Marine Cryptophyte Research Articles

Genus Proteomonas is not monotypic: P. agilis sp. nov. (Cryptophyceae, Geminigeraceae) from the Black Sea and hidden diversity of Proteomonas species

Abstract The cryptophytes of the Black Sea are a poorly studied group that has yet to be fully resolved using comprehensive taxonomic approaches, including electron microscopy and molecular genetics. This study describes Proteomonas agilis sp. nov. belonging to a marine cryptophyte genus formerly thought to be monotypic. The morphological characters of the new species align with those currently used to delineate the genus Proteomonas, and are similar to those of the haplomorph P. sulcata, the type species, with minor morphological and molecular modifications. Phylogenetic relationships inferred from nuclear-encoded SSU, LSU, and ITS2 rDNA datasets confirmed that the new species belongs to the monophyletic genus Proteomonas, which is divided into two unequal branches. The largest and relatively long branch contains 18 strains, including P. agilis sp. nov. Comparison of ITS2 rRNA secondary structures using the compensatory base changes approach confirmed the distinction of P. agilis sp. nov. from the other Proteomonas strains. Our findings revealed that the cryptophyte genus Proteomonas is not monotypic but includes a range of unstudied species besides the type species P. sulcata and P. agilis sp. nov. described in this study. Therefore, an integrated approach is required for a careful revision of the genus.

Enhanced biodegradation of para-xylene by the marine cryptophyte Rhodomonas sp. JZB-2 by changing the concentrations of nutrients, iron, and vitamins

Enhanced biodegradation of para-xylene by the marine cryptophyte Rhodomonas sp. JZB-2 by changing the concentrations of nutrients, iron, and vitamins

Preference of Proteomonas sulcata anion channelrhodopsin for NO3\u2212 revealed using a pH electrode method

Ion channel proteins are physiologically important molecules in living organisms. Their molecular functions have been investigated using electrophysiological methods, which enable quantitative, precise and advanced measurements and thus require complex instruments and experienced operators. For simpler and easier measurements, we measured the anion transport activity of light-gated anion channelrhodopsins (ACRs) using a pH electrode method, which has already been established for ion pump rhodopsins. Using that method, we successfully measured the anion transport activity and its dependence on the wavelength of light, i.e. its action spectra, and on the anion species, i.e. its selectivity or preference, of several ACRs expressed in yeast cells. In addition, we identified the strong anion transport activity and the preference for NO3− of an ACR from a marine cryptophyte algae Proteomonas sulcata, named PsuACR_353. Such a preference was discovered for the first time in microbial pump- or channel-type rhodopsins. Nitrate is one of the most stable forms of nitrogen and is used as a nitrogen source by most organisms including plants. Therefore, PsuACR_353 may play a role in NO3− transport and might take part in NO3−-related cellular functions in nature. Measurements of a mutant protein revealed that a Thr residue in the 3rd transmembrane helix, which corresponds to Cys102 in GtACR1, contributed to the preference for NO3−. These findings will be helpful to understand the mechanisms of anion transport, selectivity and preference of PsuACR_353.

Photopigment, Absorption, and Growth Responses of Marine Cryptophytes to Varying Spectral Irradiance.

The underwater light field of lakes, estuaries, and oceans may vary greatly in spectral composition. Phytoplankton in these environments must contain pigments that absorb the available colors of light. If spectral quality changes, acclimation to the new spectral environment would confer an ecological advantage in terms of photosynthesis and growth. Here, we explored the capacity of eight marine cryptophytes to adjust pigmentation in response to changes in spectral irradiance and related effects on light absorption, photosynthetically useable radiation (PUR), and growth rate. The pigment composition of all species changed in some way in response to shifts in spectral irradiance, but not all pigment changes could be considered advantageous in the context of chromatic acclimation. For most species, absorption by chl-a and chl-c2 resulted in highest absorption in the blue region, highest PUR values for blue-light grown cells, and highest growth rates in blue light. The exception was Chroomonas mesostigmatica (CCMP 1168), which contains a high percentage of Cryptophyte-Phycocyanin (Cr-PC) 645, absorbs strongly in the orange-to-red region of the spectrum, and grew fastest under red light. The position and magnitude of the maximum and secondary absorption peak of Cr-PC 569, the phycobiliprotein pigment of Hemiselmis cryptochromatica, varied with spectral irradiance. The underlying cause remains unknown, but may represent a mechanism by which cryptophytes optimize photon capture.

