Toxicity Of Brown Flagellates To Clathrates In Different Vegetative Modes

As an important algae predator, Ochromonas in the freshwater planktonic communities plays a very important role in the energy transmission and biochemical cycle. Toxic compounds produced by many phytoplankton taxa are known to have negative effects on competitors (allelopathy),anti-predatory effects on grazers (mortality or impaired reproduction). Since the 1960s, chrysomonads in the genera Poterioochromonas and Ochromonas have been known or suspected to produce toxins. It was reported that some toxic substances extracted from mixotrophic golden algae (e.g. Poterioochromonas, Ochromonas) are toxic to fish or have antibiotic effects). Toxicity has been demonstrated for several species and strains, i.e. Ochromonas danica, Ochromonas minuta, Ochromonas sociabilis and other Ochromonas spp. and Poterioochromonas malhamensis strains L933/1A-C. Antagonistic chemical interactions can have substantial effects on pelagic community and ecosystem dynamics, especially if toxic species are sufficiently abundant that harmful algal blooms occur. In addition to ecological consequences, harmful algal blooms can have serious economic consequences and prevent both commercial and recreational use of water bodies. Microcystis aeruginosa that can produce toxin is the widely distributed species in harmful algal blooms, and its toxins can inhibit the eukaryotic protein phosphorylation and have toxic effect on the predator. It results not only the aquatic organisms die, but also some human diseases. On the other hand, Microcystis aeruqinosa can form powerful colonies to prevent the feeding of predoters, and zooplankton is hard to live well on it due to the low contents of long chain unsaturated fatty acids and sterol algal cells. Ochromonas sp. and Poterioochromonas sp. can strongly ingest single-celled Microcystis aeruginosa, which led to the decrease of the Microcystis aeruginosa biomass rapidly, and the cyanobacteria toxin do not have negative effect on predators. A large number of instances show that mixed nutrition Ochromonas sp. is an important component in algae, which can be a link between Microcystis aeruqinosa and the next trophic level in material circulation and energy transmission. Mixotrophic flagellates are important constituents of many pelagic food webs where they contribute to both primary and secondary production. Ochromonas species are widely distributed in all kinds of fresh water, and are able to grow well under the conditions of autotrophic, mixotrophic and heterotrophic cultures, this high plasticity in the metabolic model is considered to be adaptive to the changing stress environment.Although photosynthesis is apparently not a major energy source of for many mixotrophs, it may allow these taxa to persist during periods when other sources carbon are unavailable, Photo-autotrophy is usually not the main nutrition mode to obtain energy source for mixotrophic flagellates, and some are mainly use the other source when the favourable carbon resource is limited. Heterotrophic and mixotrophic flagellates are the main component in the planktonic food web. Mixotrophic flagellates obtain energy not only depending on the chloroplast for photosynthesis but also prey bacteria, algae and other organic material to for the growth and reproduction. It is interesting to note that the mode of nutrition of mixotrophic is related to toxin-producing mechanisms. So, we study the toxicity of mixotrophic flagellates to the potential of plankton in the food web. We mainly test whether it is potential toxic to cladocerans that directly prey it, and then test the effects of mode of nutrition on the level of toxicity. we design the following The experiment was designed as followed:In the experiments, we choose Ochromonas sp., Daphnia magna, Daphnia similoides, Moina micrura and Ceriodaphnia cornuta as the experimental organisms, and each treatment lasts two weeks or so. We explore the toxicity of a species of Ochromonas under the nutrition mode of autotrophic, heterotrophic and mixotrophic to four cladocerans respectively.In addition, to test whether the filtrates have toxic effects on cladocerans, we exposed four cladocerans to the filtrates of Ochromonas cultured in chemostats under three different nutritional regimes respectively. The survival conditions of Ochromonas were observed and noted in time. The specific experimental results are as follows:(1) The autotrophic Ochromonas can only rely on their own photosynthesis to obtain energy to survive. The cladocerans is no significant difference in survival of cladoceras between treatment and control group when Ochromonas concentration is under 104 cells ml-1. They were all died after 13 and 12 days respectively, but grew well in Scenedesmus obliquus groups. Daphnia similoides all dead in 14 days and Moina micrura in 11 days, Ceriodaphnia cornuta in 9 days. However, in the wheat medium we find different phenomenons in autotrophic, heterotrophic(dark) and mixotrophic (light).According to the results of the experimental group of D. magna, they all died after 6 and 7 days respectively, whereas those in the control group (hungry) were dead in 12 days. Both the heterotrophic and mixotrophic Ochromonas have toxic effects to D. magna. Based on the two-way ANOVA, there is no significant difference between the two groups, and the similar phenomenon also was found in the proposed Daphnia similoides, Moina micrura and Ceriodaphnia cornuta feeding on mixotrophic Ochromonas. Filtrates had no toxic effects. It is presumed that so the toxic substance may not be released into the water, but only exists in the cell.(2) In this experiment we designed different concentrations of mixotrophic Ochromonas of 8×102 cells mL-1/,5×103 cells mL-1,2×104 cells mL-1×104 cells mL-1 and 5×105 cells mL-1 respectively.10 young aged D. magna were added in each treatment. It was found that at the low concentrations of 8×102 cells mL-1 or 5×103 cells mL-1 and without the other good food sources, D. magna grew slowly and were negatively affected. When the Ochromonas concentrations increased to 104 cells mL-1,the Ochromonas mortality rate is much higher than those in the control hungry group, and death appeared on the second day. It is proved that toxicity effect of the mixotrophic Ochromonas on D. magna is related to its concentration. We also found that on condition that the Ochromonas concentration is low and good food is supplied, the D. magna will grow and produce well. However, it still has sublethal effects on D. magna even though the good food source was supply in the high Ochromonas concentration group. This suggested toxic effects of the mixotrophs Ochromonas on the D. magna.(3)In this experiment, different ages(1,3,5, and 7-day-old) of D. magna were used, and each group contained 20 individuals the medium with mixotrophic Ochromonas. The results showed that different ages D. magna were all dead in 5 days, almost all the control group died on the 11th day, The D. magna feeding on Scenedesmus obliquus were in good condition and no death was observed. The 1-day-old, the 3-day-old,5-day-old,7-day-old D. magna died on the second day. Based on the one-way ANOVA, there was no significant difference in survival of D. magna among the different ages groups.