| 1. |
- Barreiro, A, et al.
(författare)
-
Relative importance of the different negative effects of the toxic haptophyte Prymnesium parvum on Rhodomonas salina and Brachionus plicatilis
- 2005
-
Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 38:3, s. 259-267
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to determine the relative importance of the different processes/mechanisms by which the toxic haptophyte Prymnesium parvum, cultured under different nutrient conditions, affects non-toxic phytoplankton competitors and microzooplankton grazers. P. parvum was cultured under steady-state growth in different nutrient conditions: nitrogen depleted (-N), phosphorus depleted (-P) and balanced nitrogen and phosphorus (+NP). Cells from each nutrient condition and culture cell-free filtrates, alone and combined with non-toxic prey (Rhodomonas salina), were used as food for the rotifer Brachionus plicatilis. An additional experiment was carried out to test the effect of P. parvum cells and culture cell-free filtrate on R. salina. The highest haemolytic activity values were achieved by -P F parvum cultures, followed by -N. However, the negative effect of R parvum on R. salina and rotifers did not correlate with haemolytic activity but with the number of P. parvum cells. -N-cultured P. parvum were the most toxic for both R. salina and rotifers, followed by +NP. Therefore, haemolytic activity is not a good indicator of the total potential toxicity of R parvum. The growth rate of R. salina was negatively affected by cell-free filtrates but the effect of P, parvum predation was greater. Rotifers fed on both toxic and non-toxic algae, indicating that they did not select against the toxic alga. The P. parvum cell-free filtrate had an effect on B. plicatilis, although this was weak, B, plicatilis was also indirectly affected by P. parvum due to the negative effects of the toxic alga on their prey (R. salina). However, the greatest negative effect of P. parvum on the rotifers was due to ingestion of the toxic cells. Therefore, the phytoplankton competitor R. salina is more affected by P. parvum predation and the grazer B. plicatilis is more affected by ingestion of the toxic cells, the effects of excreted compounds being secondary.
|
|
| 2. |
|
|
| 3. |
- Sopanen, S, et al.
(författare)
-
Prymnesium parvum exotoxins affect the grazing and viability of the calanoid copepod Eurytemora affinis
- 2008
-
Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 361, s. 191-202
-
Tidskriftsartikel (refereegranskat)abstract
- The calanoid copepod Eurytemora affinis from the northern Baltic Sea was exposed to cell-free filtrates of the toxic haptophyte Prymnesium parvum as well as to cell mixtures of P. parvum and Rhodomonas salina. To test the effects of P. parvum exudates and allelopathy on selective grazers, copepods were incubated (1) in increasing concentrations of cell-free filtrates of P. parvum in the presence of good food (R, salina), (2) in 1:1 cell mixtures at 2 cell concentrations of P. parvum and R. salina and (3) in R. salina cell suspension, which was used as a control for good-quality food. P. parvum cultures were grown in nutrient-balanced (+NP) or limited (-N or -P) media to obtain different levels of toxicity. Survival, ingestion, faecal pellet production rates and egg production were measured over 3 d, together with measurements of P. parvum toxicity (hemolytic activity) (HA). Most of the copepods incubated in high-filtrate concentrations died or became severely impaired, although (HA) in filtrates was under the detection limit. Further, the ingestion and faecal pellet production rates were suppressed in the highest filtrate concentrations in nutrient-limited treatments. Higher cell density in cell mixtures resulted in significantly lower faecal pellet production, although survival remained high. Our results show that HA is not a good overall indicator of the total harmful effects of P. parvum on grazers. Besides monospecific P. parvum diets, filtrates and cell mixtures have negative effects on grazers, and these effects are stronger under nutrient-depleted conditions; however, the presence of good-quality food lowers harmful effects for copepods. The negative effects caused either by direct intoxication or by food limitation following from strong allelopathic effects of P. parvum on other components of nano- and microplankton suggest that P. parvum blooms have a realistic potential to be deleterious for copepod secondary production, irrespective of the presence of alternative food sources.
|
|
| 4. |
- Sopanen, S, et al.
(författare)
-
Toxic haptophyte Prymnesium parvum affects grazing, survival, egestion and egg production of the calanoid copepods Eurytemora affinis and Acartia bifilosa
- 2006
-
Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 327, s. 223-232
-
Tidskriftsartikel (refereegranskat)abstract
- Nitrogen- and phosphorus-depleted or NP-balanced toxic haptophyte Prymnesium parvum was fed to 2 dominant copepod species of the northern Baltic Sea (Eurytemora affinis and Acartia bifflosa), and their ingestion, egg and faecal pellet production rates and mortality were measured. The copepods were incubated in 5 different cell concentrations of P. parvum for 3 consecutive days; the cryptophyte Rhodomonas salina was used as a control for non-toxic, nutritionally high-quality food. Toxicity (haemolytic activity) of P. parvum was measured before and after the incubations. The haemolytic activity of R parvum was the highest in cultures grown under nutrient deficiency. The toxicity decreased after 1 d incubation in all treatments, in both the presence and absence of copepods. Neither of the copepod species ingested R parvum, irrespective of the nutrient treatment (toxicity) or cell concentration, and the pellet and egg production rates were correspondingly low. Although there was no significant increase in mortality in P. parvum treatments, copepods that were exposed to P. parvum in any concentration or nutrient treatment soon became inactive. It was evident that the toxicity of even nutrient-replete P. parvum had an indirect and sublethal influence on copepods, although this could not be measured as short-term increased mortality. Our results suggest a strong reduction in secondary production of copepods in an event of a P. parvum bloom.
|
|
| 5. |
- Uronen, P, et al.
