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This study investigated the bulk nitrogen isotopic composition and fractionation of marine and freshwater cyanobacteria growing at the expense of atmospheric dinitrogen gas ([N.sub.2]) or nitrate (N[O.sup.-.sub.3]). In agreement with previous studies, cyanobacteria using [N.sub.2] had [delta][sup.15]N values ranging from -2 [per thousand] to -1 [per thousand] and fractionated by 2-3 [per thousand] against atmospheric [N.sub.2]. When grown on N[O.sup.-.sub.3], the analyzed cyanobacteria had a remarkably large range in [delta][sup.15]N, from--14 [per thousand] to 1 [pre thousand], and fractionated by 4-19 [per thousand] relative to the supplied N[O.sup.-.sub.3] Interestingly, several of the N[O.sup.-.sub.3]--utilizing cyanobacteria expressed a nitrogen isotopic signal similar to the one expected for diazotrophic species. Extrapolation to the natural environment indicates that [delta][sup.15]N signals considered to be associated with dinitrogen fixation could also be generated by N[O.sup.-.sub.3] utilization, depending on the isotopic composition of the nitrogen source, the degree of fractionation, and the type of cyanobacterium involved.

To assess variability in carbon isotope signatures ([delta][sup.13]C) between and within populations under natural conditions, with a particular emphasis on colony size, we repeatedly collected planktonic colonies of a freshwater cyanobacterium Gloeotrichia echinulata in two lakes, Pyhajarvi (southwest Finland) and Erken (southeast Sweden). Despite substantial differences in the average [delta][sup.13]C signature of Gloeotrichia between lakes (-6.9 [per thousand] in Pyhajarvi and -20.7 [per thousand] in Erken), a similar, systematic increase in [delta][sup.13]C with colony size was observed in both lakes (of 2 3 [per thousand] in Pyhajarvi and 3-5 [per thousand] in Erken). This suggests declining isotope fractionation with increasing colony size, probably related to diffusion limitation of carbon availability. Temporal variation explained a minor fraction of total subsample variability (range [delta][sup.13]C ~4 [per thousand] in Pyhajarvi and ~6 [per thousand] in Erken). Isotopic [sup.13]C fractionation in Gloeotrichia was likely affected both by carbon source and by colony size.

Lichens are reputedly slow growing and become unhealthy or die in response to supplements of the usual limiting resources, such as water and nitrogen. We found, however, that the tripartite cyanobacterial lichen Lobaria pulmonaria doubled in annual biomass growth after a single 20-minute immersion in a phosphorus solution ([K.sub.2]HP[O.sub.4]), as 'compared to controls receiving no supplemental phosphorus. This stimulation of cyanolichens by phosphorus has direct relevance to community and population ecology of lichens, including improving models of lichen performance in relation to air quality, improving forest management practices affecting old-growth associated cyanolichens, and understanding the distribution and abundance of cyanolichens on the landscape. Phosphorus may be as important a stimulant to cyanobacterial-rich lichen communities as it is to cyanobacteria in aquatic ecosystems. Key words: cyanobacteria; cyanolichen; growth rate; lichen; Lobaria pulmonaria; nitrogen fixation; Oregon, USA; Pacific Northwest, North America; phosphorus; transplant experiment.

Nitrogenase is extremely sensitive to molecular oxygen ([O.sub.2]), and unicellular diazotrophic cyanobacteria separate nitrogen ([N.sub.2])-fixation and photosynthesis to protect nitrogenase from [O.sub.2] produced by photosynthesis. When grown under 12 h light/12 h dark cycles (LD), the marine unicellular diazotrophic cyanobacterium Gloeothece sp. 68DGA expressed the nitrogenase protein and its activity (acetylene reduction activity) only during the dark phase. However, this strain was able to grow diazotrophically under continuous light (CL). To determine whether nitrogenase synthesis and [N.sub.2]-fixation are temporally separated from photosynthesis in the Gloeothece cells that have fully acclimated to CL, the proportion of cells containing nitrogenase (the Fe-protein of nitrogenase) in the culture was measured using an immunocytochemical technique. Cells were grown in a continuous-culture device to maintain constant cell density. Under LD, the cells showed diurnal oscillation of nitrogenase activity, photosynthesis, respiration and the expression and the abundance of the Fe-protein. The oscillation was gradually reduced after the transfer of the cells to CL, and was lost after 23-25 days of cultivation under CL. In CL-acclimated cultures, the Fe-protein was always detected in about 94% of the cells, although the nitrogenase activity was about one-third of the maximum activity in LD-acclimated cultures. These results suggest that synthesis of nitrogenase proceeds without diurnal oscillation in the CL-acclimated cells of Gloeothece sp. 68DGA. As the respiration rate in CL-acclimated culture was as high as the maximum rate observed in LD-acclimated culture, [O.sub.2]-uptake mechanism(s) may have been upregulated to maintain low intracellular p[O.sub.2].

