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Background: The freshwater algae and cyanobacteria growth inhibition test (OECD test guideline 201) is frequently used to assess the ecotoxicity of chemicals or particles. A central issue is the measurement of algal growth by quantifying algal biomass over time. Chlorophyll fluorescence measurements are recommended for the testing of particles. The analysis of in vivo fluorescence is the simplest and fastest approach, but is only suitable if there is no interference with the materials. Therefore, in vitro fluorescence analysis is often preferred. We carried out a comprehensive comparison of chlorophyll fluorescence measurements in vitro and in vivo to evaluate the suitability of rapid in vivo testing for the determination of Raphidocelis subcapitata biomass in the presence of diverse particles. Results: For the in vitro measurement, we applied a method that separates particles from chlorophyll using locust bean gum. We tested inorganic and organic particles (including alloys and polymers), ion-releasing and non-releasing materials, and particle sizes in the nanometer to micrometer range with a variety of shapes (spherical, flaky and fibrous). Some of the materials were nontoxic, whereas others showed varying degrees of toxicity (ErC50 = 0.2–100 mg/L in both methods). There were only minor differences between the methods in ErC50 values and the percent inhibition at various test concentrations, but the confidence intervals for the ErC50 values in vivo were narrower and were covered by the range observed in vitro. The in vivo approach showed no limitations, whereas the validity criteria listed in OECD test guideline 201 were not always fulfilled by the in vitro measurements. Conclusion: The in vivo approach was a suitable and time-saving method for a wide range of particles, although we cannot completely exclude the possibility that some particles may interfere with fluorescence measurement. To avoid false assessments, pre-tests with simple measurements are therefore recommended. [ABSTRACT FROM AUTHOR]

Benthic microbial mats in the glacial-fed meltwater streams are hotspots of productivity in the McMurdo Dry Valleys (MDV), Antarctica. Benthic diatoms are common in these mats and the >45 primarily endemic taxa represent the most diverse group of eukaryotes in the MDV. In this harsh polar desert, streams are thermally dynamic with daily water temperatures varying 6-9 °C and daily maximum temperatures as high as 15 °C. Stream temperature may play a role in determining growth rates and survival strategies. To understand taxon-specific adaptations to their environment, we measured the growth rates of unialgal cultures of four diatom taxa ( Psammothidium papilio, Hantzschia abundans, Hantzschia amphioxys, and Hantzschia amphioxys f . muelleri) under three temperature conditions (7.6, 10, and 15 °C) that were representative of maximum daily stream temperatures. We found that P. papilio exhibited a constant growth rate across the full temperature range; this species is most common in streams that begin to flow early in the summer and with less variable thermal regimes. Growth rates for H. abundans were greatest at 15 °C, but showed a non-linear relationship with temperature. H. amphioxys f . muelleri grew faster than the other taxa studied and thrived at 10 °C. Hantzschia amphioxys grew only at the two lower temperatures. These results aligned with the observed relationships between each taxon's relative abundance and stream temperatures in the long-term record maintained by the MDV Long-Term Ecological Research program. Overall, our observations suggest that differences in thermal optima may be one factor contributing to and maintaining the diversity of benthic diatom flora in the MDV. [ABSTRACT FROM AUTHOR]

Floating seaweeds are important dispersal vehicles, especially for organisms with limited movement capacities and for the seaweeds themselves. The persistence of floating seaweeds is determined by the balance between their acclimation potential and the environmental pressures at the sea surface. Solar radiation is the most important inducer of physiological stress, varying in intensity throughout the day and the year. Therefore photoinhibition and subsequent recovery can change depending on the daily radiation dose and season. The bull kelp Durvillaea antarctica is one of the most common floating seaweeds in the southern oceans, including New Zealand, Chile, and most subantarctic islands. Herein, daily cycles of maximum quantum yield ( Fv/ Fm), photoinhibition and recovery levels were examined in microcosm experiments with floating D. antarctica throughout the year, focusing on the blade side exposed to solar radiation (sunny vs shadow side). Also, the effect of simulated wave action (blade turnover) and ultraviolet radiation (UVR) on photoinhibition and recovery of Fv/ Fm was evaluated. Significant differences in maximum quantum yield were observed between blade sides, with lowest values on the sun-exposed side, especially during noontime and spring/summer months. Phlorotannins and pigments were measured during seasons with the most intense solar radiation (late spring, early summer), when Fv/ Fm values were lowest. Phlorotannin, but not pigment concentrations, differed between sunny (lower concentration) and shadow blade sides (higher concentration) and throughout the daily cycle. Both blade sides had similar photoinhibition and recovery levels when blades were constantly turned over. Absence of UVR favoured the recovery capacity of Fv/ Fm in both blade sides, suggesting that the photorecovery potential of floating kelps depends on the environmental conditions that kelp rafts face at the sea surface (e.g. cloudy vs sunny days, intense seawater movement and splashing vs calm sea conditions). The results confirm that photobiological stress is more severe during summer and on continuously sun-exposed blade sides, thereby damaging the blades and suppressing the floating time of D. antarctica. [ABSTRACT FROM AUTHOR]

