The endosymbiotic association between the diatom Hemiaulus and the cyanobacterium Richelia was first observed in the Sea of Marmara in July 2021. The spatial distribution of the host diatom Hemiaulus spp. and the endosymbiont cyanobacterium Richelia intracellularis was investigated along with available physicochemical parameters. Three species of the Hemiaulus genus (H. hauckii, H. membranaceus, and H. sinensis) were morphologically identified in the study area. Hemiaulus hauckii and H. sinensis reached up to 128 × 103 cells L−1 and 38 × 103 cells L−1, respectively, while H. membranaceus was rarely observed. Each Hemiaulus cell contained one Richelia trichome, which had heterocysts at both ends. The surface water temperatures and salinity varied between 23.2°C and 28.5°C, 21.4 and 23.5, respectively. Dissolved oxygen levels ranged from 6.2 to 7.6 mg L−1, while chlorophyll-a concentrations were between 0.3 and 6.8 µg L−1. Nutrient concentrations varied between 0.05 and 0.18 μM for NO3 + NO2–N, 0.04–0.24 μM for NH4–N, 0.02–0.39 μM for PO4–P, and 0.18–1.42 μM for SiO2–Si. This study reveals that the Hemiaulus–Richelia symbiosis may promote the proliferation of diatom populations and may play an important role in nutrient dynamics in nitrogen-limiting environments and in the overall functioning of the marine ecosystem.

Water microbiological and physicochemical characterizations at various depths of aquatic ecosystems are basic requirements in several fields of research. A chief difficulty in hydrobiology, limnology, biological oceanography and water environmental microbiology is that of taking accurate field collections that are representative of the natural environment and population at various depths of aquatic ecosystems. Gathering water/plankton samples in a level just below the surface of the water body upon rising in columns from various depths due to hydrostatic pressure variations provided a simple approach for water and plankton sampling. Based on this approach, several forms of simple devices for water and plankton sampling were developed for water microbiological and physicochemical characterizations at various depths of aquatic ecosystems. The described approach showed less sampling errors in comparison to Van Dorn bottle and was comparable to water pumping but requires no external source of power. The described samplers are inexpensive and can be self constructed.

Photosynthetic responses of rewetted Nostoc flagelliforme to CO2, desiccation, light and temperature were investigated under emersed conditions in order to characterize its ecophysiological behaviour in nature. Net photosynthesis increased to a maximum rate at about 30% water loss, then decreased, while dark respiration always decreased with the progress of desiccation. Light-saturated photosynthesis and dark respiration were significantly reduced at 8 °C, but remained little affected by changes of temperature within the range of 15–35 °C. Photosynthetic efficiency (α) was maximal at the beginning of desiccation and then reduced with increased water loss. Saturating irradiance for photosynthesis was about 194–439 μmol quanta m−2 s−1, being maximal at about 30% water loss. No photoinhibition was observed at irradiances up to 1140 μmol m−2 s−1. Light compensation points were about 41–93 μmol m−2 s−1. Photosynthesis of N. flagelliforme was CO2-limited at the present atmospheric CO2 level. The CO2-saturated photosynthesis increased with increase of irradiance (190–1140 μmol m−2 s−1) and temperature (8–25 °C) and decreased significantly with water loss (0–75%). Photosynthetic affinity for CO2 was sensitive to temperature and irradiance. The CO2 compensation point (Γ) increased significantly with increased temperature and was insensitive to irradiance. Desiccation did not affect Γ values before water loss exceeded 70%. Photorespiratory CO2 release did not occur in N. flagelliforme at the current atmospheric CO2 level.

L'évolution spatio-temporelle de l'activité phosphatase alcaline spécifique (APA) (EC: 3.1.3.1) des peuplements phytoplanctoniques de la retenue de Grangent (Loire) a été étudiée. Cette activité enzymatique est maximale en été (comprise entre 20 et 69,4 μmol P-PO4 3-.h-1.mg-1 au niveau de l'épilimnion) et minimale en automne et au printemps (variant de 0,1 à 10 μmol P-PO4 3-.h-1.mg-1). Elle diminue au fur et à mesure que l'on s'enfonce dans la colonne d'eau et est inversement corrélée à la teneur en orthophosphate du milieu. Par ailleurs, l'activité phosphatasique est étroitement liée aux fleurs d'eau cyanobactériennes. En présence d'une même concentration en orthophosphate, les algues semblent être de meilleures compétitrices que les Cyanobactéries dans l'assimilation du PO4 3- dissous. Les Cyanobactéries ont ainsi davantage recours à l'activité phosphatasique pour disposer du phosphore minéral indispensable à leur métabolisme. Cette différence de comportement dans l'utilisation du phosphore entre les Cyanobactéries et les algues pourrait représenter uncritère explicatif supplémentaire des successions écologiques.

