Spatial distribution and morphologic diversity of virioplankton in Lake Donghu, China

The spatial distribution and morphological diversity of virioplankton were determined in Lake Donghu which contains three trophic regions: hypertrophic, eutrophic and mesotrophic region. Virioplankton abundance measured by transmission electron microscope (TEM) ranged from 7.7 x 10(8) to 3.0 x 109 ml(-1), being among the highest observed in any natural aquatic system examined so far. The spatial distribution of virioplankton was correlated significantly with chlorophyll a concentration (r = 0.847; P < 0.01) at the sampling sites in Lake Donghu. 76 morphotypes were observed. Most morphotypes have tails, belonging to Siphoviridae, Myoviridae and Podoviridae. The majority of tailed phages in the lake were Myoviridae. Morphotypes which were rarely reported, such as prolate-headed virus-like particles, lemon-shaped virus-like particle, and viruses resembling Tectiviridae and Corticoviridae were all observed in the lake. It is concluded that the high viral abundance might be associated with high density of phytoplankton including algae and cyanobacteria. There was high viral diversity in this eutrophic shallow lake. In addition, cyanophage represented an important fraction of the virioplankton community in Lake Donghu. (c) 2006 Elsevier SAS. All rights reserved.

Population growth and physiological characteristics of microalgae in a miniaturized bioreactor during space flight

A strain of microalgae (Anabaena siamensis) had been cultured in a miniaturized bioreactor during a retrievable satellite flight for 15 days. By means of remote sensing equipment installed in the satellite, we gained the growth curve of microalgae population in space every day in real time. The curve indicated that the growth of microalgae in space was slower than the control on ground. Inoculation of the retrieved microalgae culture showed that the growth rate was distinctively higher than ground control. But after several generations, both cultures indicated similar growth rates. Those data showed that algae, can adapt to space environment easily which may be valuable for designing more complex bioreactor and controlled ecological life support system in future experiment. (C) 2006 Elsevier Ltd. All rights reserved.

Seasonal variation of virioplankton in a eutrophic shallow lake

Lake Donghu is a typical eutrophic freshwater lake in which high abundance of planktonic viruses was recently revealed. In this study, seasonal variation of planktonic viruses were observed at three different trophic sites, hypertrophic, eutrophic, and mesotrophic regions, and the correlation between their abundances and other aquatic environmental components, such as bacterioplankton, chlorophyll a, burst size, pH, dissolved oxygen, and temperature, was analyzed for the period of an year. Virioplankton abundance detected by transmission electron microscope (TEM) ranged from 5.48 x 10(8) to 2.04 x 10(9) ml(-1) in all the sites throughout the study, and the high abundances and seasonal variations of planktonic viruses were related to the trophic status at the sampled sites in Lake Donghu. Their annual mean abundances were, the highest at the hypertrophic site (1.23x10(9) ml(-1)), medium at the eutrophic site (1.19x10(9) ml(-1)), and the lowest at the mesotrophic site (1.02x10(9) ml(-1)). The VBR (virus-to-bacteria ratio) values were high, ranging from 49 to 56 on average at the three sampled sites. The data suggested that the high viral abundance and high VBR values might be associated with high density of phytoplankton including algae and cyanobacteria in this eutrophic shallow lake, and that planktonic viruses are important members of freshwater ecosystems.

Using epilithic diatom communities to assess ecological condition of Xiangxi River system

Assessment method for ecological condition of Xiangxi River system was studied by using 13 candidate metrics of epilithic diatom which can reflect conditions in pH, salinity, nitrogen uptake metabolism, oxygen requirements, saprobity, trophic state, morphological character and pollution tolerant capability etc. By one-way ANOVA, the metrics of relative abundance of acidobiontic algae (ACID), freshwater algae (FRESH), high oxygen requirement (HIGH-O), eutraphentic state (EUTRA) and mobile taxa ( MOBILE) were suitable for distinguishing sites in different conditions. Then, the river diatom index (RDI) composed of these five metrics was used to evaluate ecological condition of the river. The results showed that the healthiest sites were in the Guanmenshan Natural Reserve ( with the mean RDI of 79.73). The sites located in tributary of Jiuchong River also owned excellent state (mean RDI of 78.25). Mean RDI of another tributary - Gufu River and the main river were 70.85 and 68.45 respectively, and the unhealthiest tributary was Gaolan River (with mean RDI of 65.64). The mean RDI for all the 51 sites was 71.40. The competence of RDI was discussed with comparison of evaluation results of DAIpo and TDI, it can be concluded that multimetrics is more competent in assessment task.

