| 1. |
- Bastviken, David, et al.
(författare)
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Degradation of dissolved organic matter in oxic and anoxic lake water
- 2004
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 49:1, s. 109–116-
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Tidskriftsartikel (refereegranskat)abstract
- Decades of conflicting results have fueled a debate about how O-2 affects organic matter (OM) degradation and carbon cycling. In a laboratory study, using both OM taken directly from a humic lake and chemically isolated fulvic acid, we monitored the mineralization of dissolved OM in freshwater under purely oxic and anoxic conditions, under oxic then anoxic conditions, and under anoxic then oxic conditions, for 426 d. Between 5% and 24% of the initial OM was mineralized, with most extensive mineralization occurring under purely oxic and anoxic-oxic conditions. A sequential change in the O-2 regime did not result in greater overall degradation, but initially anoxic conditions favored subsequent oxic mineralization. A substantially greater fraction of the OM was degraded than in previous shorter studies, with as much as 50% of the total OM degradation occurring after 147 d into the experiment. Three fractions of the degradable OM were identified: OM degraded only under oxic conditions (68-78%), OM degraded more rapidly under anoxic conditions than under oxic conditions (16-18%), and OM degraded at equal rates under both oxic and anoxic conditions (6-14%). The degradation patterns of natural dissolved OM from a humic lake and chemically isolated fulvic acid were very similar, which indicates a similar level of bioavailability. The difference between anoxic and oxic degradation was greater in our long-term studies than in previous short-term experiments, which indicates that the oxic and anoxic degradation potentials vary with increasing overall OM recalcitrance and that similar oxic and anoxic degradation rates can be expected in short-term experiments in which <30% of the long-term degradable OM is allowed to decompose.
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| 2. |
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| 3. |
- Isaac, Giorgis, et al.
(författare)
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Total Lipid Extraction of Homogenized and Intact Lean Fish Muscles Using Pressurized Fluid Extraction and Batch Extraction Technique
- 2005
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 53:14, s. 5506-5512
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Tidskriftsartikel (refereegranskat)abstract
- The reliability and efficiency of pressurized fluid extraction (PFE) technique for the extraction of total lipid content from cod and the effect of sample treatment on the extraction efficiency have been evaluated. The results were compared with two liquid-liquid extraction methods, traditional and modified methods according to Jensen. Optimum conditions were found to be with 2-propanol/n-hexane (65:35, v/v) as a first and n-hexane/diethyl ether (90:10, v/v) as a second solvent, 115 oC, and 10 min of static time. PFE extracts were cleaned up using the same procedure as in the methods according to Jensen. When total lipid yields obtained from homogenized cod muscle using PFE were compared yields obtained with original and modified Jensen methods, PFE gave significantly higher yields, ~10% higher (t test, P < 0.05). Infrared and NMR spectroscopy suggested that the additional material that inflates the gravimetric results is rather homogeneus and is primarily consists of phospholipid with headgroups of inositidic and/or glycosidic nature. The comparative study demonstrated that PFE is an alternative suitable technique to extract total lipid content from homogenized cod (lean fish) and herring (fat fish) muscle showing a precision comparable to that obtained with the traditional and modified Jensen methods. Despite the necessary cleanup step, PFE showed important advantages in the solvent consumption was cut by ~50% and automated extraction was possible.
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| 4. |
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| 5. |
- Löfstedt, Christer, et al.