Enriching Rotifers with "Premium" Microalgae: Rhodomonas lens.

The nutritional value of the marine cryptophyte Rhodomonas lens for the filter feeder Brachionus plicatilis as well as its biotechnological potential as a source of phycoerythrin (PE) and polyunsaturated fatty acids (PUFA) were evaluated in semi-continuous cultures maintained with different daily renewal rates (RR), from 10% (R10) to 50% (R50) of the total volume. Steady-state cell density decreased from 22 to 7 × 106cellsmL-1 with increasing RR, with the maximum cell productivity, nearly 0.4gL-1day-1, observed with R40. PE cell content attained the highest values with the highest RR (circa 9pgcell-1). All treatments of R. lens maintained under nitrate-saturated conditions (R20-R50) showed a similar high content of PUFAs, > 60% of total fatty acids (FA), with linolenic acid (18:3n-3) and 18:4n-3, representing 12 and 29% of total FA respectively. The PUFA level in the nitrogen-limited R10 cultures was significantly lower (37%). R. lens promoted higher weight gain in the rotifer B. plicatilis than Tisochrysis lutea (T-ISO), a species commonly used for rotifer culture and enrichment. Significant differences were found in the protein content and in the ratio n-3/n-6 fatty acids among rotifers fed with R. lens from different RRs, with higher values being found in those fed with R. lens from higher RRs. The enrichment of the rotifers for short periods of 3h was sufficient to modify the biochemical composition of the rotifers, but it was evidenced as too short for the accumulation of PUFAs, when compared to long-term (24h) enrichment. The rotifers reflected the higher protein and PUFA content of R. lens cultivated with nutrient sufficient microalgae (R40) after only 3h of enrichment. These results demonstrate that semi-continuous culture of R. lens under appropriate conditions can strongly enhance the nutritional value of this species, being reflected in the growth and biochemical composition of the filter feeder, even in short exposure periods.

Direct and indirect effects of elevated CO2 are revealed through shifts in phytoplankton, copepod development, and fatty acid accumulation.

Change in the nutritional quality of phytoplankton is a key mechanism through which ocean acidification can affect the function of marine ecosystems. Copepods play an important role transferring energy from phytoplankton to higher trophic levels, including fatty acids (FA)—essential macronutrients synthesized by primary producers that can limit zooplankton and fisheries production. We investigated the direct effects of pCO2 on phytoplankton and copepods in the laboratory, as well as the trophic transfer of effects of pCO2 on food quality. The marine cryptophyte Rhodomonas salina was cultured at 400, 800, and 1200 μatm pCO2 and fed to adult Acartia hudsonica acclimated to the same pCO2 levels. We examined changes in phytoplankton growth rate, cell size, carbon content, and FA content, and copepod FA content, grazing, respiration, egg production, hatching, and naupliar development. This single-factor experiment was repeated at 12°C and at 17°C. At 17°C, the FA content of R. salina responded non-linearly to elevated pCO2 with the greatest FA content at intermediate levels, which was mirrored in A. hudsonica; however, differences in ingestion rate indicate that copepods accumulated FA less efficiently at elevated pCO2. A. hudsonica nauplii developed faster at elevated pCO2 at 12°C in the absence of strong food quality effects, but not at 17°C when food quality varied among treatments. Our results demonstrate that changes to the nutritional quality of phytoplankton are not directly translated to their grazers, and that studies that include trophic links are key to unraveling how ocean acidification will drive changes in marine food webs.

