The effects of Daphnia on nutrient stoichiometry and filamentous cyanobacteria: a mesocosm experiment in a eutrophic lake

1. Stoichiometric theory predicts that the nitrogen : phosphorus (N : P) ratio of recycled nutrients should increase when P‐rich zooplankton such as Daphnia become dominant. We used an enclosure study to test the hypothesis that an increased biomass of Daphnia will increase the relative availability of N versus P sufficiently to decrease the abundance of filamentous cyanobacteria. The experiment was conducted in artificially enriched Lake 227 (L227) in the Experimental Lakes Area (ELA), north‐western Ontario, Canada. Previous studies in L227 have shown that the dominance of filamentous, N‐fixing cyanobacteria is strongly affected by changes in the relative loading rates of N and P. 2. We used a 2 × 2 factorial design with the addition or absence of D. pulicaria and high or low relative loading rates of N and P (+NH₄, –NH₄) in small enclosures as treatment variables. If Daphnia can strongly affect filamentous cyanobacteria by altering N and P availability, these impacts should be greatest with low external N : P loading rates. The phytoplankton community of L227 was predominantly composed of filamentous Aphanizomenon spp. at the start of the experiment. 3. Daphnia strongly reduced filamentous cyanobacterial density in all enclosures to which they were added. The addition of NH₄ had only a small impact on algal community composition. Hence, we conclude that Daphnia did not cause reductions in cyanobacteria by altering the N : P ratio of available nutrients. 4. Despite the lack of evidence that Daphnia affected filamentous cyanobacteria by altering the relative availability of N and P, we found changes in nutrient cycling consistent with other aspects of stoichiometric theory. In the presence of Daphnia, total P in the water column decreased because of an increase in P sedimentation. In contrast to P, a decrease in suspended particulate N was offset by an increase in dissolved N (especially NH₄). Hence, dissolved and total N : P ratios in the water column increased with Daphnia as a result of differences in the fate of suspended particulate N versus P. There was minimal accumulation and storage of P in Daphnia biomass in the enclosures. 5. Our experiment demonstrated that Daphnia can strongly limit filamentous cyanobacterial abundance and affect the biogeochemical cycling of nutrients. In our study, changes in nutrient cycling were apparently insufficient to cause the changes in phytoplankton community composition that we observed. Daphnia therefore limited filamentous cyanobacteria by other mechanisms.     

Effects of tropical solar radiation on the motility of filamentous cyanobacteria

Abstract The effects of tropical solar radiation on the motility of the cyanobacteria Anabaena variabilis, Oscillatoria tenuis and two strains of Phormidium uncinatum were studied in Ghana (4.30°N). The percentages of motile filaments were drastically reduced by unfiltered solar radiation. Covering the organisms with various long pass or band pass filters (WG320, GG395 or UG5) revealed that the UV-B, UV-A and visible light components of the solar spectrum were all effective in impairing motility in these organisms. Only partial recovery was observed and only after short exposure times.     

Survival of diazotrophic cyanobacteria in soil

The survival under drough conditions for one year of 12 heterocystous cyanobacterial strains inoculated in three different soil types (silt clay, calcareous clay and silt loam) gave the highest survival (50%) forScytonema 208L.Fischerella 288L andNostoc OP25 also showed significant survival. Moreover, the soils inoculated withFischerella 288L andScytonema 208L had a higher total N content than non-inoculated soils.     

Isolation and characterization of mutants of two diazotrophic cyanobacteria tolerant to high concentrations of inorganic carbon

Diazotrophic heterocystous cyanobacteria Nostoc calcicola and Anabaena sp. ARM 629 were investigated for their ability to grow in presence of sodium bicarbonate (NaHCO3) or carbon dioxide (CO2) under cultural conditions. Maximum growth was observed in 75 mM NaHCO3 and 5% CO2 in N. calcicola and Anabaena ARM 629, respectively. Although their growth rate declined, N. calcicola and Anabaena sp. could tolerate upto 250 mM NaHCO3 and 20% CO2, respectively. N-methyl-N'-nitro N nitrosoguanidine induced mutants of these cyanobacteria were isolated which showed growth upto 1 M NaHCO3 (N. calcicola) or 50% CO2 (Anabaena sp.) in comparison to their wild types. The mutants also showed cross-resistance to either of the inorganic carbon compounds, which was not observed for wild type. It was concluded that mutants were altered in multiple properties enabling them to grow at elevated levels of inorganic carbon compounds.     

