in vivo that were previously shown to have inhibitory potential towards fish pathogens in vitro.

Microbiota of Atlantic cod (Gadus morhua L.) rearing systems at pre- and posthatch stages and the effect of different treatments.

Aims:  To study the effect of ova disinfection, antibiotic and microbial treatments on the dominant cultivable cod rearing microbiota at pre‐ and posthatch stages, determining some virulence‐related phenotypic traits among bacterial isolates and their relation to larval survival.

Age-Related Decline in Bone Mass Measured by Dual-Energy X-Ray Absorptiometry and Quantitative Ultrasound in a Population-Based Sample of Both Sexes: Identification of Useful Ultrasound Thresholds for Osteoporosis Screening

Quantitative ultrasound (QUS) can be used as a screening tool for low bone mineral density (BMD), but clinical guidelines have not been set. The aim of this population-based, cross-sectional study was to compare age-related changes in bone mass measured by QUS (Lunar, Achilles Plus) and dual-energy X-ray absorptiometry (DXA) in a random sample of 1630 individuals (1041 females, 589 males) 30-85 yr of age. Individuals with DXA T-scores < or =-2.5 at the femoral neck or total hip were identified and receiver operating curves (ROCs) were used to calculate cutoff points for QUS. Sensitivity, specificity, and kappa statistics were calculated. Age-related bone loss was significantly larger with QUS than DXA at all sites in women. For men, the curves were similar for QUS and DXA in the hip. Similar correlations were found between QUS and DXA in different age groups of both sexes (0.36-0.60). For women aged 50-65 yr, a QUS T-score >-1.0 was found to be the most applicable for identifying normal BMD. In the 70-85 yr age group, a T-score <-2.5 for women and a T-score <-0.5 for men seemed reasonable cutoffs for identifying normal BMD (sensitivity: 86-93%; specificity: 28-44%; discordance: 33-73%). Calcaneal QUS cannot be used for the diagnosis of osteoporosis according to WHO criteria, but it can be of use to exclude osteoporosis in 30-40% of our cases.

Isolation of two C-reactive protein homologues from cod (Gadus morhua L.) serum.

Pentraxins are important molecules in innate defence and play a role in the acute phase response of both mammals and fish. Isolation of cod pentraxins by affinity chromatography using phosphorylcholine agarose revealed two pentraxin-like proteins, referred to as PI and PII proteins. These varied in their overall charge, pentameric and subunit molecular size, glycosylation and N-terminal amino acid sequences. The PI protein was homologous with the CRP-like pentraxin previously described in cod whereas the PII protein was a new CRP homologue, which was characterized by substantial individual heterogeneity with regard to subunit size and relative density. The results indicate considerable genetic variations in the cod pentraxins.