Genetic diversity of Microcystis cyanophages in two different freshwater environments

Bacteriophages rapidly diversify their genes through co-evolution with their hosts. We hypothesize that gene diversification of phages leads to locality in phages genome. To test this hypothesis, we investigated the genetic diversity and composition of Microcystis cyanophages using 104 sequences of Ma-LMM01-type cyanophages from two geographically distant sampling sites. The intergenetic region between the ribonucleotide reductase genes nrdA and nrdB was used as the genetic marker. This region contains the host-derived auxiliary metabolic genes nblA, an unknown function gene g04, and RNA ligase gene g03. The sequences obtained were conserved in the Ma-LMM01 gene order and contents. Although the genetic diversity of the sequences was high, it varied by gene. The genetic diversity of nblA was the lowest, suggesting that nblA is a highly significant gene that does not allow mutation. In contrast, g03 sequences had many point mutations. RNA ligase is involved in the counter-host’s phage defense mechanism, suggesting that phage defense also plays an important role for rapid gene diversification. The maximum parsimony network and phylogenic analysis showed the sequences from the two sampling sites were distinct. These findings suggest Ma-LMM01-type phages rapidly diversify their genomes through co-evolution with hosts in each location and eventually provided locality of their genomes.     

Ecological dynamics of the toxic bloom-forming cyanobacterium Microcystis aeruginosa and its cyanophages in freshwater

The abundance of potentially Microcystis aeruginosa-infectious cyanophages in freshwater was studied using g91 real-time PCR. A clear increase in cyanophage abundance was observed when M. aeruginosa numbers declined, showing that these factors were significantly negatively correlated. Furthermore, our data suggested that cyanophage dynamics may also affect shifts in microcystin-producing and non-microcystin-producing populations.     

Diversity of virus-like agents killing Microcystis aeruginosa in a hyper-eutrophic pond

We demonstrated the existence of the diversity of virus-likeagents killing Microcystis aeruginosa in a shallow hyper-eutrophicpond in Japan, but without specific virus isolation, once inOctober and twice in December 2001. The pond water was treatedby chloroform, filtered throughout GF-75 filter (0.3 µm)and then incubated with axenic M. aeruginosa for 7 days. Thecell density of M. aeruginosa decreased 10-fold in the courseof the incubation. Results suggested that the active agent forcell death was virus-like, based upon its size fraction (from30 kDa to 0.3 µm), sensitivity on heat-treatment, andevidence of protein protection of DNA during our extractionprocedure. From our results of pulsed field gel electrophoresis(PFGE) analysis, two or four different-sized DNA bands appearedfrom the culture lysate in each experiment. In total, 10 different-sizedbands (10–90 kb) were observed from the three sample dates,suggesting that multiple virus-like agents killing M. aeruginosaexisted in this pond. To our knowledge, this is the first reportof the existence of virus-like agents with different genomicsize that kill M. aeruginosa.     

Diurnal variation in a fish pond in Seoni,India

Summary The diurnal variation in the water chemistry and the plankton of Budhwari tank Seoni, India, which is a highly productive tank, has been studied after the monsoon. Not much variation from the other tropical waters in the chemistry has been noted. The plankton showed a little diversion from the normal behaviour in tropical fresh waters.     

Grazing impact on the cyanobacterium Microcystis aeruginosa by the heterotrophic flagellate Collodictyon triciliatum in an experimental pond