Single-Cell and Bulk Fluorescence Excitation Signatures of Seven Phytoplankton Species During Nitrogen Depletion and Resupply.

Phytoplankton play a vital role as primary producers in aquatic ecosystems. One common approach to classifying phytoplankton is fluorescence excitation spectroscopy, which leverages the variation in types and concentrations of pigments among different phytoplankton taxonomic groups. Here, we used a fluorescence imaging photometer to measure excitation ratios ("signatures") of single cells and bulk cultures of seven differently pigmented phytoplankton species as they progressed from nitrogen N-replete to N-depleted conditions. Our objective was to determine whether N depletion alters the fluorescence excitation signature of each species and, if so, how quickly they recover when N (as nitrate) was resupplied, because these factors affect our ability to classify the species correctly. Of the seven species studied, only Proteomonas sulcata, a marine cryptophyte, showed measurable changes in single-cell fluorescence excitation ratios and bulk fluorescence excitation spectra. These changes were likely due to decreases in the cellular concentration of phycoerythrin, a N-rich pigment, as N became scarce. Within 3 h of resupply of N, fluorescence signatures began returning to pre-depletion values and were indistinguishable from N-replete cells by 80 h after resupply. These data suggest that our classification approach is robust for non-PE containing phytoplankton. PE-containing phytoplankton might exhibit systematic changes in their signatures depending on their level of N depletion, but this could be detected and the phytoplankton re-classified following a few hours of incubation in N replete conditions.

Marine Cryptophytes Are Great Sources of EPA and DHA.

Microalgae have the ability to synthetize many compounds, some of which have been recognized as a source of functional ingredients for nutraceuticals with positive health effects. One well-known example is the long-chain polyunsaturated fatty acids (PUFAs), which are essential for human nutrition. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the two most important long-chain omega-3 (ω-3) PUFAs involved in human physiology, and both industries are almost exclusively based on microalgae. In addition, algae produce phytosterols that reduce serum cholesterol. Here we determined the growth rates, biomass yields, PUFA and sterol content, and daily gain of eight strains of marine cryptophytes. The maximal growth rates of the cryptophytes varied between 0.34–0.70 divisions day−1, which is relatively good in relation to previously screened algal taxa. The studied cryptophytes were extremely rich in ω-3 PUFAs, especially in EPA and DHA (range 5.8–12.5 and 0.8–6.1 µg mg dry weight−1, respectively), but their sterol concentrations were low. Among the studied strains, Storeatula major was superior in PUFA production, and it also produces all PUFAs, i.e., α-linolenic acid (ALA), stearidonic acid (SDA), EPA, and DHA, which is rare in phytoplankton in general. We conclude that marine cryptophytes are a good alternative for the ecologically sustainable and profitable production of health-promoting lipids.

Mixotrophy in the marine red-tide cryptophyte Teleaulax amphioxeia and ingestion and grazing impact of cryptophytes on natural populations of bacteria in Korean coastal waters

