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

Isolation, Identification and Characterization of Blue-green Algae-lysing Strain DC-L14 from Lake Dianchi, China

An algae-lysing strain DC-L14 was isolated from an area with dense blue-green algae in Lake Dianchi, southwestern China and it was identified as Lysinibacillus fusiformis based on 16S rDNA sequence analysis. The toxicity test on mouse primarily showed that the strain was non-toxic. Under the laboratory condition, the strain could cause Microcystis aeruginosa cells to agglomerate, sinking to bottom and becoming yellow. The reduction rate of chlorophyll a after 4 days was 67.2% on an average, with the highest of 70.1% and lowest of 65.5% in the cultures of Microcystis viridis, M wesenbergii, Aphanizomenon flos-aquae and Anubaena flos-aquae. The strongest algae-lytic ability was found at the stable phase of DC-L14 culture, which could reduce chlorophyll a content of M aeruginosa by 82.1% in four days. After centrifugation and sedimentation, the cells of bacteria showed no algae-lytic ability, but the cell-free supernatant displayed the same algae-lytic ability as that of the whole bacteria culture, and the heated bacterial culture showed the highest algae-lytic ability, indicating that some extracellular and thermo-stable substances produced by this strain had the algae-lytic ability, and high temperature possibly reinforced the algae-lytic ability

Effect of water bloom-forming cyanobacterial bio-substances on the growth of submerged macrophyte Ceratophyllum oryzetorum Kom.

The different forms of cyanobacterial bio-substances on the growth and photosynthetic activity of submerged macrophyte Ceratophyllum oryzetorum Kom was investigated in present study. Results showed that all kinds of cyanobacterial bio-substances ould enhance the growth of C. oryzetorum Kom. differently. Compared with the control, the plant length of C. oryzelorum could be increased by all forms of bio-substanees, in which the dry algal material has the strongest effect, while the decomposed material has the lowest. The fresh weight of C. oryzetorum also could be promoted by all kinds of algal bio-substanees, in which the dry algal material and the fresh algal material almost have the same obvious effect, and the decomposed algal material has the lowest, while in control, the fresh weight firstly increased, and then decreased. All forms of cyanobacerial material could promote the increase of branches in C. oryzetorum, in which the fresh algal material has the strongest effect and the dry and decomposed materials lower, while in control, the branches increased also less than the algal material treated groups. The photosynthetic activity expressed by chlorophyll fluorescence suggested that the (try algal material treated C. oryzetorum had the highest activity, and the fresh algae treated one lower, and the decomposed algae and the control treated ones were the lowest. In conclusion, the different forms of cyanobacterial bio-substances could supply nutrients or growth promoters for C. oryzetorum to grow, and at the same time, other growth inhibiters might exist to inhibit the growth of C. oryzetoritm. Factors of promoting and inhibiting worked together, thus resulted in the different promoting effects by different forms of cyanobacterial bio-substances to the growth in C. oryzetorum

Uptake of the cyanobacterial hepatotoxin microcystin-RR by submergent macrophyte Vallisneria natans (Lour.) Hara.

Recently, heavy blooms frequently occured in Dianchi Lake and Microcystis is the main algae involved in blooms. Microcystis produces a family of related cyclic hepatopeptides( microcystins, MC). These toxins are severely hepatotoxic. Most investigations about the toxicity of the microcystins are focused on animals and terrestrial plants. To our knowledge, only a few studies have been made on the possible accumulation of microcystins on aquatic plants. This Paper evaluated the accumulation of MC-RR in Vallisneria natans, which is commonly used as food for fish or crab in some aquaculture places, using ELISA to quantify the amount of the heptotoxin accumulated. The results indicated that the roots and leaves of V. natans seedlings can absorb MC-RR. the amount of toxin accumulated in the roots and leaves of the seedlings is time and dose dependent, and the roots absorbed more toxins than leaves given the same condition.. The absorption peaked after 7d' s exposure to the toxin and maintained this value in leaves, while the toxin in roots still accumulating after 16d's exposure. The maximum amount of toxin accumulated in the roots and leaves is 14.83 +/- 0.12mug/g. FW and 0.32 +/- 0.026mug/g. FW respectively when exposed to the 10mg/L toxin solutions I and the numbers reduced to 0.59 +/- 0.083pg/g. FW and 0.28 +/- 0.016pg/g. FW when the toxin is at the concentration of 0.0001 mg/L. In contrast, the BCF value of the root and shoot increased from 0.13 +/- 0.013 and 0.035 +/- 0.0048 to 5.85 +/- 0.83 and 2.85 +/- 0.16 respectively. The results indicate that Microcystin-RR can accumulate in Vallisneria natans plant and raise the possibility that Microcystins could be thereby transferred into aquatic food web

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

Relationships between monthly variances of iron concentration and physicochemical factors in enclosures of Lake Dianchi

Iron is ail essential trace element for the biological requirements of photoplankton. It can be involved in chlorophyll and phycobilin pigment biosynthesis, in many components of photosynthetic (PSI and PSII) and electron transport systems. and in nitrate assimilation as ail enzyme co-factor( nitrate reductase and nitrite reductase). In recent years, many researchers focus oil effects of iron oil cyanobacterial ecophisiology, but limited experiments have been done. The aim of this study is to find out the relationships between different iron forms and physicochemical factors. From the results we call present some basic evidences for controlling cyanobacterial blooms.Experimental enclosures were used in this study. Three encloseures were devised nearby Like Dianchi, in which we planted aquatic plants and bred fishes except for 1 # enclosure. Aquatic plants were the same in other two enclosures, but the density of fishes was different. In 2 # enclosure and 3 # enclosure, the density of fishes was 100g/m(3) and 75g/m(3), respectively. We sampled periodically from three enclosures and the concentrations of total iron, ferrous iron and Filtered iron(<0.45 mu m) of the water samples were determined. The relationships between the dynamic changes and physical and chemical factors were also analyzed. The results showed that under the conditions of pH 7-9 and water temperature 17.5-20.5 degrees C. photoplankton thrived and up-taked ferrous it-oil so the concentrations of ferrous iron decreased highly. Dissolved oxygen, phosphate and dissolved total phosphate had no significant influences oil the concentrations of ferrous iron and other iron forms. Under serious cyanobacterial bloom. total iron and dissolved iron had no significant variances. while significant relationship between ferrous and population density of phytoplankton was found (r=-0.8391, P<0.05). Based oil the results we call make a conclusion that total iron is not a limiting factor in eutrophic freshwater lakes, but iron bioavailability plays ail important role in waterbloom formation and disappearance

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