Annette Pettersson

Accumulation of Aluminium by Anabaena cylindrica into Polyphosphate Granules and Cell Walls: an X-ray Energy-dispersive Microanalysis Study

Summary: X-ray microanalysis of thin cryosections of the cyanobacterium Anabaena cylindrica showed that aluminium was rapidly taken up and accumulated into polyphosphate granules. In addition, aluminium was found in the cell walls but could not be detected in the cytoplasm. The concentration of phosphorus in the medium affected the accumulation pattern; more aluminium was bound in the polyphosphate granules and in the cell walls after growth in phosphorus-rich medium. The accumulation of aluminium in these structures may function as a detoxification mechanism. Treatment with aluminium for 24 h did not cause any significant changes in the elemental composition of polyphosphate granules or cell walls.

Competition between the green alga Scenedesmus and the cyanobacterium Synechococcus under different modes of inorganic nitrogen supply

In this study, we evaluated growth responses of the green alga Scenedesmus and the cyanobacterium Synechococcus supplied with inorganic nitrogen in different ways. A competitive situation in which nitrogen was limiting was created in mixed cultures as well as in cultures growing in the same vessel but separated by a permeable dialysis membrane. Supplying inorganic nitrogen in small pulses at a high frequency favoured the cyanobacterium Synechococcus, whereas batch additions favoured the green alga Scenedesmus. When using a large-pulse/low-frequency supply mode, the yield of the green alga was higher when ammonium was added as nitrogen source compared to when nitrate was added. By contrast, the yield of the cyanobacterium was higher in the nitrate regime. However, uptake experiments using unialgal cultures showed that both organisms depleted the medium of ammonium more rapidly than they depleted the medium of nitrate; i.e. the higher yield of the cyanobacterium in the nitrate regime than in the ammonium regime can be attributed to the effects of competition with the green alga. Since nitrate assimilation involves the consumption of reductive power, we suggest that the outcome of competition was governed by the fact that green alga was light limited and therefore better able to compete for ammonium than for nitrate. The results from the laboratory studies are discussed in relation to results from an enclosure experiment performed in Lake Erken, Sweden. In that field experiment, in which additions of both phosphate and ammonium were applied every second day to 350-l enclosures, the green algal biomass increased exponentially during an incubation period of 22 days.

Comparison of fatty acid composition and astaxanthin content in healthy and by M74 affected salmon eggs from three Swedish river stocks

M74 is an extremely lethal syndrome appearing during the yolk sac-swim up stage. The syndrome is known in the Baltic Sea salmon but is still unknown in Atlantic salmon. In this study, Baltic salmon eggs from females showing M74 syndrome were compared with those from healthy females. Further, the study also included a comparison between eggs from a western (Atlantic) and two eastern (Baltic) Swedish stocks. We found differences between the Atlantic and Baltic stocks in the content of 22:6 (n-3) both in the phospholipid and triacylglycerol lipid fractions (P<0.013, P<0.0001, respectively). In addition, the eggs from the Baltic stocks had a much lower astaxanthin content than the west coast stock (P<0.0001). In the phospholipid fraction, an inverse relation was found between river temperature and 22:6 (n-3) content, when rivers were arranged according to day degrees during egg development. M74 affected eggs had a higher content of 22:6 (n-3) compared to non-affected M74 ones. We found differences in the (n-3)/(n-6) ratio between healthy and M74 eggs (P<0.0046). Also, the astaxanthin content was significantly lower in M74 eggs (P<0.0018). We suggest that egg lipid composition is under strong genetic influence. Further, we suggest that in healthy eggs of Baltic salmon, there is a balance between oxidative potential and antioxidant capacity and that a disturbance of this balance at the cellular level could possibly be a cause of the M74 syndrome.

Aluminium Uptake by Anabaena cylindrica

Summary: Atomic absorption spectrophotometry was used to characterize aluminium uptake by the cyanobacterium Anabaena cylindrica. An EDTA-washing procedure was used to distinguish between adsorbed and intracellular aluminium. The intracellular aluminium content increased with increasing external concentration and time. The phosphorus concentration in the growth medium did not affect the rate of aluminium uptake nor did dark treatment or addition of CCCP, an uncoupler of phosphorylation. We therefore conclude that aluminium toxicity is due to intracellular aluminium rather than to interactions with nutrients in the growth medium and that aluminium uptake is independent of phosphorus uptake. The accumulation of aluminium in polyphosphate granules and cell walls of phosphorus-rich cells noted earlier is rather due to an increased binding capacity in these cellular compartments. Also, the rapid uptake of aluminium by A. cylindrica mainly occurs via passive diffusion.

Eggs of Baltic salmon displaying M74, yolk sac mortality syndrome have elevated levels of cholesterol oxides and the fatty acid 22:6 n-3

Abstract In this study, level of cholesterol oxidation products (COPs), fatty acids and carotenoids were compared between healthy and M74 yolk sac mortality syndrome-affected eggs in two Swedish stocks of Baltic salmon ( Salmo salar ). In addition were eggs from one stock of Atlantic salmon, originating from a Swedish west coast river analysed. This syndrome is believed to be the result of a combined environmental load of anthropogenic substances like chloroorganic pollutants and their metabolites. The syndrome is so far only found in Baltic salmon spending their post-smolt period in the Baltic Sea. COPs were significantly higher ( p =0.0289) in Baltic salmon eggs suffering from M74 than in healthy eggs, while no difference was found between healthy Baltic salmon eggs and those from the Atlantic stock ( p >0.05). The absolute level of COPs varied between rivers and year classes, while the level of cholesterol was relatively stable. However, the level of COPs was always higher in the M74-affected eggs compared to their healthy counterparts. The content of the fatty acid 22:6 n-3 (DHA; docosahexaenoic acid) was higher and astaxanthin lower in M74-affected eggs ( p =0.0056; p =0.0078, respectively) compared to healthy ones of the same stock and year class.

Bioassay for phosphate demand in phytoplankton from acidified lakes: Lake Njupfatet, an example of phosphate deficiency induced by liming

A bioassay was developed, involving steady-state ATP level determinations, for estimation of phosphate demand and deficiency in natural phytoplankton communities. The studies were performed on phytoplankton from the moderately acidified Lake Njupfatet in central Sweden before and after liming. Phytoplankton samples from in situ enclosure experiments with low-dose enrichments of nitrate and phosphate and removal of large (> 100 µm) zooplankton and from the lake water were collected. The phytoplankton were concentrated by through-flow centrifugation and post-cultured in the laboratory with or without the addition of phosphate. A relative increase in the ATP:chlorophyll a ratio after the phosphate treatment as compared to samples without phosphate enrichment was found to be a highly reproducible indicator of phosphate deficiency in the natural phytoplankton population. In contrast, the absolute ATP:chlorophyll a ratio varied substantially between different sampling occasions. No phosphate deficiency was detected in phytoplankton from the acidic lake or from fertilized in situ enclosures. However, phytoplankton from in situ enclosures without added nutrients showed evidence of phosphate limitation after 21 days incubation. Also, the phytoplankton community developed a significant phosphate deficiency the summer after lake liming. The results from the ATP analyses are compared with chemical data of the lake water, phytoplankton community structure and phosphatase activities in the lake before and after liming. The average total biomass of phytoplankton and the average Tot-P measured during May to September decreased with appr. 30% after liming while Tot-N was essentially unaffected and the phosphatase activities increased by 1000–2000%.