Detection of extracellular phosphatases in natural spring phytoplankton of a shallow eutrophic lake (Donghu, China)

The species-specific production of extracellular phosphatases in phytoplankton of a subtropical polymictic take was investigated from March to May 2004. Phosphatase activity was detected directly at the site of enzyme action using the enzyme-labelled fluorescence (ELF) technique. Size fractionation of bulk phosphatase activity (PA), concentrations of soluble reactive phosphorus (SRP), chlorophyll a, and phytoplankton composition were determined in parallel. Phosphatase-positive cells were present in every phytoplankton sample; labelled cells were detected in 33 algal taxa, including many chlorophytes, dinoflagellates and some diatoms, but never among cyanobacteria. We recorded an unusual dinoflagellate bloom (Peridiniopsis sp.), of which similar to 25% of the cells were phosphatase-positive. Several populations were partly phosphatase-positive whenever present, while some other species never showed any activity. The production of extracellular phosphatases was not primarily regulated by ambient P concentrations; algae produced these enzymes even if SRP concentrations were high. Moreover, heterotrophic nanoflagellates most probably contributed to the pool of particle-bound PA in some samples.

Ecophysiological characteristics of four intertidal marine macroalgae during emersion along Shantou coast of China, with a special reference to the relationship of photosynthesis and CO2

Intertidal marine macroalgae experience periodical exposures during low tide due to their zonational distribution. The duration of such emersion leads to different exposures of the plants to light and aerial CO2, which then affect the physiology of them to different extents. The ecophysiological responses to light and CO2 were investigated during emersion in two red algae Gloiopeltis furcata and Gigartina intermedia, and two brown algae Petalonia fascia and Sargassum hemiphyllum, growing along the Shantou coast of China. The light-saturated net photosynthesis in G. furcata and P. fascia showed an increase followed by slightly desiccation, whereas that in G. intermedia and S. hemiphyllum exhibited a continuous decrease with water loss. In addition, the upper-zonated G. furcata and P. fascia, exhibited higher photosynthetic tolerance to desiccation and required higher light level to saturate their photosynthesis than the lower-zonated G. intemedia and S. hemiphyllum. Desiccation had less effect on dark respiration in these four algae compared with photosynthesis. The light-saturated net photosynthesis increased with increased CO2 concentrations, being saturated at CO2 concentrations higher than the present atmospheric level in G. furcata, G. intermedia and S. hemiphyllum during emersion. It was evident that the relative enhancement of photosynthesis by elevated CO, in those three algae increased, though the absolute values of photosynthetic enhancement owing to CO2 increase were reduced when the desiccation statuses became more severe. However, in the case of desiccated P. fascia (water loss being greater than 20 %), light saturated net photosynthesis was saturated with current ambient atmospheric CO2 level. It is proposed that increasing atmospheric CO2 will enhance the daily photosynthetic production in intertidal macroalgae by varied extents that were related to the species and zonation.

Changes in the Phytoplankton community of Lake Donghu since the 1980s

The phytoplankton of Lake Donghu was compared between two periods (i.e., 1982-83 and 1999-2001). During 1982-1983, Lake Donghu was characterized by cyanobacterial blooms, very high summer phytoplankton biomass, and a spring clear-water phase. However, during 1999-2001, the lake was dominated by dinophytes and diatoms and had a relatively low phytoplankton biomass and a very turbid state.. Increased stocking of silver carp and bighead carp during the interim years eliminated cyanobacterial blooms and large-bodied daphnids from the lake, creating favorable conditions for growth of the small-sized algae.

Present status and changes of the phytoplankton community after invasion of Neosalanx taihuensis since 1982 in a deep oligotrophic plateau lake, Lake Fuxian in the subtropical China

Phytoplankton assemblages in the subtrophical oligotrophic Lake Fuxian, the second deepest lake in China, were investigated monthly from September 2002 to August 2003. A total of 113 species belonging to seven phyla were identified, among them, a filamentous green alga, Mougeotia sp., dominated almost throughout the study period and comprised most of the total phytoplankton biomass. Mougeotia sp. has made a substantial development during the past decades: it was absent in 1957, only occasionally present in 1983, increased substantially in 1993, and became predominant in 2002-2003. It is likely that natural invasion of the Taihu Lake noodlefish (Neosalanx taihuensis) has led to a change of dominant herbivorous zooplankton from small to large calanoid, which has increased grazing pressure on small edible algae, and thus has indirectly favored the development of the inedible filamentous Mougeotia sp.

