The effect of microcystin on some physio-biochemical characteristics of Synechococcus elongatus

In China, lake eutrophication is serious. Many lakes are close to death because receiving too big amounts of polluted water. Recently, heavy blooms frequently occured in Dianchi Lake and Microcystis is the dominant species in the bloom, and in many cases, when appeared in the lake, forms a continuous bloom all along the year, eliminating quite all the other species. Microcystis produces a family of related cyclic hepatopeptides ( microcystins, MC). These toxins are severely hepatotoxic, produced in Microcystis cells and released into water body when algal cells were broken. Most investigations about the toxicity of the microcystins are focused on animals and higher plants. To our knowledge, few studies have been made on the possible effects of microcystins on algae, which are equally important as primary producers in the whole ecosystem. In this study, We chose the unicellular Synechococcus elongatus (one of the most studied, and geographically most distributed, cyanobacteria in the picoplankton) as test material and investigated the toxicological effects of MC-RR on it. For this purpose, some physio-biochemical parameters (cell optical density, chlorophyll fluorescence( Fv/Fm), pigment content( chlorophyll, phycocyanin, soluable protein content, soluable and insoluable carbohydrate content) were tested in algal cells when exposed to 100mug/L microcystin-RR. Microcstin-RR was isolated and purified with the high performance liquid chromatography( HPLC) method. Thereafter, known amount of purified toxin in distilled water was added to test culture flasks in the way to obtain a final toxin concentration in cultures of 100mug.L-1. The results showed that the growth of Synechococcus elongatus (shown as optical density) was significantly inhibited compared with the controls. After exposure to the toxin, the OD665 were lower than those of the controls from (lay 2 to day 10. The OD665 of the control kept in a increasing tendency but that of the toxin-treated decreased on day 8, which meant that the algae had came into death phase in advance. At the same time, a difference in chlorophyll flurorescence(the efficiency of excitation capture by open photo system U (PS U)reaction centers, expressed as Fv/Fm) also appeared. Fv/Fm of the controls kept at a stable high level. In constrast, that of the toxin-treated algae decreased quickly from day 4. The results also demonstrated that toxin treatment could cause the changes of some biochemical characters. For example, the content of soluable protein and soluable, insoluable carbohydrate all reduced after toxin exposure. Alough the content of chlorophyll and phycocyanin of the toxin-treated algae decreased, the ratio of PC/Chl was higher than that of the control. From th present study we could infer the possible toxicological mechanism of microcystin-RR on the cyanobacterium Synechococcus elongatus. Microcystin could inhibit the photosynthetic ability and the inhibition may cause the lack of nutrition( protein, carbohydrate) the decrease of the biochemical reactions and the cell division rate. As a result the growth of the algae was significantly influenced. These results also suggested that microcystins could cause lethal effect on competitive algae and microcystins maybe play a role in phytoplankton succession and population regulation

Cloning and characterization of the fecC gene necessary for optimal growth under iron-deficiency conditions in the cyanobacterium Anabaena sp. PCC 7120

The fecC gene encoding a putative iron (III) dicitrate transporter was cloned from nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120, and inactivated. The mutant grows normally in medium with NO3-, NH4+ or without combined nitrogen. But in iron-deficient medium, the mutant grows slowly. Photosynthetic properties were compared between the mutant and the wild type strain, the content of photosynthetic pigments in the mutant is lower than that of the wild-type. The results of RT-PCR experiments show that the fecC gene is expressed under iron-deficient conditions, but is not expressed under iron-replete conditions. These results revealed that fecC gene product is required for optimal growth under iron-deficient conditions in Anabaena sp. PCC 7120

Ecological meaning and bloom controlling of different density of Silver carp followed with Potamogeton crispus in enclosures