Effects of solar and ultraviolet radiation on motility, photomovement and pigmentation in filamentous, gliding cyanobacteria

Abstract The effects of solar irradiation and artificial UV irradiation on several cyanobacteria ( Anabaena variabilis and two strains of Phormidium uncinatum ) have been studied. Both types of radiation affect the percentage of motile filaments and impair the linear velocity of the organisms. Long term exposure to UV radiation bleaches the photosynthetic pigments as determined by absorption difference spectra. Fluorescence excitation and emission spectra indicate that under ultraviolet radiation the energy transfer from the accessory pigments to chlorophyll is affected. Furthermore the structural integrity of the phycobilisomes seems to be impaired by continuous radiation and the photoreceptor pigments seem to be destroyed.     

Effects of fertilization rate and crop rotation on diazotrophic cyanobacteria in paddy field

Application of chemical fertilizers at the recommended level (medium fertility) or lower stimulated growth of the diazotrophic cyanobacterial population and nitrogenase activity in a paddy field. High fertilizer levels proved to be inhibitory to nitrogen-fixing cyanobacteria indicating that indiscriminate use of chemical fertilizers for a longer period drastically disturbed the natural ecological balance. The rice–mustard–moong (RMM) crop rotation was observed to be more suitable for cyanobacterial nitrogen fixation than rice–wheat–maize rotation. The cropped plots had higher nitrogenase activity than fallow plots. The low fertility coupled with RMM rotation were found to be best suited for promoting nitrogen fixation by cyanobacteria to supply the rice plants. A top dressing of chemical nitrogenous fertilizer drastically suppressed the cyanobacterial nitrogenase activity (ARA) within 12 h; the magnitude of inhibition varied with respect to the cropping system. The inhibition was overcome by the 10th day and the ARA value reached the preapplication value or even higher in the case of low fertility and medium fertility level plots. A regression equation was established to predict nitrogen fixation in a given soil ecosystem.     

Appearance and establishment of diazotrophic cyanobacteria in Lake Kinneret,Israel

1. We propose that the appearance and establishment of Nostocales (cyanobacteria) species of the genera Aphanizomenon and Cylindrospermopsis in the warm subtropical Lake Kinneret (Sea of Galilee, Israel) from 1994 was linked to changes in climate conditions and summer nitrogen (N) availability. 2. From 1994 to 2009, an increase in frequency of events of elevated water temperature (>29 °C) in summer, and to some extent a greater frequency of lower summer wind speed events, affected water turbulence and water column stratification, thus providing better physical conditions for the establishment of these populations. 3. In recent years, N‐depleted conditions in Lake Kinneret in early summer have promoted the development and domination of Nostocales that could gain an ecological advantage owing to their N₂‐fixing capability. 4. Nitrogen fixation rates coincided both with heterocyst abundance and with Nostocales biomass. The N supplied to the lake via nitrogen fixation ranged from negligible quantities when Nostocales represented only a minor component of the phytoplankton community to 123 tonnes when Cylindrospermopsis bloomed in 2005. This high N₂ fixation rate equals the average summer dissolved inorganic nitrogen load to the lake via the Jordan River.     

