Marine Phyto Research Articles

Phage Infection Benefits Marine Diatom Phaeodactylum tricornutum by Regulating the Associated Bacterial Community.

The interaction between marine phyto- and bacterioplankton is regulated by multiple environmental and biological factors. Among them, phages as the major regulators of bacterial mortality are considered to have important impacts on algae-associated bacteria and algae-bacteria relationship. However, little is currently known about the actual impact of phages from this perspective. Here, we revealed that phage infection improved the maximum quantum efficiency of photosystem II of Phaeodactylum tricornutum by regulating the associated bacterial community. Specifically, phage infection weakened bacterial abundance and eliminated their negative effects on the diatom. Unexpectedly, the structure of the bacterial community co-cultured with the diatom was not significantly affected, likely because the shaping effect of the diatom on the bacterial community structure can far outcompete or mask the impact of phage infection. Our results established a link between algae, bacteria, and phages, suggesting that phage infection benefits the diatom by regulating the associated bacterial community.

Dinosaur demise in light of their alleged perennial polar residency

The end-Cretaceous biological crisis is represented by the demise of the non-avian dinosaurs. However, most crucial biologically was the elimination of the photosynthesizing marine phyto- and zooplankton forming the base of the marine food chain. Their abrupt demise attests to sunlight screening darkening the atmosphere for a few years. Alvarez et al. (Science 208:1095–1108, 1980. doi:10.1126/science.208.44) noticed in deep marine end-Cretaceous sediments an anomalous rise in the chemical element iridium (Ir), which is rare on planet Earth and thus suggests an extraterrestrial origin through an impact of a large asteroid. This impact would have ejected enormous quantities of particles and aerosols, shading the solar illumination as attested to by the elimination of the marine photosynthesizing plankton. Such a dark period must have affected life on land. The apparent cold-blooded non-avian dinosaurs, which were used to living in open terrains to absorb the solar illumination, became inactive during the dark period and were incapable of withstanding predators. This was in contrast to cold-blooded crocodilians, turtles and lizards that could hide in refuge sites on land and in the water. Dinosaur relics discovered in Cretaceous Polar Regions were attributed to perennial residents, surviving the nearly half-year-long dark winter despite their ability to leave. The polar concentrations of disarticulated dinosaur bones were suggested as having resulted from a catastrophic burial of a population by floods. However, this should have fossilized complete skeletons. Alternatively, herds of dinosaurs living in high latitudes might have been sexually driven to spend the half year of continuously illuminated polar summer for mating rather than for nourishment, in which the lower latitudes provided as well. The aggressive mating competitions would have left victims among the rivals and of young ones incidentally trampled over, all being consumed and their skeletons disarticulated. Accordingly, the alleged ‘polar dinosaurs’ do not challenge the logical conclusion that the non-avian dinosaurs were cold-blooded, as a result of which they became inactive and subjected to predation during the end-Cretaceous dark period.

Combined effects of increased UV-B and temperature on the pigment-determined marine phytoplankton community of the St. Lawrence Estuary

The combined effects of increased UV-B and temperature on natural marine phyto- plankton from the St. Lawrence Estuary (Canada) were examined in an 8 d mesocosm experiment carried out in Rimouski (Quebec, Canada) in August 2008. We tested the hypothesis that in - creased temperature (+ 3°C) will offset algal growth suppression by UV-B (78% UV-B increase) using duplicate mesocosm experiments containing natural phytoplankton assemblages. The re - sponse of the entire phytoplankton community, in terms of HPLC pigment-based phytoplankton bio mass, community composition (CHEMTAX), xanthophyll cycles photoprotection and quantum yield of photosystem II (the ratio of variable to maximum fluorescence: Fv/Fm), showed a signifi- cant influence of temperature (negative on small phytoplanktonic cells, < 5 µm, and positive on larger diatoms) but only after the peak of the diatom bloom, when nutrients became limited. Inter- actions between temperature and UV-B treatments were significant only for small cells during post-bloom; UV-B induced an increase in phytoplankton biomass at the normal temperature but had no effect at warmer temperatures. Enhancing UV-B delayed the bloom slightly under the nor- mal temperature and spread it over a longer period of time, with no sign of major cellular damage. Our re sults do not support the tested hypothesis, and they suggest that temperature plays a greater role than UV-B radiation in structuring phytoplankton communities, possibly favouring diatoms rather than small cells in a warmer climate scenario. Other effects such as grazing or coastal eutrophication should be considered in future studies.

The determination of heme b in marine phyto- and bacterioplankton

A method for the quantification of heme b in marine phyto- and bacterioplankton is described. Heme b was extracted from filtered cells using a solution of 2.5% octyl β-glucopyranoside in 0.02 M ammonium hydroxide. The extract was analysed by high performance liquid chromatography diode array spectrophotometry. Maximum absorbance for heme b was at 400 nm. Heme b was separated from other pigments using a polystyrene divinyl benzene stationary phase and a gradient elution programme with 0.1% (v:v) nonafluoropentanoic acid in water and 50:50 (v:v) isopropanol:acetonitrile as the mobile phases. Heme b was quantified using Fe (III) protoporphyrin IX chloride (hemin) standards. The detection limit, calculated from 3 × s.d. of the lowest standard was 0.08 pmol or 1.57 nM with a 50 μL injection volume. The first data for heme b in marine phyto- and bacterioplankton are reported. Heme b contents are reported for the eukaryotes Thalassiosira weissflogii, Thalassiosira oceanica, Dunaliella tertiolecta and Emiliania huxleyi, and the prokaryotes Synechococcus WH8102, WH7803, RCC307, Erythrobacter litoralis, Roseobacter denitrificans and Vibrio natriegens. For T. weissflogii, T. oceanica, D. tertiolecta and E. huxleyi cellular heme b concentrations varied between 12 and 60 μmol L − 1 and chlorophyll a to heme b ratios varied between 216 and 309.