We estimated the grazing impact of the heterotrophic flagellate Collodictyon triciliatum on the harmful, bloom-forming cyanobacterium Microcystis aeruginosa in an experimental pond during a Microcystis bloom from summer to winter in 2010. For these experiments, we calculated the grazing rates from the digestion rate of C. triciliatum and its food vacuole contents. During the study period, M. aeruginosa exhibited one bloom event with a maximum density of 1.1 × 10⁵ cells ml^?1. The cell density of C. triciliatum fluctuated from below the detection limit to 291 cells ml^?1. The number of M. aeruginosa cells ingested by C. triciliatum food vacuoles ranged between 0.4 and 10.8 cells flagellate^?1, and the digestion rate of C. triciliatum at 25 °C was 0.73 % cell contents min^?1. The grazing rate of C. triciliatum on the M. aeruginosa prey was 0.2–6.9 cells flagellate^?1 h^?1, and its grazing impact was 0.0–25.3 % standing stock day^?1. The functional response of C. triciliatum to the M. aeruginosa prey followed the Michaelis–Menten model of significance (r ² = 0.873, p < 0.001) in our experimental systems, in which the prey concentration varied from 1.0 × 10⁴ to 2.1 × 10⁶ cells ml^?1. The maximum grazing rate was 6.2 prey cells grazer^?1 h^?1, and the half-saturation constant was 1.2 × 10⁵ cells ml^?1. We present evidence that C. triciliatum grazing explained the remarkable decrease in M. aeruginosa cell density in the pond. The present study is the first demonstration of the high potential of protistan grazing on M. aeruginosa to reduce cyanobacterial blooms.     

Diurnal mixed layers and the long-term dominance of Microcystis aeruginosa

The population dynamics of the cyanobacterium Microcystis aeruginosain a hypertrophic, subtropical lake (Hartbeespoort Dam, SouthAfrica) were followed over 4.5 years. We examined the hypothesisthat M.aeruginosa dominated (>80% by volume) the phytoplanktonpopulation up to 10 months of each year because it maintaineditself within shallow diurnal mixed layers and was thus ensuredaccess to light, the major limiting resource. Wind speeds overHartbeespoort Dam were strong enough to mix the entire epilimnionthrough Langmuir circulations only 12% of the time. At othertimes solar heating led to the formation of diurnal mixed layers(z₁) that were shallower (<2 m) than the euphotic zone (z_cu;mean = 3.5 m, range: 0.45–8.4 m) while the seasonal mixedlayer (z_m) was always deeper than z_cu (range: 7–18 m).By means of its buoyancy mechanism M.aeruginosa maintained thebulk of its population within z₁, while non-buoyant speciessank into dark layers. Adaptation to strong light intensitywas implicated from low cellular chlorophyll a content (0.132µg/106 cells) and high I_k (up to 1230 µE m^–2s^–1). Ensured access to light, the post-maximum summerpopulations persisted throughout autumn and winter, despitesuboptimal temperatures, by sustaining low losses. Increasedsedimentation losses caused a sharp decline of the populationat the end of winter each year, and a short (2–3 months)successional episode followed, but by late spring M.aeruginosawas again dominant. The data from Hartbeespoort Dam point outthe importance of distinguishing between z_m and z₁, and showthe profound effect that the daily pattern of z₁ as opposedto the seasonal pattern of z_m, can have on phytoplankton populationspecies composition.     

Diurnal buoyancy changes of Microcystis in an artificially mixed storage reservoir

In a storage reservoir, which is artificially mixed in order to reduce algal and especially cyanobacterial growth, the cyanobacterium Microcystis is still present. The aim of the research was to investigate why Microcystis was able to grow in the artificially mixed reservoir. From the results it could be concluded that the large shallow area in the reservoir allows this growth. The loss of buoyancy during the day was much higher in this shallow part than in the deep part. Assuming that the loss of buoyancy was the result of a higher carbohydrate content, a higher growth rate in the shallow part may be expected. A higher received light dose by the phytoplankton in the shallow mixed part of the reservoir than in the deep mixed part explains the difference in buoyancy loss. A significant correlation between the received light dose (calculated for homogeneously mixed phytoplankton) and the buoyancy loss was found. Apparently, the Microcystis colonies were entrained in the turbulent flow in both the shallow and the deep part of the reservoir. With a little higher stability on one sampling day, due to the late start of the artificial mixing, the loss of buoyancy at the deep site was higher than on the other days and almost comparable to the loss at the shallow site. Although the vertical biomass distribution and the temperature profiles showed homogeneous mixing, the colonies in the upper layers apparently received a higher light dose than those deeper in the water column. Determination of the buoyancy state of cyanobacteria appeared to be a valuable method to investigate the light history and hence their entrainment in the turbulent flow in the water column.     