Characterization of planktonic and biofilm cells from two filamentous cyanobacteria using a shotgun proteomic approach

Abstract

Cyanobacteria promote marine biofouling with significant impacts. A qualitative proteomic analysis, by LC-MS/MS, of planktonic and biofilm cells from two cyanobacteria was performed. Biofilms were formed on glass and perspex at two relevant hydrodynamic conditions for marine environments (average shear rates of 4?s^?1 and 40?s^?1). For both strains and surfaces, biofilm development was higher at 4?s^?1. Biofilm development of Nodosilinea sp. LEGE 06145 was substantially higher than Nodosilinea sp. LEGE 06119, but no significant differences were found between surfaces. Overall, 377 and 301 different proteins were identified for Nodosilinea sp. LEGE 06145 and Nodosilinea sp. LEGE 06119. Differences in protein composition were more noticeable in biofilms formed under different hydrodynamic conditions than in those formed on different surfaces. Ribosomal and photosynthetic proteins were identified in most conditions. The characterization performed gives new insights into how shear rate and surface affect the planktonic to biofilm transition, from a structural and proteomics perspective.     

Grazer control and nutrient limitation of phytoplankton biomass in two Australian reservoirs

1. Grazer and nutrient controls of phytoplankton biomass were tested on two reservoirs of different productivity to assess the potential for zooplankton grazing to affect chlorophyll/phosphorus regression models under Australian conditions. Experiments with zooplankton and nutrients manipulated in enclosures, laboratory feeding trials, and the analysis of in-lake plankton time series were performed. 2. Enclosures with water from the more productive Lake Hume (chlorophyll a = 3–17.5 μg l^–1), revealed significant zooplankton effects on chlorophyll a in 3/6, phosphorus limitation in 4/6 and nitrogen limitation in 1/6 of experiments conducted throughout the year. Enclosures with water from the less productive Lake Dartmouth (chlorophyll a = 0.8–3.5 μg l^–1), revealed significant zooplankton effects in 5/6, phosphorus limitation in 5/6 and nitrogen limitation in 2/6 of experiments. 3. While Lake Hume enclosure manipulations of the biomass of cladocerans (Daphnia and Diaphanosoma) and large copepods (Boeckella) had negative effects, small copepods (Mesocyclops and Calamoecia) could have positive effects on chlorophyll a. 4. In Lake Hume, total phytoplankton biovolume was negatively correlated with cladoceran biomass, positively with copepod biomass and was uncorrelated with total crustacean biomass. In Lake Dartmouth, total phytoplankton biovolume was negatively correlated with cladoceran biomass, copepod biomass and total crustacean biomass. 5. In both reservoirs, temporal variation in the biomass of Daphnia carinata alone could explain more than 50% of the observed variance in total phytoplankton biovolume. 6. During a period of low phytoplankton biovolume in Lake Hume in spring–summer 1993–94, a conservative estimate of cladoceran community grazing reached a maximum of 0.80 day^–1, suggesting that Cladocera made an important contribution to the development of the observed clear-water phase. 7. Enclosure experiments predicted significant grazing when the Cladocera/Phytoplankton biomass ratio was greater than 0.1; this threshold was consistently exceeded during clear water phase in Lake Hume. 8. Crustacean length had a significant effect on individual grazing rates in bottle experiments, with large Daphnia having highest rates. In both reservoirs, mean crustacean length was negatively correlated with phytoplankton biovolume. The observed upper limit of its variation was nearly twice as high compared to other world lakes.     

Behavior of filamentous cyanobacteria in laboratory culture

The observations of a laboratory culture of filamentous cyanobacteria revealed a complex of behavioral responses of their community, which maintain their activity as an integrated entity. A number of structures formed in the course of filament regrouping were revealed and described; their possible structural and functional analogues in eukaryotic organisms were determined. It is assumed that the behavioral reactions of the filaments help to maintain the integrity of the community at the stage prior to the formation of the structural bonds between its elements.     

Morphogenesis in a community of filamentous cyanobacteria

Reversible differentiation was experimentally discovered in a community of modern filamentous cyanobacteria Oscillatoria terebriformis. Splitting of the initially uniform community into differentiated parts (strands, multiradiate aggregates, networks, etc.) occurs only for the duration of a function facilitating the activity of this community as an integral unit. The structures are formed as a result of regrouping of the filaments, without their specialization. A morphologically regulatory system (polygonal network) was found to develop under the impact of extreme factors. The levels of structural organization of filamentous cyanobacteria and multicellular eukaryotes were compared (individual cells in a filament—cell organelles; filaments—individual cells; community—organism), and the similarities and differences in morphogenesis of these groups were analyzed using the data on the embryonic regulation in multicellular eukaryotes. Spatial information in morphogenesis was shown to result not from direct realization of an inherited program but is created by the elements of integral organisms (cells and filaments) in the course of development.     