Study on fluorescence emission and synchronous-scan fluorescence spectrea of Nitzschia hantzschiana solution with FE(III)

The characterization of the algal Nitzschia hantzschiana solution with (or without) Fe(III) was carried out using fluorescence emission and synchronous-scan spectroscopy. An emission peak (excited at 440 nm) was observed at 675 nm for Nitzschia hantzschiana solution. The effective characterization method used was synchronous-scan fluorescence spectroscopy (SFS). A wavelength difference (Delta lambda) of 90 nm was maintained between excitation and emission wavelengths. The peak was observed at about 236(ex) nm (326(em) nm) for synchronous fluorescence spectroscopy. Fe(III) was an effective quencher. The relationship between I-0/I (quenching efficiency) and c (concentration of Fe (III) added) was a linear correlation for the algal solution with Fe(III). Effects of pH on synchronous-scan fluorescence intensity were evident.

Growth and antioxidant system of the cyanobacterium Synechococcus elongatus in response to microcystin-RR

Microcystins, one type of the cyanobacterial toxins, show a broad range of hazardous effects on other organisms. Most of the researches on the toxic effects of microcystins have involved in animals and higher plants. Little work, however, has been done on evaluating the mechanisms of microcystin toxicity on algae. In this study, the toxicological effects of microcystin-RR (MC-RR) on the cyanobacterium Synechococcus elongatus were investigated. For this purpose, six physio-biochemical parameters (cell optical density, reactive oxygen species (ROS), malondialdehyde (MDA), glutathione (GSH), glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST)) were tested in algal cells when exposed to 100 mug(-1) microcystin-RR. The results showed that the growth of Synechococcus elongatus ( expressed as optical density) was significantly inhibited compared with the control. At the same time, the treated algae exhibited a pronounced increase in production of ROS and MDA after 6 days exposure to microcystin-RR. Signi. cant changes in GSH levels and GSH-Px, GSH activities were also detected in algal cells, with higher values being observed in the toxin treated algae after 6 days exposure. GST activities in the treated algae exhibited a decline after exposure and rapid augmentation on day 3, thereafter, they kept at a high level when compared to the control group. GSH contents and GSH-Px activities were also significantly raised in the toxin-treated algae cells from day 3, but they showed a sharp decrease on day 4, which was the onward of cell proliferation. These results suggested that oxidative stress manifested by elevated ROS levels and MDA contents might be responsible for the toxicity of microcystin to Synechococcus elongatus and the algal cells could improve their antioxidant ability through the enhancement of enzymatic and non-enzymatic preventive substances.

The toxicities of single-celled Microcystis aeruginosa PCC7820 and liberated M-aeruginosa to Daphnia carinata in the absence and presence of the green alga Scenedesmus obliquus

We evaluated the toxic effect of Microcystis aeruginosa on Daphnia carinata King using survival rate, population growth rate, and body length. When fed Microcystis aerugionsa PCC7820 and liberated colonial Microcystis spp., all D. carinata died within five days. When fed a mixture of M. aeruginosa PCC7820 and the green alga Scenedesmus obliquus, the survival rate, population growth rate, and body length of D. carinata generally increased. The survival rates were all above 80% after ten days. However, with liberated colonial M. aeruginosa, the toxic effect on D. carinata was more pronounced, and only at higher concentration of S. obliquus did that toxic effect abate. Our results indicated that green algae could greatly weaken the toxic effect of cyanobacteria.

Physiological and biochemical microcystin-RR toxicity to the Synechococcus elongatus