The role of external Ca2+ in the homeostasis of intracellular pH (pHi) of Anabaena sp. strain PCC7120 in response to a decrease in the external pH (pHex) has been studied in cell suspensions. Increase in cytoplasmic pH after acid shock is dependent on the presence of Ca2+ in the medium. The observed Ca2+-mediated alkalization of the cytoplasm depends on the extent of the shift in external pH. Acid pH shifts resulted in an increased permeability of the cytoplasmic membrane to protons, which could be reversed by increasing the concentration of Ca2+ in the medium. Thus, the ability of Ca2+ to increase cytoplasmic pH might be correlated with an inhibition of net proton uptake by increasing concentrations of external Ca2+ under these conditions. This combined response resulted in the generation and maintenance of a larger pH gradient (ΔpH) at acid external pH values. All Ca2+ channel blockers tested, such as verapamil and LaCl3, inhibited the observed Ca2+-mediated response. On the other hand, the Ca ionophore calcimycin (compound A23187) was agonistic, and stimulated both cytoplasmic alkalization and inhibition of net proton uptake. The protonophorous uncoupler carbonylcyanide m-chlorophenyl hydrazone, inhibited this Ca2+-mediated response, whereas monensin, an inhibitor of the Na+/H+ antiporter, had no significant effect. The results of the present study suggest that an influx of Ca2+ from the extracellular space is required for the regulation of cytoplasmic pH in Anabaena sp. strain PCC7120 exposed to low external pH values.

Changes in various cell functions were examined during a shift of the cyanobacterium Anabaena sp. strain PCC7120 to acidic external pH (pHex) in the presence and absence of added calcium. In the presence of 0·25 mM Ca (the standard Ca concentration of the growth medium), growth and O2 evolution were inhibited at pH values lower than 6. The cyanobacterium was unable to maintain a relatively constant internal pH (pHi) at pH 6 and below, which led to acidification of the cytoplasm. In the absence of Ca, the acidification found at acid pH values was even more pronounced. The elimination of Ca did not affect pHi at pHex of 6·5 and above. Increased acidification of the internal cell contents correlated well with a general impairment of growth in Ca-deficient cells exposed to external acid pH values. On the other hand, Ca enrichment of cells grown under acidic conditions resulted in a significant improvement of several physiological processes. The protein pattern of cell extracts of Anabaena sp. strain PCC7120 was altered by acidity. The most significant modifications of the protein profiles induced at low pH were not evident in the presence of high concentrations of Ca. Increasing concentrations of Ca allowed Anabaena sp. strain PCC7120 to perform better at lower pH.

The cyanobacterium Microcystis PCC7806, grown under continuous light, fermented endogenously stored glycogen to equimolar amounts of acetate and ethanol when incubated anaerobically in the dark. In addition, H2, CO2 and some L-lactate were produced. This fermentation pattern differed from that displayed by cells which had been grown under an alternating light/dark (16/8 h) cycle. Such cells produced much more ethanol than acetate, while no lactate was formed. These differences could not be related to the levels of key enzymes of fermentation, which were identical in the two cultures. The cultures grown under continuous light contained twice as much glycogen as the light/dark-grown cells and the former metabolized it at a rate approximately 3 times as fast as the latter culture. Fermentation in the culture grown under continuous light showed low carbon recovery (59–80%) and high oxidation/reduction balance (approximately 1·5). On the basis of calculations of ATP yield it was concluded that this culture was capable of growth driven by fermentation. The increase in structural cell material would account for the missing carbon and reduction equivalents.

Spontaneous mutation of the cyanobacterium Nostoc muscorum to a caesium resistant (Cs+-R) phenotype resulted in severe impairment of its nitrogenase activity, oxygenic photosynthesis, chlorophyll a content and osmotolerance. Among alkali cations only Cs+ or Rb+ restored these physiological processes to an almost normal level. Parent and mutant were similar with respect to Cs+ or Rb+ uptake and accumulation and also to regulation by NH4+. The ions Na+ or K+, at much higher concentration, significantly influenced Cs+ uptake and accumulation in both the mutant and the parent. These findings have important implications for cyanobacteria growing in Cs+-polluted habitats.