Behavior of filamentous cyanobacteria in laboratory culture

The observations of a laboratory culture of filamentous cyanobacteria revealed a complex of behavioral responses of their community, which maintain their activity as an integrated entity. A number of structures formed in the course of filament regrouping were revealed and described; their possible structural and functional analogues in eukaryotic organisms were determined. It is assumed that the behavioral reactions of the filaments help to maintain the integrity of the community at the stage prior to the formation of the structural bonds between its elements.     

Glutamine synthetase from the marine cyanobacteria Prochlorococcus spp: characterization,phylogeny and response to nutrient limitation

The regulation of glutamine synthetase (EC 6.3.1.2) from Prochlorococcus was previously shown to exhibit unusual features: it is not upregulated by nitrogen starvation and it is not inactivated by darkness (El Alaoui et al. (2001) Appl Environ Microbiol 67: 2202-2207). These are probably caused by adaptations to oligotrophic environments, as confirmed in this work by the marked decrease in the enzymatic activity when cultures were subjected to iron or phosphorus starvation. In order to further understand the adaptive features of ammonium assimilation in this cyanobacterium, glutamine synthetase was purified from two Prochlorococcus strains: PCC 9511 (high-light adapted) and SS120 (low-light adapted). We obtained approximately 100-fold purified samples of glutamine synthetase electrophoretically homogeneous, with a yield of approximately 30%. The estimated molecular mass of the subunits was roughly the same for both strains: 48.3 kDa. The apparent Km constants for the biosynthetic activity were 0.30 mM for ammonium, 1.29 mM for glutamate and 1.35 mM for ATP; the optimum pH was 8.0. Optimal temperature was surprisingly high (55 degrees C). Phylogenetic analysis of glnA from three Prochlorococcus strains (MED4, MIT9313 and SS120) showed they group closely with marine Synechococcus isolates, in good agreement with other studies based on 16 S RNA sequences. All of our results suggest that the structure and kinetics of glutamine synthetase in Prochlorococcus have not been significantly modified during the evolution within the cyanobacterial radiation, in sharp contrast with its regulatory properties.     

Miniprep DNA isolation from unicellular and filamentous cyanobacteria

A rapid miniprep method for isolation of DNA from 12 strains of cyanobacteria belonging to groups I, III, IV and V is described. The protocol is a modification of the methods of Boyle and Lew [Boyle, J.S., Lew, A.M., 1995. An inexpensive alternative to glassmilk for DNA purification. Trends Genet. 11, 8] and the cetyltrimethyl ammonium bromide (CTAB) extraction method of Sahgai-Maroof et al. [Sahgai-Maroof, M.A., Soliman, K.M., Jorgensen, R.A., Allard, R.W., 1984. Ribosomal DNA spacer-length polymorphisms in barley: Mendelian inheritance, chromosomal location and population dynamics. Proc. Natl. Acad. Sci. USA 81, 8014-80181. The new method is especially useful for obtaining cyanobacterial DNA from unicellular, filamentous and filamentous branched species. The method does not require phenol extraction and the product can be used directly for PCR amplification and restriction digestion.     