Heterocysts, formed when filamentous cyanobacteria, such as Anabaena sp. strain PCC 7120, are grown in the absence of combined nitrogen, are cells that are specialized in fixing atmospheric nitrogen ([N.sub.2]) under oxic conditions and that transfer fixed nitrogen to the vegetative cells of the filament. Anabaena sp. mutants whose sepJ gene (open reading frame alr2338 of the Anabaena sp. genome) was affected showed filament fragmentation and arrested heterocyst differentiation at an early stage. In a sepJ insertional mutant, a layer similar to a heterocyst polysaccharide layer was formed, but the heterocyst-specific glycolipids were not synthesized. The sepJ mutant did not exhibit nitrogenase activity even when assayed under anoxic conditions. In contrast to proheterocysts produced in the wild type, those produced in the sepJ mutant still divided. SepJ is a multidomain protein whose N-terminal region is predicted to be periplasmic and whose C-terminal domain resembles an export permease. Using a green fluorescent protein translationally fused to the carboxyl terminus of SepJ, we observed that in mature heterocysts and vegetative cells, the protein is localized at the intercellular septa, and when cell division starts, it is localized in a ring whose position is similar to that of a Z ring. SepJ is a novel composite protein needed for filament integrity, proper heterocyst development, and diazotrophic growth. doi:10.1128/JB.00085-07

A physiological, unbalanced model involving the dynamics of intracellular reserves of carbon and nitrogen is presented that describes growth of the marine cyanobacterium Trichdesmium sp. at the expense of [N.sub.2] (diazotropy). The model has indicated that carbon availability is a simple and efficient mechanism to regulate the balance of carbon and nitrogen fixed (C/N ratio) in filaments of cells.

Competition theory has put forward three contrasting hypotheses: Competition for nutrients and light may lead to (i) stable coexistence of species, (ii) alternative stable states, or (iii) competitive exclusion. This paper presents a detailed investigation of competition among phytoplankton species to test these three different hypotheses. First, we developed a competition model combining competition for nutrients and light. Next, we ran monoculture experiments in phosphorus-limited and light-limited chemostats to estimate the model parameters for five freshwater phytoplankton species. Finally, we tested the model predictions in competition experiments, using phosphorus levels ranging from oligotrophic to eutrophic conditions. The population dynamics in the competition experiments were all in agreement with the model predictions. This demonstrates that competition for nutrients and light can be accurately predicted over a wide range of productivities. The experiments revealed that the intensity of competition remained constant or even decreased with increasing nutrient supply. Contrary to expectation, there were no trade-offs between competitive abilities for phosphorus and light. Species that were strong competitors for phosphorus were strong competitors for light as well. Hence, we found neither stable coexistence nor alternative stable states. Ali competition experiments led to competitive exclusion. Furthermore, the physiological traits of the species indicated that, if one would find trade-offs in competitive abilities, competition for phosphorus and light would lead to alternative stable states rather than to stable coexistence. These results suggest that stable coexistence mediated by competition for phosphorus and light is rare, and hence an unlikely explanation for the high biodiversity commonly found in phytoplankton communities. Key words: aquatic ecosystems; biodiversity; competition model; continuous culture; cyanobacteria; green algae; neutral coexistence; phosphate; photosynthesis; productivity gradient; resource competition; stoichiometry.

Research has been conducted on manganese uptake in cyanobacterium Synechocystis sp. PCC 6803. The mechanism of this uptake has been investigated and the results demonstrate that manganese accumulates in the outer membrane, that it is transported via the inner membrane and that the outer membrane allows the cells to overcome transient manganese limitations in the environment.