Relationships between cell-specific growth rate, and uptake rate of cadmium and zinc by a coastal diatom

Despite the fact that the influence of metal chemistry on metal uptake in marine phyto- plankton has been well studied, the effects of physiological processes such as cellular growth remain less well known. In this study, the cell-specific growth rate of the coastal diatom Thalassiosira pseudonana (Clone-3H) was modified by 3 environmental factors: temperature, irradiance, and the light-dark (LD) cycle. Uptake of Cd and Zn was subsequently quantified using short-term exposure. These environmental factors significantly affected metal uptake. Cd and Zn uptake rates increased with increasing irradiance, temperature, and illumination period. We demonstrate that the metal uptake rate initially increased in proportion with an increase in cell-specific growth rate, and then remained constant. Uptake of Cd and Zn by the diatoms was not affected by 2 photosynthetic inhibitors, suggesting that their uptake was not affected by the photosynthetic activity. There was no obvious diel trend for metal uptake. Thus in this study, cell size, photosynthetic activity, and cell cycle were unlikely to have accounted for the variations in metal uptake at different temperatures, irradi- ances, and LD cycles. The dependence of metal uptake on cell-specific growth rate may have impor- tant implications for the prediction of metal accumulation by marine phytoplankton in different ecosystems or during phytoplankton blooms. Further studies are needed to examine the underlying mechanisms for such relationships at cellular and subcellular levels.

Improvement of marine environmental pollution using eco-system: decomposition and recovery of endocrine disrupting chemicals by marine phyto- and zooplanktons

The decomposition and the recovery of endocrine disrupting chemicals (EDCs) using marine phytoplankton were demonstrated as one of the possible bioremediation methods. Bis(2-ethylhexyl)phthalate and bisphenol A tended to gradually accumulate into the plankton cells during incubation. Furthermore, the recovery of bisphenol A from the synthetic seawater was achieved using a marine pollutant collecting model (eco-system) that combined phyto- and zooplanktons.

Effect of high pH on the growth and survival of marine phytoplankton: implications for species succession

Ten years of pH measurements (1990 to 1999) in the surface waters of the eutrophic Mariager Fjord, Denmark, revealed profound seasonal variation. Typically, pH was relatively constant around 8 from January to March, increased during spring, reached maximum levels in July to August (9 to 9.7), and declined during autumn to about 8 in Octo- ber. The influence of pH on the growth rate of phytoplankton was tested on 3 species (Cer- atium lineatum, Heterocapsa triquetra and Prorocentrum minimum) in laboratory experi- ments. The growth rate was highest at pH 7.5 to 8.0 in all species. The growth rate of C. lineatum declined by ~20% at pH 8.3 to 8.5, while a similar reduction in the growth rate in H. triquetra and P. minimum was observed at pH 8.8 to 8.9. C. lineatum stopped growing above pH 8.8, while growth ceased at about pH 9.45 in H. triquetra and 9.6 in P. minimum. Compilation of literature data on pH and phytoplankton growth suggested that while some species cannot grow at pH 8.4, others are able to grow up to pH 10. However, none of the species studied can attain their maximum growth rate above pH 9. Competition experi- ments using a mixture of C. lineatum, H. triquetra and P. minimum always resulted in the species with the highest pH tolerance (P. minimum) outcompeting the other species, irre- spective of the initial pH value. The role of high pH in the succession of marine phyto- plankton in nature is discussed.

Cadmium uptake and trophic transfer in coastal plankton under contrasting nitrogen regimes

Biological processes (uptake, trophic transfer, regeneration/excretion, and decomposition) are critical in controlling the fate of bioactive metals in the ocean. Whether nutrient conditions can affect metal uptake in marine phyto- plankton and its subsequent trophic transfer along planktonic food chains is little known. We demonstrate that Cd accumu- lation in marine diatoms is dependent on ambient nitrogen conditions and thus the physiological status of phytoplankton cells. Diatom cells Thalassiosira pseudonana and T. weiss- flogii inoculated under nitrogen-limited conditions accumu- lated considerably less Cd than cells maintained under nitro- gen-enriched conditions. The intracellular partitioning of Cd in the diatoms was also positively related to the level of ambi- ent N. Phosphate and silicate starvation did not affect Cd uptake in diatoms. The trophic transfer, quantified by mea- surement of the Cd assimilation efficiency (AE) from ingested diatoms in copepods Calanus sinicus, increased with an increase in the N quota of the diatom cells maintained in a semi-continuous culture. AEs were however comparable in copepods feeding on N-starved and N-enriched diatoms. There was a linear relationship between the Cd AE and the Cd distribution in the cytoplasm of diatoms. The Cd regener- ation rate in copepods was independent of the N status of ingested diatoms. Our study suggests that the cycling of Cd in marine planktonic food chains may be depressed under nitrogen-limited conditions. Conversely, nitrogen enrichment leads to an increase in Cd uptake in phytoplankton cells and zooplankton, elevating the potential exposure of plankton to toxic metals. Thus, nitrogen-stimulated eutrophication may not only affect the cycling of carbon, nitrogen and phosphorus in aquatic ecosystems, but can also result in changes in the cycling of toxic metals in marine food webs.

Stable carbon isotopes in the dissolved organic matter of the sea.

THERE have been several recent investigations concerned with 13C/12C ratios in marine phyto and zooplankters, with metabolic fractionation of these isotopes in laboratory phytoplankton cultures, and with the carbon isotopic composition of the biochemical constituents of oceanic plankton1–5. As far as I know, this is the first report on determinations of the 13C/12C ratios in the dissolved organic matter in the sea.