The phycocyanin to chlorophyll {alpha} ratio and other cell components as indicators of nutrient limitation in two planktonic cyanobacteria subjected to low-light exposures

The cell composition of the planktonic cyanobacteria, Oscillatoriaagardhii (Gomont) and Oscillatona redekei (van Goor), was comparedfor cultures grown under nitrogen (N) and phosphorus (P) limitation,and light climates which were energy (E) limited (photoperiods3:21 and 6:18 light:dark (LD) and irradiances 12–153 µmolm^–2s^–1). Increases in carbohydrate/protein ratio(CHO/Prot) and declines in chlorophyll a (Cha) and phycocyanin(PC) resulted from N and P limitation. N-, P- and E-limitedcultures could be distinguished on the basis of P content andthe ratio of PC/Cha. The P content range of 0.1–0.55%of ash-free dry weight (AFDW) for P-limited cultures was lowerthan that for N- and E-limited cultures (0.56–2.2 %AFDW).Cultures limited by N were distinguishable from E-limited cellsby lower PC/Cha ratios, ranging from 0 to 4.08, compared to3.9–6.9 for E-limited cells. Under the 3:21 LD cycle,the minimum PC/Cha ratio of E-limited cells was 4.5. Increasesin the CHO/Prot ratios were proportional to the difference betweenthe nutrient-limited growth rate and the non-nutrient-limitedgrowth rate. A comparison of the composition of the two speciesshowed greater accumulation of carbohydrate by O.agardhii undernutrient-limiting conditions, but that O. redekei had higherlevels of protein, chlorophyll a and phycocyanin and, in theabsence of P limitation, higher P contents than O.agardhii.     

Plasmid distribution among unicellular and filamentous toxic cyanobacteria

Plasmid content of 5 hepatotoxin and 2 neurotoxin producing cyanobacterial strains were analyzed. Among the hepatotoxin-producing strains, Microcystis aeruginosa PCC7820, M. aeruginosa M228 and M. aeruginosa UV027 were found to carry plasmids, whereas other hepatotoxin and neurotoxin producing strains did not harbor any plasmids. Correlations were sought between toxicity and the presence of plasmids in toxic cyanobacteria as a function of age. Aged cultures of M. aeruginosa PCC7820 exhibited toxicity and harbored plasmids. In other cyanobacterial strains, plasmids were not detected. The data add to and support the current understanding that plasmids are probably not involved in toxin production in cyanobacteria.Author for Correspondence     

Diversity of diazotrophic unicellular cyanobacteria in the tropical North Atlantic Ocean

We present data on the genetic diversity and phylogenetic affinities of N2-fixing unicellular cyanobacteria in the plankton of the tropical North Atlantic Ocean. Our dinitrogenase gene (nifH) sequences grouped together with a group of cyanobacteria from the subtropical North Pacific; another subtropical North Pacific group was only distantly related. Most of the 16S ribosomal DNA sequences from our tropical North Atlantic samples were closely allied with sequences from a symbiont of the diatom Climacodium frauenfeldianum. These findings suggest a complex pattern of evolutionary and ecological divergence among unicellular cyanobacteria within and between ocean basins.     

Larval food limitation in butterflies: effects on adult resource allocation and fitness

Allocation of larval food resources affects adult morphology and fitness in holometabolous insects. Here we explore the effects on adult morphology and female fitness of larval semi-starvation in the butterfly Speyeria mormonia. Using a split-brood design, food intake was reduced by approximately half during the last half of the last larval instar. Body mass and forewing length of resulting adults were smaller than those of control animals. Feeding treatment significantly altered the allometric relationship between mass and wing length for females but not males, such that body mass increased more steeply with wing length in stressed insects as compared to control insects. This may result in changes in female flight performance and cost. With regard to adult life history traits, male feeding treatment or mating number had no effect on female fecundity or survival, in agreement with expectations for this species. Potential fecundity decreased with decreasing body mass and relative fat content, but there was no independent effect of larval feeding treatment. Realized fecundity decreased with decreasing adult survival, and was not affected by body mass or larval feeding treatment. Adult survival was lower in insects subjected to larval semi-starvation, with no effect of body mass. In contrast, previous laboratory studies on adult nectar restriction showed that adult survival was not affected by such stress, whereas fecundity was reduced in direct 11 proportion to the reduction of adult food. We thus see a direct impact of larval dietary restriction on survival, whereas fecundity is affected by adult dietary restriction, a pattern reminiscent of a survival/reproduction trade-off, but across a developmental boundary. The data, in combination with previous work, thus provide a picture of the intra-specific response of a suite of traits to ecological stress.