(författare)
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Analysis of moth pheromone acetates by selected ion monitoring using electron impact and chemical ionization mass spectrometry
- 1984
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Ingår i: Biological Mass Spectrometry. - : Wiley. - 0306-042X .- 1096-9888. ; 11:3, s. 106-113
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Tidskriftsartikel (refereegranskat)abstract
- Mass spectrometric determination of moth pheromone components by means of selected ion monitoring with electron impact and chemical ionization has been evaluated. For the analysis of acetates, chemical ionization with ammonia as reactant gas proved advantageous with respect to sensitivity and selectivity. A quantitative assay for determination of pheromone samples from individual turnip moth females (Agrotis segetum, Noctuidae), using internal standards, deuterated at the acyl group, was developed. The assay showed correct linearity in the investigated region (20–2000 pg). Signal to noise ratios for 100 pg of acetates using chemical ionization (ammonia as reactant gas) were in the range 10–50 depending on the degree of unsaturation. Conservative limits of detection (background signal + three times the standard deviation) and quantification (background signal + 10 times the standard deviation) were approximately 70 and 240 pg, respectively. A significant decrease in gland titre of (Z)‐5‐decenyl acetate and (Z)‐7‐dodecenyl acetate after mating was established.
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| 6. |
- Malmcrona-Friberg, Karin, et al.
(författare)
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Chemical changes in cell envelope and poly-β-hydroxybutyrate during short term starvation of a marine bacterial isolate
- 1986
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Ingår i: Archives of Microbiology. - 0302-8933. ; 144:4, s. 340-345
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Tidskriftsartikel (refereegranskat)abstract
- Qualitative and quantitative changes were observed in lipids, poly-β-hydroxybutyrate (PHB), and a cell wall peptidoglycan consitutent in a marine bacterial isolate during starvation for 24 h in an energy and nutrient-free medium. While the amount and composition of the membrane fatty acids fluctuated within the first hours of starvation, the total amount of fatty acids decreased during the starvation period. Furthermore, the ratio of monounsaturated to saturated fatty acids decreased and the proportion of short chain fatty acids increased. In the very early phase of starvation the bacteria contained PHB, which had been accumulated during the growth phase, but after 3 h no PHB was detected. Cells starved for phosphorus showed a different pattern as PHB was initially accumulated and did not decrease until 5 h of starvation. Synthesis of the cell wall amino acid d-alanine was initiated during the first phase of starvation. The effects of these changes on membrane fluidity and uptake of substrates as well as the use of fatty acids and PHB as energy resources during starvation are discussed.
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| 7. |
- Mårdén, Per, et al.
(författare)
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Physiological and morphological changes during short term starvation of marine bacterial islates
- 1985
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Ingår i: Archives of Microbiology. - 0302-8933. ; 142:4, s. 326-332
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Tidskriftsartikel (refereegranskat)abstract
- Three marine bacteria were examined for physiological and morphological changes in the initial phase of starvation. It was found that the starvation process was induced in a similar way irrespective of whether the cells were suspended in nutrient and energy free artificial seawater (NSS) or NSS supplemented with nitrogen and phosphorus. An initial phase of increased activity was consistent with a decreased response to added nutrients. Recovery from starvation exhibited the same response in both these starvation regimes, measured throughout the starvation period. Cells in nitrogen or phosphorus deprived starvation regimes, showed a high and rapid increased activity, followed by a delayed and more pronounced decline in respiratory activity. The initial phase of starvation also included a loss of poly-β-hydroybutyrate as observed by transmission electron microscopy (TEM). Two bacterial strains showed formation of small vesicles on the outer cell layer when examined by TEM. This formation and release of vesicles was related to the continuous size reduction during starvation survival. The results are discussed in terms of defining the mechanisms of initial cellular responses to nutrient deprivation.
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| 8. |
- Persson, Linn, et al.