Cryptophytes are ubiquitous and one of the major phototrophic components in marine plankton communities. They often cause red tides in the waters of many countries. Understanding the bloom dynamics of cryptophytes is, therefore, of great importance. A critical step in this understanding is unveiling their trophic modes. Prior to this study, several freshwater cryptophyte species and marine Cryptomonas sp. and Geminifera cryophila were revealed to be mixotrophic. The trophic mode of the common marine cryptophyte species, Teleaulax amphioxeia has not been investigated yet. Thus, to explore the mixotrophic ability of T. amphioxeia by assessing the types of prey species that this species is able to feed on, the protoplasms of T. amphioxeia cells were carefully examined under an epifluorescence microscope and a transmission electron microscope after adding each of the diverse prey species. Furthermore, T. amphioxeia ingestion rates heterotrophic bacteria and the cyanobacterium Synechococcus sp. were measured as a function of prey concentration. Moreover, the feeding of natural populations of cryptophytes on natural populations of heterotrophic bacteria was assessed in Masan Bay in April 2006. This study reported for the first time, to our knowledge, that T. amphioxeia is a mixotrophic species. Among the prey organisms offered, T. amphioxeia fed only on heterotrophic bacteria and Synechococcus sp. The ingestion rates of T. amphioxeia on heterotrophic bacteria or Synechococcus sp. rapidly increased with increasing prey concentrations up to 8.6×106 cells ml−1, but slowly at higher prey concentrations. The maximum ingestion rates of T. amphioxeia on heterotrophic bacteria and Synechococcus sp. reached 0.7 and 0.3 cells predator−1 h−1, respectively. During the field experiments, the ingestion rates and grazing coefficients of cryptophytes on natural populations of heterotrophic bacteria were 0.3–8.3 cells predator−1h−1 and 0.012–0.033d−1, respectively. Marine cryptophytes, including T. amphioxeia, are known to be favorite prey species for many mixotrophic and heterotrophic dinoflagellates and ciliates. Cryptophytes, therefore, likely play important roles in marine food webs and may exert a considerable potential grazing impact on the populations of marine bacteria.

Osmotolerance in the Cryptophyceae: Jacks-of-all-trades in the Chroomonas Clade

No detailed studies have been performed to date on osmotolerance in cryptophytes, although one species, Chroomonas africana, had previously been reported to grow in freshwater as well as seawater. This study focused on osmotolerance in Chroomonas. Growth at different osmolalities and parameters of contractile vacuole function were examined and compared across a high-resolution phylogeny. Two evolutionary lineages in the Chroomonas clade proved to be euryhaline. Ranges of osmotolerance depended not only on osmolality, but also on culture medium. All cryptophytes contained contractile vacuoles. In the euryhaline strain CCAP 978/08 contractile vacuoles could be observed even at an osmolality beyond that of seawater. In addition the cells accumulated floridoside, an osmoprotectant likely originating from the red algal carbohydrate metabolism of the complex rhodoplast. Further evidence for functional contractile vacuoles also in marine cryptophytes was provided by identification of contractile vacuole-specific genes in the genome of Guillardia theta.

Acquired phototrophy in Mesodinium and Dinophysis – A review of cellular organization, prey selectivity, nutrient uptake and bioenergetics

Acquired phototrophy, i.e. the use of chloroplasts from ingested prey, can be found among some species of dinoflagellates and ciliates. The best studied examples of this phenomenon in these groups are within the ciliate genus Mesodinium and the dinoflagellate genus Dinophysis, both ecologically important genera with a worldwide distribution. Mesodinium species differ considerably in their carbon metabolism. Some species rely almost exclusively on food uptake, while other species rely mostly on photosynthesis. In Mesodinium with acquired phototrophy, a number of prey organelles in addition to chloroplasts may be retained, and the host ciliate has considerable control over the acquired chloroplasts; Mesodinium rubrum is capable of dividing its acquired chloroplasts and can also photoacclimate. In Dinophysis spp., the contents of ciliate prey are sucked out, but only the chloroplasts are retained from the ingested prey. Some chloroplast house-keeping genes have been found in the nucleus of Dinophysis and some preliminary evidence suggests that Dinophysis may be capable for photoacclimation. Both genera have been claimed to take up inorganic nutrients, including NO3−, indicating that processes beyond photosynthesis have been acquired. M. rubrum seems to depend upon prey species within the Teleaulax/Plagioselmis/Geminigera clade of marine cryptophytes. Up until now, Dinophysis species have only been maintained cultured on M. rubrum as food, but other ciliates may also be ingested. Dinophysis spp. and M. rubrum are obligate mixotrophs, depending upon both prey and light for sustained growth. However, while M. rubrum only needs to ingest 1–2% of its carbon demand per day to attain maximum growth, Dinophysis spp. need to obtain about half of their carbon demand from ingestion for maximum growth. Both Mesodinium and Dinophysis spp. can survive for months in the light without food. The potential role for modeling in exploring the complex balance of phototrophy and phago-heterotrophy, and its ecological implications for the mixotroph and their prey, is discussed.