也西湖噬藻体的分离与鉴定

【背景】噬藻体是一类特异性侵染蓝藻的病毒,广泛存在于淡水和海水水体中,参与调控宿主蓝藻的丰度和种群密度,被认为是潜在的蓝藻水华生物防控工具。但目前的研究多集中于海洋噬藻体,对淡水噬藻体的生物学特性和结构生物学等研究较少。【目的】分离更多种类的淡水噬藻体,为研究淡水噬藻体的三维结构、侵染机制、与宿主的共进化关系,及其在蓝藻水华防治中的应用提供理论基础。【方法】采集中国科学技术大学西校区内景观湖也西湖水华暴发水域的水样,利用液体培养基和双层固体平板法对17种宿主蓝藻进行筛选,通过NaCl-PEG沉淀法和氯化铯密度梯度离心分离和纯化噬藻体,并利用负染电镜观察噬藻体的形态,同时采用梯度稀释法测定裂解液的效价。【结果】发现也西湖的水样可特异性侵染本实验室分离自巢湖的一株拟鱼腥藻Pan。侵染后的裂解液中存在4株形态各异的噬藻体,包括1株短尾噬藻体和3株长尾噬藻体,其中包括首次发现的1株含有非典型长轴状头部结构的淡水噬藻体。【结论】也西湖作为巢湖流域的一个小型水体,具有与巢湖类似的水华蓝藻及其噬藻体分布谱,因此可以用于模拟大型湖泊进行相关分子生态学和生物防控的研究。     

Microcystin composition of an axenic clonal strain of Microcystis viridis and Microcystis viridis-containing waterblooms in Japanese freshwaters

Toxic cyclis heptapeptides (microcystin) in cells of an axenic clonal strain of Microcystis viridis were analyzed quantitatively. Cells from the logarithmic, stationary and death phases of batch culture contained 670, 618 and 372 μg toxic cyclic heptapeptides per g dry cells, respectively. The toxic peptides of the cells from the stationary phase consisted of microcystin RR (65%), microcystin LR (22%), microcystin YR (10%) and microcystin LA (3%). The composition of the toxic peptides changed only slightly through the phases of batch culture. Toxicities and the toxic peptide contents of Microcystis viridis-containing waterblooms in Japanese freshwaters were examined. All samples tested had toxic effects on mice after intraperitoneal injection. The toxic peptides in the samples were composed mainly of microcystin RR (50%) and microcystin LR (30%).     

Decomposition patterns of unprocessed and processed lignocellulosics in a freshwater fish pond

In an attempt to recycle the lignocellulosic wastes like Eichhornia crassipes, Salvinia cucullata and rice (Oryza sativa) straw as manurial inputs in freshwater fish pond ecosystem, a decomposition experiment was carried out in litter bags in an oligotrophic freshwater fish pond environment, with the above mentioned three substrates in unprocessed and microbially processed forms. The loss rates, associated microbial groups, oxygen consumption patterns and other related parameters like carbon, nitrogen, phosphorus, cellulose, hemicellulose and lignin were analysed. The mean daily dry matter loss rates (unprocessed: 10.44>6.97>1.97 and processed: 11.03>8.21>3.67) and oxygen uptake rate (unprocessed: 0.675>0.571>0.568 mg O₂ g^–1 h^–1 and processed: 0.592>0.424>0.407 mg O₂ g^–1 h^–1) in raw and processed substrates were in the sequence Eichhornia > rice straw > Salvinia. The oxygen consumption pattern almost covariated with variations in temperature of pond water, daily dry matter loss rates and fungal counts on substrates. During the decay, the percentage of N and P increased whereas that of C decreased, resulting in lowering of C/N and C/P ratios of the substrates. The structural polymeric fractions like cellulose and hemicellulose decreased along with dry matter whereas the lignin content increased after an initial decrease due to loss of other structural carbohydrates resulting in apparent per cent gain of lignin. A higher number of different heterotrophic bacterial groups was observed in the processed substrates as compared to their raw counterparts. However, cellulolytic bacterial numbers were found to fluctuate through the study period. The fungal load was found to be decreasing gradually as the decay progressed. In this study, bacteria were found to be the prominent microbial group responsible for the decay. The nitrogen-fixing, phosphatase-producing and phosphorus-solubilising bacterial groups were observed to play an important role in lowering the C/N and C/P ratios of the decomposing substrates during decay.     