(författare)
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Electrospray mass spectrometry to study lake water DOM and effects of microbial degradation
- 2005
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Ingår i: International Journal of Environmental Analytical Chemistry. - : Taylor & Francis Group. - 0306-7319 .- 1029-0397. ; 85:1, s. 15-27
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Tidskriftsartikel (refereegranskat)abstract
- Qualitative analysis of lake water dissolved organic matter (DOM) was carried out using electrospray ionization mass spectrometry (ESI MS) without prior clean-up or chromatography, showing the potential of ESI MS as a rapid method to analyse qualitative differences between DOM with different environmental properties. Spectra were evaluated in terms of the relative ion abundance in certain mass to charge ranges (m/z(range)), and the mass-to-charge average (m/z(average)). Lake water DOM from two different sources was used. In addition, DOM from both sources that had been subjected to microbial degradation under different oxygen regimes was analysed. ESI MS results were compared with those of UV absorbance and pollutant binding capacity (pyrene and atrazine). The results from all methods indicated qualitative differences between the DOM from different lakes, but only minor qualitative changes when comparing oxic and anoxic degradation. To detect those small differences the m/z(range) proved to be the more sensitive evaluation method, compared to the m/z(average).
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| 9. |
- Tunlid, Anders, et al.
(författare)
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Capillary gas chromatography using electron capture or selected ion monitoring detection for the determination of muramic acid, diaminopimelic acid and the ratio of d/l-alanine in bacteria
- 1983
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Ingår i: Journal of Microbiological Methods. - : Elsevier BV. - 0167-7012. ; 1:2, s. 63-76
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Tidskriftsartikel (refereegranskat)abstract
- Gas chromatographic analyses of muramic acid, diaminopimelic acid and D-alaline, which are specific components of the bacterial cell wall, have been performed using electron capture or selected ion monitoring detection. Intact cells or peptidogylycan preparations were hydrolyzed in HCl and DCl. After purification by cation exchange chromatography, followed by conversion to the N-heptafluobutyrliso-butyl esters, the components were separated on a 25 m fused silica column coated with SE-54 or on a chiral glass capillary column. The detection limits for muramic acid and diaminopimelic acid were about 10 pg using either detection method and the procedure has the potential sensitivity for detecting about 3 × 105 bacterial cells, e.g., Escherichia coli. Mass spectrometric determination of the d/l ratio of alamine in intact cells of Group A streptococci, type M 15 and in peptidogylcan preparations thereof indicated the proportions 10.2% and 10.5% of D-alanine, respectively. The values uncorrected for racemization during acid hydrolysis were 10.3% and 10.7%, respectively.
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| 10. |
- Tunlid, Anders, et al.
(författare)
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Determination of 13C-enrichment in bacterial fatty acids using chemical ionization mass spectrometry with negative ion detection
- 1987
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Ingår i: Journal of Microbiological Methods. - : Elsevier BV. - 0167-7012. ; 7:2-3, s. 77-89
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Tidskriftsartikel (refereegranskat)abstract
- Saturated, monoenoic and β-hydroxysubstituted fatty acids, 13C-labelled at the carboxyl group, were prepared from natural or synthetic unlabelled analogues. The synthetic route involves decarboxylation of the unlabelled fatty acid to the next lower iodide, displacement of iodide for [13C]cyanide and hydrolysis. The fatty acids were converted to their pentafluorobenzyl esters and analysed by selected ion monitorint using chemical ionization and negative ion detection. Measurements of the signal ratios for the negative carboxylate ion (m) and the (m + 1) ion showed that at 95% confidence level and n = 5, mean values differing by 1.0 atom% 13C will be significantly resolved. The calculated standard deviation was the same for the studied bacterial acids including the phospholipid ester-linked palmitoleic acid, β-hydroxymyristic acid in the lipopolysaccharides and β-hydroxybutyric acid in the storage polymer poly-β-hydroxyalkanoate. Sodium [1-13C]acetate or D-[13C6]glucose were pulse administered to a Gram-negative marine bacterium isolate. Phospholipid ester-linked fatty acids and β-hydroxybutyric acid showed extensive 13C-incorporation within 15 min after the pulse. After approximately 60 min a maximum of 10 atom% excess of 13C was reached for palmitoleic acid. The method provides the potential to measure the metabolic activity of bacterial communities by measuring the incorporation of 13C-labelled substrates into specific fatty acids that can be utilized as biomarkers for biomass, community structure and nutritional status.
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