Electronic coherence lineshapes reveal hidden excitonic correlations in photosynthetic light harvesting

The effective absorption cross-section of a molecule (acceptor) can be greatly increased by associating it with a cluster of molecules that absorb light and transfer the excitation energy to the acceptor molecule. The basic mechanism of such light harvesting by Förster resonance energy transfer (FRET) is well established, but recent experiments have revealed a new feature whereby excitation is coherently shared among donor and acceptor molecules during FRET. In the present study, two-dimensional electronic spectroscopy was used to examine energy transfer at ambient temperature in a naturally occurring light-harvesting protein (PE545 of the marine cryptophyte alga Rhodomonas sp. strain CS24). Quantum beating was observed across a range of excitation frequencies. The shapes of those features in the two-dimensional spectra were examined. Through simulations, we show that two-dimensional electronic spectroscopy provides a probe of the adiabaticity of the free energy landscape underlying light harvesting.

Coherently wired light-harvesting in photosynthetic marine algae at ambient temperature

Photosynthesis makes use of sunlight to convert carbon dioxide into useful biomass and is vital for life on Earth. Crucial components for the photosynthetic process are antenna proteins, which absorb light and transmit the resultant excitation energy between molecules to a reaction centre. The efficiency of these electronic energy transfers has inspired much work on antenna proteins isolated from photosynthetic organisms to uncover the basic mechanisms at play. Intriguingly, recent work has documented that light-absorbing molecules in some photosynthetic proteins capture and transfer energy according to quantum-mechanical probability laws instead of classical laws at temperatures up to 180 K. This contrasts with the long-held view that long-range quantum coherence between molecules cannot be sustained in complex biological systems, even at low temperatures. Here we present two-dimensional photon echo spectroscopy measurements on two evolutionarily related light-harvesting proteins isolated from marine cryptophyte algae, which reveal exceptionally long-lasting excitation oscillations with distinct correlations and anti-correlations even at ambient temperature. These observations provide compelling evidence for quantum-coherent sharing of electronic excitation across the 5-nm-wide proteins under biologically relevant conditions, suggesting that distant molecules within the photosynthetic proteins are 'wired' together by quantum coherence for more efficient light-harvesting in cryptophyte marine algae.

Effects of nitrogen starvation on the photosynthetic physiology of a tropical marine microalga Rhodomonas sp. (Cryptophyceae)

The effects of nitrogen starvation on biomass composition and photosynthetic function were examined in the marine cryptophyte Rhodomonas sp. Batch-cultured cells in N-sufficient medium showed a 2.5-fold increase in total carbohydrate content, and a 33% increase in cell volume when the cultures reached the stationary growth phase. These cultures also increased the ratio of phycoerythrin (PE)/hydrosoluble proteins from 6 to 22% by the 4th and 10th day of culture, respectively. In contrast, light-saturated photosynthetic activity ( P m) progressively decreased, and the value obtained at the beginning of the stationary phase was about 45% of that obtained for cells in the late exponential growth phase. Transfer to N-lacking medium caused a 3.2-fold increase in cell volume. N starvation also triggered a rapid decline in N-containing compounds such as hydrosoluble proteins and photosynthetic pigments, causing an almost complete loss of PE. The ratio of PE/hydrosoluble proteins decreased from 6 to 1% after 6 d of N deprivation. Furthermore, the PSII fluorescence capacity declined under N-starved conditions, which caused a pronounced decrease in both the P m (circa 90%) and the apparent photosynthetic efficiency (circa 55%). Under these conditions, photosynthetically fixed carbon was used to synthesize large amounts of carbohydrates. We suggest that, in addition to the role of phycoerythrin as a light-harvesting pigment, Rhodomonas sp. responds to N-depleted conditions by mobilizing combined nitrogen from biliproteins.