The authors used 5 species of periphytic algae to conduct toxicity assays of 20 herbicides. The 5 tested species represent riverine primary producers most likely to be affected by herbicides. A fluorescence microplate toxicity assay was used as an efficient and economical high-throughput assay. Toxicity characteristics were analyzed, focusing on their relationship to herbicide mode of action. The relative differences between 50% and 10% effect concentrations depended on herbicide mode of action, rather than tested species. Moreover, a clear relationship between sensitive species and herbicide mode of action was also observed. Green alga was most sensitive to herbicides of 2 mode of action groups: inhibitors of protoporphyrinogen oxidase and very long-chain fatty acid synthesis. Diatoms were most sensitive to herbicides of 1 mode of action group: 4-hydroxyphenyl-pyruvate-dioxygenase inhibitors. Cyanobacterium was most sensitive to herbicides of 1 mode of action group: inhibitors of acetolactate synthase. The species sensitivity distribution based on obtained data was also analyzed. The slopes of the species sensitivity distribution significantly differed among modes of action, suggesting that difference in species sensitivity is specific to the mode of action. In particular, differences in species sensitivity were markedly large for inhibitors of acetolactate synthase, protoporphyrinogen oxidase, and very long-chain fatty acid synthesis. The results clearly showed that a single algal species cannot represent the sensitivity of an algal assemblage. Therefore, multispecies algal toxicity data are essential for substances with specific modes of action. Environ Toxicol Chem 2016;35:368-375. © 2015 SETAC [ABSTRACT FROM AUTHOR]

Four emulsion-filled gelatin gels varying in fat content (5 and 15%) and type of emulsifier (whey protein isolate: fat droplets bound to matrix; Tween 20: fat droplets unbound to matrix) were studied. We investigated (1) the formation and clearance dynamics of fat deposition on the tongue using in vivo fluorescence during oral processing; (2) influence of fat droplet characteristics on fat deposition on tongue and fatty mouthfeel; and (3) effect of follow-up consumption (water or gelatin gel) on the removal of fat deposition on the tongue. We conclude that fat fraction deposited on tongue and fatty perception increased with increasing mastication time, and decreased after expectoration with increasing clearance time. Fat fraction deposited on tongue and fatty perception are higher in gels with unbound droplets compared to bound droplets, as well as in gels with 15% fat compared to 5% fat. Water removed deposited fat from the tongue faster than gelatin gel. [ABSTRACT FROM AUTHOR]

The objective of lung gene therapy is to reach the respiratory epithelial cells in order to deliver a functional nucleic acid sequence. To improve the synthetic carrier's efficacy, knowledge of their biodistribution and elimination pathways, as well as cellular barriers faced, depending on the administration route, is necessary. Indeed, the in vivo fate guides the adaptation of their chemical structure and formulation to increase their transfection capacity while maintaining their tolerance. With this goal, lipidic fluorescent probes were synthesized and formulated with cationic lipophosphoramidate KLN47 (KLN: Karine Le Ny). We found that such formulations present constant compaction properties and similar transfection results without inducing additional cytotoxicity. Next, biodistribution profiles of pegylated and unpegylated lipoplexes were compared after systemic injection in mice. Pegylation of complexes led to a prolonged circulation in the bloodstream, whereas their in vivo bioluminescent expression profiles were similar. Moreover, systemic administration of pegylated lipoplexes resulted in a transient liver toxicity. These results indicate that these new fluorescent compounds could be added into lipoplexes in small amounts without perturbing the transfection capacities of the formulations. Such additional properties allow exploration of the in vivo biodistribution profiles of synthetic carriers as well as the expression intensity of the reporter gene. [ABSTRACT FROM AUTHOR]