Freshwater Microcystis may form dense blooms in eutrophic lakes. It is known to produce a family of related cyclic hepatopeptides (microcystins, MC) that constitute a threat to aquatic ecosystems. Most toxicological studies of microcystins have focused on aquatic animals and plants, with few examining the possible effects of microcystins on phytoplankton. In this study we chose the unicellular Synechococcus elongatus (one of the most studied and geographically most widely distributed cyanobacteria in the picoplankton) as the test material and investigated the biological parameters: growth, pigment (chlorophyll-a, phycocyanin), photosynthetic activity, nitrate reductase activity, and protein and carbohydrate content. The results revealed that microcystin-RR concentrations above 100 mug (.) L-1 significantly inhibited the growth of Synechococcus elongatus. In addition, a change in color of the toxin-treated algae (chlorosis) was observed in the experiments. Furthermore, MC-RR markedly inhibited the synthesis of the pigments chlorophyll-a and phycocyanin. A drastic reduction in photochemical efficiency of PSII (F-v/F-m) was found after a 96-h incubation. Changes in protein and carbohydrate concentrations and in nitrate reductase activity also were observed during the exposure period. This study aimed to evaluate the mechanisms of microcystin toxicity on a cyanobacterium, according to the physiological and biochemical responses of Synechococcus elongatus to different doses of microcystin-RR. The ecological role of microcystins as an allelopathic substance also is discussed in the article. (C) 2004 Wiley Periodicals, Inc.

Cloning and characterization of the gene for UDPGlc dehydrogenase from the cyanobacterium, Microcystis aeruginosa FACHB 905

Using degenerate primers based on conserved regions of the UDP-glucose dehydrogenase (UDPGDH) gene, an initial 476-bp DNA fragment was amplified from the water-bloom forming cyanobacterium, Microcystis aeruginosa FACHB 905. TAIL-PCR and ligation-mediated PCR were used to amplify the flanking regions to isolate an about 2.5-kb genomic DNA fragment. Sequence analysis revealed an ORF encoding a putative 462 amino acid protein, designated Mud for Microcystis UDPGDH. The Mud amino acid sequence is closely related to UDPGDH sequences from cyanobacterium Synechocystis PCC6803 (73% identity, 81% similarity), and bacterium Bacillus subtilis (51% identity and 67% similarity). The cloned mud gene was expressed in Escherichia coli using the pGEX-4T-1 fusion expression vector system to generate a GST-Mud fusion protein that exhibited UDPGDH activity. The cytosolic fraction of M aeruginosa FACHB 905 was subjected to Western analysis with an anti-Mud antibody, which revealed a single band of approximately 49 kD, consistent with the deduced molecular mass of the enzyme. The Mud protein could thus be characterized as a UDP-glucose dehydrogenase, which was a key enzyme for polysaccharide synthesis and has, for the first time, been studied in algae.

Variation of microcystins in a lake for water supply

A site investigation was conducted to correlate the relationships between microcystins (MC) concentration and algal growth in Dianchi Lake in China. Laboratory experiments were undertaken to test the effects of sediment adsorption, photoirradiation and biodegradation on microcystins removal. Bioaccumulation of microcystins was also determined using silver carp fish. It was observed that MC concentrations varied in accordance with algae growth in Dianchi Lake. The results obtained in the laboratory demonstrated that the removal of MC with fresh sediments was less than 10%, photoirradiation removed more than 75% MC within two hours, and the biodegradation needed much longer time to produce substantial degradation of MC. The results suggest that bioaccumulation of microcystins in fish was not significant in Dianchi Lake.

Effects of CO2 concentrations on the freshwater microalgae, Chlamydomonas reinhardtii, Chlorella pyrenoidosa and Scenedesmus obliquus (Chlorophyta)

In order to investigate the possible impacts of increased atmospheric CO2 levels on algal growth and photosynthesis, the influence of CO2 concentration was tested on three planktonic algae (Chlamydomonas reinhardtii, Chlorella pyrenoidosa, and Scenedesmus obliquus). Increased CO2 concentration enhanced significantly the growth rate of all three species. Specific growth rates reached maximal values at 30, 100, and 60 muM CO2 in C. reinhardtii, C pyrenoidosa, and S. obliquus, respectively. Such significant enhancement of growth rate with enriched CO2 was also confirmed at different levels of inorganic N and P, being more profound at limiting levels of N in C pyrenoidosa and P in S. obliquus. The maximal rates of net photosynthesis, photosynthetic efficiency and light-saturating point increased significantly (p<0.05) in high-CO2-grown cells. Elevation of the CO2 levels in cultures enhanced the photoinhibition of C. reinhardtii, but reduced that of C pyrenoidosa and S. obliquus when exposed to high photon flux density. The photo-inhibited cells recovered to some extent (from 71% to 99%) when placed under dim light or in darkness, with better recovery in high-CO2-grown C. pyrenoidosa and S. obliquus. Although pH and pCO(2) effects cannot be distinguished from this study, it can be concluded that increased CO2 concentrations with decreased pH could affect the growth rate and photosynthetic physiology of C. reinhardtii, C. pyrenoidosa, and S. obliquus.