Evidence of monomeric photosystem I complexes and phosphorylation of chlorophyll a/c-binding polypeptides in Chroomonas sp. strain LT (Cryptophyceae).

Thylakoid membranes of the cryptophyte Chroomonas sp. strain LT were solubilized with dodecyl-beta-maltoside and subjected to sucrose density gradient centrifugation. The four pigment protein complexes obtained were subsequently characterized by absorption and fluorescence spectroscopy, SDS-PAGE, and Western immunoblotting using antisera against the chlorophyll a/c-binding proteins of the marine cryptophyte Cryptomonas maculata and the reaction-center protein D2 of photosystem II of maize. Band 1 consisted mainly of free pigments, phycobiliproteins, and chlorophyll-a/c-binding proteins. Band 2 represented a major chlorophyll a/c-binding protein fraction. A mixture of photosystem II and photosystem I proteins comprised band 3, whereas band 4 was enriched in proteins of photosystem I. Western immunoblotting demonstrated the presence of chlorophyll a/c-binding proteins and their association with photosystem I in band 4. Phosphorylation experiments showed that chlorophyll a/c-binding proteins became phosphorylated. Negative staining electron microscopy of band B4 revealed photosystem I particles with dimensions of 22 nm. Our work showed that PSI-LHCI complexes of cryptophytes are similar to those of Chlamydomonas rheinhardtii, the diatom Phaeodactylum tricornutum, and higher plants.

Rhodopsin-Mediated Photoreception in Cryptophyte Flagellates

We show that phototaxis in cryptophytes is likely mediated by a two-rhodopsin-based photosensory mechanism similar to that recently demonstrated in the green alga Chlamydomonas reinhardtii, and for the first time, to our knowledge, report spectroscopic and charge movement properties of cryptophyte algal rhodopsins. The marine cryptophyte Guillardia theta exhibits positive phototaxis with maximum sensitivity at 450 nm and a secondary band above 500 nm. Variability of the relative sensitivities at these wavelengths and light-dependent inhibition of phototaxis in both bands by hydroxylamine suggest the involvement of two rhodopsin photoreceptors. In the related freshwater cryptophyte Cryptomonas sp. two photoreceptor currents similar to those mediated by the two sensory rhodopsins in green algae were recorded. Two cDNA sequences from G. theta and one from Cryptomonas encoding proteins homologous to type 1 opsins were identified. The photochemical reaction cycle of one Escherichia-coli-expressed rhodopsin from G. theta ( GtR1) involves K-, M-, and O-like intermediates with relatively slow (∼80 ms) turnover time. GtR1 shows lack of light-driven proton pumping activity in E. coli cells, although carboxylated residues are at the positions of the Schiff base proton acceptor and donor as in proton pumping rhodopsins. The absorption spectrum, corresponding to the long-wavelength band of phototaxis sensitivity, makes this pigment a candidate for one of the G. theta sensory rhodopsins. A second rhodopsin from G. theta ( GtR2) and the one from Cryptomonas have noncarboxylated residues at the donor position as in known sensory rhodopsins.

Fe-responsive accumulation of redox proteins ferredoxin and flavodoxin in a marine cryptomonad

Fe deficiency has been documented in diverse marine environments ranging from pelagic high-nutrient, low chlorophyll (HNLC) regions to coastal systems. Detection of specific Fe-responsive proteins in phytoplankton has provided a sensitive approach to assessing Fe deficiency in natural waters. Here, we report on the development and applicability of taxon-specific polyclonal antisera to monitor the accumulation of two such Fe-responsive proteins, flavodoxin and ferredoxin (Fd) in cryptomonad algae. Reactivity of these immunoreagents was limited primarily to cryptomonads. Anti-Fd cross-reacted with a broad spectrum of both marine and freshwater cryptophytes whereas anti-flavodoxin recognized only flavodoxin from Rhodomonas lens. Assessment of Fd and flavodoxin accumulation in R. lens grown under various levels of Fe demonstrated an apparent uncoupling of flavodoxin expression from physiological Fe deficiency in this species. It appears that flavodoxin accumulates in response to external Fe availability as supported by results of a chelator addition experiment which demonstrated rapid accumulation of flavodoxin in Fe-replete cells of R. lens without concomitant physiological deficit following addition of the fungal siderophore desferrioxamine B.