斯洛维尼亚池塘中大蟾蜍的交配模式

为了解大蟾蜍( Bufo bufo)的配对成功是否与身体大小有关,在蟾蜍产卵之前,我们在斯洛文尼亚捕捉和测量了2 224只成体样本。在这些捕获的个体中, 1 772只为雄性, 452只为雌性,其中355对处于抱对状态。雌性的体长(从吻端到泄殖腔的距离)一般比雄性稍长。无论雄性还是雌性,抱对者的体长均大于未抱对者。抱对的雄性和雌性的体长具有显著的正相关。我们所发现的大小匹配的交配模式,与从其它普通蟾蜍种群得到的结果一致[动物学报51 (3) : 513 -515 , 2005]。     

Diurnal patterns of dopamine release in chicken retina

The retinal dopaminergic system appears to play a major role in the regulation of global retinal processes related to light adaptation. Although most reports agree that dopamine release is stimulated by light, some retinal functions that are mediated by dopamine exhibit circadian patterns of activity, suggesting that dopamine release may be controlled by a circadian oscillator as well as by light. Using the accumulation of the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) in the vitreous as a measure of dopamine release rates, we have investigated the balance between circadian- and light control over dopamine release. In chickens held under diurnal light:dark conditions, vitreal levels of DOPAC showed daily oscillations with the steady-state levels increasing nine-fold during the light phase. Kinetic analysis of this data indicates that apparent dopamine release rates increased almost four-fold at the onset of light and then remained continuously elevated throughout the 12h light phase. In constant darkness, vitreal levels of DOPAC displayed circadian oscillations, with an almost two-fold increase in dopamine release rates coinciding with subjective dawn/early morning. This circadian rise in vitreal DOPAC could be blocked by intravitreal administration of melatonin (10 nmol), as predicted by the model of the dark-light switch where a circadian fall in melatonin would relieve dopamine release of inhibition and thus be responsible for the slight circadian increase in dopamine release. The increase in vitreal DOPAC in response to light, however, was only partially suppressed by melatonin. The activity of the dopaminergic amacrine cell in the chicken retina thus appears to be dominated by light-activated input.     

Diurnal patterns in Scots pine stem oleoresin pressure in a boreal forest

Coniferous tree stems contain large amounts of oleoresin under positive pressure in the resin ducts. Studies in North‐American pines indicated that the stem oleoresin exudation pressure (OEP) correlates negatively with transpiration rate and soil water content. However, it is not known how the OEP changes affect the emissions of volatile vapours from the trees. We measured the OEP, xylem diameter changes indicating changes in xylem water potential and monoterpene emissions under field conditions in mature Scots pine (Pinus sylvestris L.) trees in southern Finland. Contrary to earlier reports, the diurnal OEP changes were positively correlated with temperature and transpiration rate. OEP was lowest at the top part of the stem, where water potentials were also more negative, and often closely linked to ambient temperature and stem monoterpene emissions. However, occasionally OEP was affected by sudden changes in vapour pressure deficit (VPD), indicating the importance of xylem water potential on OEP as well. We conclude that the oleoresin storage pools in tree stems are in a dynamic relationship with ambient temperature and xylem water potential, and that the canopy monoterpene emission rates may therefore be also regulated by whole tree processes and not only by the conditions prevailing in the upper canopy.     

Phytoplankton productivity in a pond of brownish-colored water in a Japanese lowland marsh, Naka-ikemi

To understand the characteristics of the ecosystem in Japanese lowland marsh, we investigated chlorophyll-a (Chl. a), photosynthesis and respiration of a phytoplankton community in a brownish-colored pond in Naka-ikemi marsh, Tsuruga, Fukui Prefecture. Chl. a concentrations and volumetric gross primary production rates ranged between 1.3–57.0 μg Chl. a l⁻¹ and 148–1619 μg C l⁻¹ day⁻¹ during the study period. Higher values of Chl. a and primary production rates were clearly observed from June to September, when the dominant algae were the phytoflagellates, Peridinium (Dinophyceae) and Cryptomonas (Cryptophyceae), with swimming ability. The trophic status of the pond water of Naka-ikemi marsh was defined as being in eutrophic condition based on the biomass and productivity of phytoplankton. However, depths of Z _1% showing the productive layer in this study site were relatively narrower than those observed in the hyper-eutrophic Lake Suwa with frequent cyanobacterial water bloom. Factor-attenuating underwater light intensity in Naka-ikemi marsh was presumed to be colored dissolved organic matter. Thus, not only phytoplankton primary production, but also allochthonous organic matter supplied from the catchment area seems to be the dominant factor in the whole energy budget of the pond. In conclusion, we regarded the pond ecosystem in Naka-ikemi marsh to be in a eutrophic–dystrophic condition.     