As we know, Silver carp ( Hypophthalmichthys molitrlx) could decrease the biomass of the blue-green algae and have effect on species composition of phytoplankton, but different environment needs different density of Silver carp to control the cyanobacterial bloom. Dianchi lake is situated at Yungui Plateau,and the environment of it is different from other lakes. So the experiment was carried out. In this study, four enclosures in the same size, with an area of 100m2 and a depth of 85cm, and sediment inside,were constructed near Dianchi Lake. And the water inside the enclosures came from the surface of Dianchi lake. Three enclosures were cultured with 100g/m3 , 75g/m3 and 50g/m3 of biomass of Silver carp respectively, and tile left one was as control. During two months, the Chla. of phytoplankton were decreasing and the SD of the water were improving in enclosures cultured with Silver carp. The enclosure with 75g/m3 of Silver carp improved the ecology well. Through putting the fish into the enclosures, the outbreaking of the cyanobacterial bloom was controlled, the dominant species of algae changed, and the biodiversity of phytoplankton increased. In order to study the effects of the Potamogeton crispus L. followed with Silver carp on the ecology of the enclosures. Continual experiment was done. After culturing the fish for two months,the enclosures which had-been cultured with Silver carp were planted with Potamogeton crispus L. and the aquatic plants in enclosure with 75g/m3 of Silver carp grew better than in others, the zooplankton appeared with large amounts, and the SD of the water increased more

Advance in Study on the Ecotoxicological Effect of Microcystins against Microorganisms

Microcystins (MCs), a kind of cyclic heptatoxins produced by numerous cyanobacterial species in eutrophic surface waters, have received increasing worldwide concern in the last decades due to their toxic potential. MCs are also the common algal toxin in the process of water eutrophication and cyanobacteria bloom, and are the most toxic and abundant species. According to the latest progress of ecotoxicology of microcystin on microorganisms (including micro-phytoplankton, bacteria, fungi), the formation of microcystins, physical and chemical properties and the main toxic effects on microorganisms were reviewed, and the research direction were also prospected

Co-effect of doubled CO2 and salinity on some physiological characteristics of Aphanizomenon flos-aquae

Aphanizomenon flos-aquae bloom appears regularly nearly at March in recent years. In order to investigate the response of the cyanobacterium A. flos-aquae to the combination of doubled CO2 concentration and salinity, an experiment was carried out. Growth rate, photosynthesis, maximal electron transport rate (ETRmax), the ratio of photosynthetic pigment chlorophyll a to phycocyanin (Chla/PC) and malondialdehyde (MDA) levels of A. flos-aquae were analyzed. The results demonstrated that salt stress caused decrease in A. flos-aquae growth by disrupting physiological processes, especially photosynthesis. Increased salinity lowered ETRmax. MD content was increased when salinity elevated. And higher salinity has more distinct effect. Growth rate, ETRmax and Chla/PC could be enhanced by elevated CO2 concentration, while doubled CO2 reduced MDA content

Studies on detoxification techniques of toxic algal powder of Microcystis

The harmful algal blooms( HABs) continually occurred in Dianchi Lake in recent years, and the harmful microcystis aeruginosa is the dominant species. In the project on the control of HABs in Dianchi Lake, gathering the microcystis with machine is now used on a large scale. The bloom of Microcystis has high protein content and a big amount of biomass, and it can be used as the raw material of fertilizer in the agricultural production. Since microcystins produced by Microcystis are very difficult to degrade, the utilization of the raw materials is restricted. Furthermore, if the removal or degradation of microcystins can' t be carried out in time, the possible risk of microcystins to environment will inevitable. Thus the detoxication and safe treatment of microcystis powder is necessary. In order to detoxicate the algal powder of Microcystis harvested from Dianchi Lake, three methods, the pH value adjustment, NaClO treatment and O3 treatment, were applied to deal with the algal powder. We measured the effect of detoxification and the loss of protein after the treatments. The result showed that the former two methods(the pH value adjustment and NaClO treatment) didn't work well. With pH adjustment, the detoxication rate of the algal powder was 50%-66%, while it was 77% when NaClO treatment was used. The disadvantage of this method is that the application of a big amount of chemicals will cause environmental pollution. However, when 150mg/ g Of O3 was applied for per gram of dry algal powder, we found that it can detoxificate the algal powder in a short time and have a good effect. So. this method has a good prospect in practice