(författare)
-
Allelopathic effects of toxic haptophyte Prymnesium parvum lead to release of dissolved organic carbon and increase in bacterial biomass
- 2007
-
Ingår i: Microbial Ecology. - : Springer. - 0095-3628 .- 1432-184X. ; 54:1, s. 183-193
-
Tidskriftsartikel (refereegranskat)abstract
- The haptophyte Prymnesium parvum has lytic properties, and it affects coexisting phytoplankton species through allelopathy. We studied the effect of P. parvum allelo-chemicals on the lysis of the nontoxic and nonaxenic cryptomonad Rhodomonas salina and the consequent release of dissolved organic carbon (DOC). Changes in production, cell density, and biomass of associated bacteria were measured over 12 h. Six different combinations of P. parvum and R. salina cultures, their cell-and bacteria-free filtrates, and growth media as controls were used in the experiments. When P. parvum and R. salina cells were mixed, a significant increase in DOC concentration was measured within 30 min. Bacterial biomass increased significantly during the next 6 to 12 h when R. salina was mixed either with the P. parvum culture or the cell-free P. parvum filtrates (allelochemicals only). In contrast, bacterial biomass did not change in the treatments without the allelopathic action (without R. salina cells). Blooms of P. parvum alter the functioning of the planktonic food web by increasing carbon transfer through the microbial loop. In addition, P. parvum may indirectly benefit from the release of DOC as a result of its ability to ingest bacteria, by which it can acquire nutrients during limiting conditions.
|
|
| 6. |
- Uronen, P, et al.
(författare)
-
Haemolytic activity and allelopathy of the haptophyte Prymnesium parvum in nutrient-limited and balanced growth conditions
- 2005
-
Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 299, s. 137-148
-
Tidskriftsartikel (refereegranskat)abstract
- Prymnesium parvum (Haptophyceae) was grown in 3 different nutrient treatments in semi-continuous cultures, where the N:P molar ratios were modified to 80:1, 4:1 and 16:1. The nutrient concentrations in the media affected the cellular nutrient content of P parvum. The phosphorus content showed larger flexibility in the cells and determined more the cellular nutrient ratios than nitrogen or carbon. Toxicity was measured as haemolytic activity 14 times during the culturing, All the cultures were toxic during the exponential growth, but toxicity increased in the nutrient limited cultures during semi-continuous dilution. The allelopathic effect of P parvum was examined with low cell densities (final abundance 2 and 5 x 10(3) cells ml(-1)) on cryptomonad Rhodomonas salina. With lower cell density, cell structures of R. salina were damaged in one-third of the cells and the cell density decreased slightly. With higher P. parvum cell density, less than half of the R. salina cells remained in the nutrient limited cultures after 23 h. P. parvum grown in nutrient balanced cultures negatively affected R. salina cells. The cellular N:P ratio, which was scaled to the Redfield ratio, could explain 67 and 75% of the variation in the haemolytic activity and the allelopathic effect, respectively. Our results confirm the hypothesis that nutrient deficiency increases toxicity of P. parvum. The haemolytic activity varied during semi-continuous culturing, but it was significantly dependent on intracellular N:P ratios. Due to the allelopathic effect, formation of a P. parvum bloom may accelerate after a critical cell density is reached when the competing species are eliminated.
|
|
| 7. |
- Samuelsson, Malin, et al.
(författare)
-
RhoB controls the Rab11-mediated recycling and surface reappearance of LFA-1 in migrating T lymphocytes
- 2017
-
Ingår i: Science Signaling. - Washington, DC, USA : American Association for the Advancement of Science (A A A S). - 1945-0877 .- 1937-9145. ; 10:509
-
Tidskriftsartikel (refereegranskat)abstract
- The regulation of cell adhesion and motility is complex and requires the intracellular trafficking of integrins to and from sites of cell adhesion, especially in fast-moving cells such as leukocytes. The Rab family of guanosine triphosphatases (GTPases) is essential for vesicle transport, and vesicles mediate intracellular integrin trafficking. We showed that RhoB regulates the vesicular transport of the integrin LFA-1 along the microtubule network in migrating T lymphocytes. Impairment in RhoB function resulted in the accumulation of both LFA-1 and the recycling endosomal marker Rab11 at the rear of migrating T lymphocytes and decreased the association between these molecules. T lymphocytes lacking functional RhoB exhibited impaired recycling and subsequently decreased surface amounts of LFA-1, leading to reduced T cell adhesion and migration mediated by the cell adhesion molecule ICAM-1 (intercellular adhesion molecule-1). We propose that vesicle-associated RhoB is a regulator of the Rab11-mediated recycling of LFA-1 to the cell surface, an event that is necessary for T lymphocyte motility.
|
|