Although [N.sub.2]-fixing cyanobacteria contribute significantly to oceanic sequestration of atmospheric C[O.sub.2], little is known about how [N.sub.2] fixation and carbon fixation (primary production) interact in natural populations of marine cyanobacteria. In a developing cyanobacterial bloom in the Baltic Sea, rates of [N.sub.2] fixation (acetylene reduction) showed both diurnal and longer-term fluctuations. The latter reflected fluctuations in the nitrogen status of the cyanobacterial population and could be correlated with variations in the ratio of acetylene reduced to [sup.15][N.sub.2] assimilated. The value of this ratio may provide useful information about the release of newly fixed nitrogen by a cyanobacterial population. However, although the diurnal fluctuations in [N.sub.2] fixation broadly paralleled diurnal fluctuations in carbon fixation, the longer-term fluctuations in these two processes were out of phase.

We investigated the effects of addition of dissolved organic matter (DOM) on the growth and chemical composition of Nodularia spumigena cells under conditions of P or N deficiency. Semi-continuous monocultures of N. spurnigena Mertens were established. The cells were exposed to the following treatments: nutrient-sufficient (+NP), nitrogen-deficient without DOM (-N) and with DOM (-NDOM), and phosphorus-deficient without DOM (-P) and with DOM (-PDOM). The -NDOM treatment had the highest N. spumigena cell density (6.1 x [10.sup.7] cells [1.sup.-1]) during the experiment, whereas the P-deficient treatments had the lowest cell numbers (0.53 to 0.66 x [10.sup.7] cells [1.sup.-1]). Both -P and -PDOM treatments yielded P-deficient N. spumigena cells. Dissolved organic nitrogen may provide N and increase N. spumigena yield under conditions of N deficiency. On the other hand, N. spumigena cells did not use DOM as a P source. Received: 19 July 1999 / Accepted: 20 October. 1999

The regulatory influence of the availability of iron, N2 fixation and production was analyzed in the ubiquitous and biogeochemically significant planktonic, diazotrophic cyanobacteria Trichodesmium spp. In naturally occurring and cultured populations, N2 fixation photosynthesis and growth were enhanced by Fe additions as FeCl3 and EDTA-chelated FeCl3.

Viability of electron transfer pathway from pyruvate to flavodoxin and flavodoxin to nitrogenase, in the absence of iron, necessitates the presence of the oxidoreductase enzyme encoded by the nifJ gene of Anabaena 7120. Morphological development of the cyanobacterium Anabaena in an iron-deprived medium leads to the substitution of ferredoxin by flavodoxin. Chromosomal discontinuity yields a mutant. This mutant results due to the nifJ gene. The growth of the mutant in the iron-deficient medium is inhibited.

Results show that the cellular microcystin content of Microcystis strain PCC 7806 varies between 34.5 and 81.4 fg per cell, which is positively correlated with growth rate under photosynthetically active radiation-limited growth. Data indicate a positive effect of light on microcystin production during and up to the maximum growth rate with hihger irradiances causing inhibition.

Research has been conducted on primary sigma factor (PSF) and PSF-like sigma factors . The functions of these PSF and PSF-like sigma factors have been studied via measuring the amount of mRNA produced by sig genes under environmental conditions changing cyanobacteria physiology.

Supply (or loading) ratios of biologically available nitrogen and phosphorus, N:P, have often been suggested as the major determinants for the presence or absence of [N.sub.2] fixing cyanobacteria in aquatic environments. Increasing evidence that some components of the dissolved organic nitrogen (DON) pool can play an active role in supplying N nutrition either directly or indirectly to phytoplankton implies that this source of N must be considered in any attempt to apply the N:P resource ratio approach to predict or explain phytoplankton population composition. For example, the unprecedented bloom of Aphanizomenon ovalisporum that occurred in Lake Kinneret from mid-September through October 1994 derived most of the N required for growth directly or indirectly from DON rather than from [N.sub.2]-fixation. This would suggest that factors other than apparent low N:P ratios were important in causing the outgrowth of the cyanobacteria. The present analysis of the Aphanizomenon bloom in Lake Kinneret emphasizes (1) the need to include the DON pool as a potential source of available N for planktonic microbiota; (2) at least for some cyanobacteria, the presence of heterocysts does not necessarily imply active nitrogen fixation; and (3) the development of diazotrophic cyanobacterial blooms in nature is generally due to a multiplicity of environmental factors.

About 2.4 billion years ago, a surge of oxygen filled Earth's atmosphere, transforming life and the planet. A novel hypothesis explains why this Great Oxidation Event happened several hundred million [...]