Dynamics of microcystin-producing and non-microcystin-producing Microcystis populations is correlated with nitrate concentration in a Japanese lake

Temporal changes in hepatotoxin microcystin-producing and non-microcystin-producing Microcystis aeruginosa populations were examined in Lake Mikata, Japan. To monitor the densities of the total M. aeruginosa population and the potential microcystin-producing subpopulation, we used a quantitative real-time PCR assay targeting the phycocyanin intergenic spacer and the microcystin synthetase gene (mcyA), respectively. During the sampling period, the ratio of the mcyA subpopulation to the total M. aeruginosa varied considerably, from 0.5% to 35%. When surface nitrate concentrations increased, there was a rise in the relative abundance of the mcyA subpopulation. This was a positive correlation with the nitrate concentrations (r=0.53, P<0.05, n=14); whereas temperature and ortho-phosphate had no significant correlation with the presence of mcyA. Our data suggest that high nitrate loading may be a significant factor promoting the growth of the microcystin subpopulations within M. aeruginosa communities in Lake Mikata.     

Diurnal and spatial patterns of Phytoseiidae in the citrus canopy

Phytoseiid mites were sampled in a grapefruit orchard at various times of the day to study their diurnal and seasonal distributions in the tree canopy. Samples were collected on 14, 20 and 28 October 1999 at 2 h intervals from 0600 to 2200 h. Similar samples were collected in a grapefruit orchard at 3 h intervals from 0600 to 2100 h on 9 and 16 March and on 17 and 24 August 2000 for phytoseiid mites. No differences in numbers of phytoseiid motiles were observed among the hours sampled in any of the three months. However, significant differences were observed in the number of phytoseiids per leaf based on location within the tree (eastern, western sides of the canopy or interior). Interior leaves collected in March and August 2000 had higher numbers of phytoseiids than exterior leaves taken from either the eastern or western sides of the tree canopy. Phytoseiids were more abundant in the March 2000 samples (mean = 1.10 phytoseiids/leaf) than in either October 1999 or August 2000 samples (mean = 0.16 and 0.19 phytoseiids/leaf, respectively). Prevalent phytoseiid species were Typhlodromalus peregrinus (Muma) (42.1%) and Iphiseiodes quadripilis (Banks) (50.4%) in October 1999, Typhlodromalus peregrinus (Muma) (76.2%) in March 2000, and Euseius mesembrinus (Dean) (54%) in August 2000.     

Diurnal lighting patterns and habitat alter opsin expression and colour preferences in a killifish

Spatial variation in lighting environments frequently leads to population variation in colour patterns, colour preferences and visual systems. Yet lighting conditions also vary diurnally, and many aspects of visual systems and behaviour vary over this time scale. Here, we use the bluefin killifish (Lucania goodei) to compare how diurnal variation and habitat variation (clear versus tannin-stained water) affect opsin expression and the preference to peck at different-coloured objects. Opsin expression was generally lowest at midnight and dawn, and highest at midday and dusk, and this diurnal variation was many times greater than variation between habitats. Pecking preference was affected by both diurnal and habitat variation but did not correlate with opsin expression. Rather, pecking preference matched lighting conditions, with higher preferences for blue at noon and for red at dawn/dusk, when these wavelengths are comparatively scarce. Similarly, blue pecking preference was higher in tannin-stained water where blue wavelengths are reduced. In conclusion, L. goodei exhibits strong diurnal cycles of opsin expression, but these are not tightly correlated with light intensity or colour. Temporally variable pecking preferences probably result from lighting environment rather than from opsin production. These results may have implications for the colour pattern diversity observed in these fish.