Chemoreception in a marine cryptophyte: Behavioral plasticity in response to amino acids and nitrate

The behavioral responses of Chroomonas sp. to ammonium, nitrate, and 19 individual amino acids were examined by computer-assisted video motion analysis. Cells were cultured with either glycine or nitrate as the sole nitrogen source. Relative to seawater, rates at which glycine-grown cells stopped and turned were significantly reduced in response to 10−6 and 10−7 M glutamate, methionine, alanine, and aspartate. This response was akin to the tumbling behavior (chemotaxis) displayed by flagellated bacteria. When cultured in nitrate, Chroomonas sp. did not react to amino acids and ammonium but did significantly reduce stopping and turning in response to 10−6 M nitrate. These results are the first to demonstrate chemoreception in any cryptophyte species. Because Chroomonas sp. commonly lives in habitats where light and inorganic nutrients are limiting, behavioral mechanisms that maximize use of both amino acids and nitrate would seem particularly adaptive.

Late summer phytoplankton species composition and biomasses in the Eastern Gulf of Finland

Abstract The nutrient load of the River Neva and the St. Petersburg region strongly affects the trophic status of the eastern Gulf of Finland. The extent of eutrophication and its effect on the phytoplankton community were studied in the eastern Gulf of Finland in August 1990–1992. The phytoplankton of the easternmost part was dominated by an assemblage of fresh-water and brackish-water species, including numerous indicators of eutrophication. Inside the St. Petersburg flood-protection barrier, phytoplankton growth was limited, probably mainly by turbidity; and it consisted essentially of fresh-water cryptophytes. In 1990 and 1992, marine cryptophytes dominated in the open Gulf. The highest phytoplankton biomasses occurred in the estuary outside the barrier, where polluted river water with a high N/P-ratio mixes with brackish deep water with a low N/P-ratio. The phytoplankton community in the Neva estuary was dominated by the blue-green alga Planktothrix agardhii. In 1991, strong outflow of river water pushed the bloom of Planktothrix agardhii exceptionally far westwards. In addition to the heavy loading, meteorological and hydrographical factors strongly influence the distribution of blue-green algal blooms in the eastern Gulf of Finland.

EFFECTS OF LIGHT AND GLYCEROL ON THE ORGANIZATION OF THE PHOTOSYNTHETIC APPARATUS IN THE FACULTATIVE HETEROTROPHPYRENOMONAS SALINA(CRYPTOPHYCEAE)1

ABSTRACTThe marine cryptophytePyrenomonas salinaSantore is capable of autotrophic and heterotrophic nutrition. We studied the physiological and ultrastructural changes that accompany the shift between these nutritional modes. The addition of glycerol to batch cultures ofP. salina,grown at an irradiance limiting for photoautotrophic growth, increased its growth rate and induced specific biochemical and structural changes in its photosynthetic system. Results from extracted pigment analyses, thin‐section electron microscopy, and freeze‐fracture electron microscopy indicated that glycerol addition reduced the cell phycoerythrin content, phycoerythrin to chlorophyll a ratio, degree of thylakoid packing, number of thylakoids · cell−1, and PSII particle size. These properties were reduced to a similar extent in cells grown photoautotrophically under an irradiance saturating for growth. These results are consistent with the hypothesis that enhancement of heterotrophic potential occurs at the expense of light‐harvesting ability in glycerol‐grownP. salina.