Comments on the diel periodicity of phytoplankton photosynthesis, with an example from the Indian Ocean

The well known diel periodicity of phytoplankton photosynthesis under constant light can be explained, to a large extent, by diel periodicity of the photosynthetic activity per unit of chlorophyll; thus, to the same extent, this rhythm is independent of chlorophyll concentration or biomass, and it reflects an endogenous cycle. On the other hand, the periodicity which results from long term (24 hours) exposures under "simulated in situ" conditions belongs to a quite different type. Both phenomena are discussed here on the basis of parallel experiments made during cruise 8 of R/V "Anton Bruun" in the Mozambique Channel (International Indian ocean Expedition)

Diversity and distribution of the dinoflagellates Brachidinium, Asterodinium and Microceratium (Brachidiniales, Dinophyceae) in the open Mediterranean Sea

Brachidiniacean dinoflagellates have been investigated in the open waters of the Mediterranean Sea, along a transect from the south of France to the south of Cyprus (20 June–18 July 2008). Brachidinium and Karenia papilionacea often co-occurred, B. capitatum predominating in the surface waters. The highest abundance of Brachidinium were found in the upper 25min the western Mediterranean with a maximum (24 cells L–1) at a depth of 5 m in the Balearic Sea. Asterodinium (up to 4 cells L–1) was recorded below of deep chlorophyll maxima. The genus Microceratium, only known from the tropical Indo-Pacific region, is reported for the first time in the Mediterranean Sea. Microceratium was found below 100min the eastern Mediterranean Sea, with the highest abundance of 8 cells L–1 at 125 m depth, in the Levantine Basin. This study also illustrates for the first time specimens under the division of Brachidinium and Microceratium. This first occurrence of Microceratium in the Mediterranean Sea should be considered an indicator of climate warming. However, it should not be considered a non-indigenous taxon. Microceratium is the \u27tropical morphotype\u27, the adaptation of a local species (a life stage of Karenia – Brachidinium – Asterodinium) to the tropical environmental conditions that prevail in summer in the open Mediterranean Sea

Some size relationships in phytoflagellate motility

Data from the literature are used to assess some hypothesised adaptive advantages of the flagellate life form among phytoplankton. Possible advantages include increased nutrient uptake by movement through a homogeneous medium as opposed to exploitation of spatial hetrogeneity of the environment. Maximal migrational amplitudes and maximal swimming velocities of phytoflagellates were compared to body size. Both were found to increase with size. Relative amplitudes and relative velocities, however, were found to decrease with size. Hydrophysical considerations show that additional gain of nutrients by swimming through a homogeneous medium is only minimal for small flagellates at their attainable swimming velocities. It is suggested that exploitation of environmental heterogeneity in nutrient distribution may be one of the most important advantages for flagellates over coccoid algae

Dynamics of an intense diatom bloom in the Northern Antarctic Peninsula, February 2016

Diatoms are considered the main base of the Southern Ocean food web as they are responsible for more than 85% of its annual primary production and play a crucial role in the Antarctic trophic structure and in the biogeochemical cycles. Within this context, an intense diatom bloom reaching > 45 mg m−3 of chlorophyll a was registered in the Northern Antarctic Peninsula (NAP) during a late summer study in February 2016. Given that nutrient concentrations and grazing activities were not identified here as limiting factors on the bloom development, the aim of this study was to evaluate the effect of water column structure (stability and upper mixed layer depth) on the phytoplankton biomass and composition in the NAP. The diatom bloom, mainly composed by the large centric Odontella weissflogii (mostly > 70 μm in length), was associated with a local ocean carbon dioxide uptake that reached values greater than −60 mmol m−2 d−1. We hypothesize that the presence of a vertically large water column stability barrier, just below the pycnocline, was the main driver allowing for the development of the intense diatom bloom, particularly in the Gerlache Strait. Contrarily, a shift from diatoms to dinoflagellates (mainly Gymnodiniales < 20 μm) was observed associated with conditions of a highly stable thin layer. The results suggest that a large fraction of this intense diatom bloom is in fast sinking process, associated with low grazing pressure, showing a crucial role of diatoms for the efficiency of the biological carbon pump in this region

Antikinetoplastid SAR study in 3-nitroimidazopyridine series: identification of a novel non-genotoxic and potent anti-T. b. brucei hit-compound with improved pharmacokinetic properties

To study the antikinetoplastid 3-nitroimidazo[1,2-a]pyridine pharmacophore, a structure-activity relationship study was conducted through the synthesis of 26 original derivatives and their in vitro evaluation on both Leishmania spp and Trypanosoma brucei brucei. This SAR study showed that the antitrypanosomal pharmacophore was less restrictive than the antileishmanial one and highlighted positions 2, 6 and 8 of the imidazopyridine ring as key modulation points. None of the synthesized compounds allowed improvement in antileishmanial activity, compared to previous hit molecules in the series. Nevertheless, compound 8, the best antitrypanosomal molecule in this series (EC50 = 17 nM, SI = 2650 & E° = -0.6 V), was not only more active than all reference drugs and previous hit molecules in the series but also displayed improved aqueous solubility and better in vitro pharmacokinetic characteristics: good microsomal stability (T1/2 > 40 min), moderate albumin binding (77%) and moderate permeability across the blood brain barrier according to a PAMPA assay. Moreover, both micronucleus and comet assays showed that nitroaromatic molecule 8 was not genotoxic in vitro. It was evidenced that bioactivation of molecule 8 was operated by T. b. brucei type 1 nitroreductase, in the same manner as fexinidazole. Finally, a mouse pharmacokinetic study showed that 8 displayed good systemic exposure after both single and repeated oral administrations at 100 mg/kg (NOAEL) and satisfying plasmatic half-life (T1/2 = 7.7 h). Thus, molecule 8 appears as a good candidate for initiating a hit to lead drug discovery program

Phytoplankton across Tropical and Subtropical Regions of the Atlantic, Indian and Pacific Oceans

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