Current strategies for early detection of breast and other cancers are limited in part because some lesions identified as potentially malignant do not develop into aggressive tumors. Acid pH has been suggested as a key characteristic of aggressive tumors that might distinguish aggressive lesions from more indolent pathology. We therefore investigated the novel class of molecules, pH low insertion peptides (pHLIPs), as markers of low pH in tumor allografts and of malignant lesions in a mouse model of spontaneous breast cancer, BALB/neu-T. pHLIP Variant 3 (Var3) conjugated with fluorescent Alexa546 was shown to insert into tumor spheroids in a sequence-specific manner. Its signal reflected pH in murine tumors. It was induced by carbonic anhydrase IX (CAIX) overexpression and inhibited by acetazolamide (AZA) administration. By using 31P magnetic resonance spectroscopy (MRS), we demonstrated that pHLIP Var3 was retained in tumors of pH equal to or less than 6.7 but not in tissues of higher pH. In BALB/neu-T mice at different stages of the disease, the fluorescent signal from pHLIP Var3 marked cancerous lesions with a very low false-positive rate. However, only ~60% of the smallest lesions retained a pHLIP Var3 signal, suggesting heterogeneity in pH. Taken together, these results show that pHLIP can identify regions of lower pH, allowing for its development as a theranostic tool for clinical applications. [ABSTRACT FROM AUTHOR]

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During the late austral summer and early autumn 1995 (March-April), an oceanographic cruise was conducted along the Strait of Magellan in order to study the photosynthetic performance of phytoplankton assemblages. The high correlations between the pico-nano fractions and both the total biomass concentrations (Chl a) and primary production rates emphasized the role of these fractions in driving the primary production processes. Repeated P versus E experiments were conducted in the most productive area of the Strait, Paso Ancho, in order to assess the influence of the tidal currents on phytoplankton photosynthetic performance. These data were compared to those available from a previous cruise (February-March, 1991) carried out along the Strait. In the Pacific-Andean sector, the primary production processes were highly controlled by wind, land forcing, and irradiance availability. In the Paso Ancho, the observed highest photosynthetic capacity $$ P_{\text{m}}^{\text{B}} $$ (up to 6.5 mgC mgChl a h) and the high primary production rates may due to the continuous mixing of the water column forced by the strong tidal currents within the photic layer. The non-limiting, macro-nutrient concentrations in the Strait indicate that the available irradiance and the depth of mixed layer are the main driving factors of the primary production processes. The photosynthetic performance of the phytoplankton assemblages renders the Strait a unique ecosystem, which is more similar to those of the mid-latitudes than to those of the periantarctic areas. [ABSTRACT FROM AUTHOR]

The response of Prorocentrum donghaiense and Thalassiosira weissflogii pigments under nitrate (N) and phosphate (P) limitation were studied using HPLC and in vivo fluorescence protocols in batch cultures. For P. donghaiense, the pigment ratio was kept stable under different nutrient conditions from the results of HPLC. For T. weissflogii, there was a lower ratio of chlorophyllide to Chl a during the exponential phase, but the reverse during the stationary phase. Different members of the phytoplankton had different pigments response mechanisms under nutrient limitation. From the results of in vivo fluorescence, the ratio of peridinin to Chl a for P. donghaiense increased in nutrient-free culture, while it was kept stable for nutrient-limited cultures during the exponential phase. For T. weissflogii, the ratio of fucoxanthin to Chl a for each culture increased during the exponential phase, but the ratio under N limitation was apparently lower than that for P limitation during the stationary phase. The results indicate that both pigment ratios from HPLC and in vivo fluorescence of T. weissflogii were changed greatly under different nutrient conditions, which suggests that both ratios could be used as indicators of algal physiological status in different nutrient conditions. (Handling editor: Jin-Zhong Cui) [ABSTRACT FROM AUTHOR]

The effects of nitrate, ammonium and phosphate on the abundance, chlorophyll a content (chl a), in vivo fluorescence, particulate organic carbon, nitrogen, phosphorus and cell morphology of the diatom Skeletonema costatum, the dinoflagellate Prorocentrum micans and the coccolithophore Emiliania huxleyi were investigated in the laboratory. The carbon:chlorophyll a ratio (as weight), a parameter often used in productivity estimates, differed substantially among the three species as well as at different nutrient concentrations at the end of the exponential growth phase. The cell chl a content was higher in the earlier phases of growth in all three species in agreement with previous investigations. Average chl a content per cell during the experiments was higher in P. micans (8 pg) than in S. costatum (0.4 pg) and E. huxleyi (0.2 pg). However, chl a content per unit volume was higher in E. huxleyi (~15 fg μm−3) than in S. costatum (~7 fg μm−3) and P. micans (~1 fg μm−3). Prorocentrum micans cultures reached the highest total biovolume (74 mm3 L−1 and was 3 and 5 times higher than S. costatum and E. huxleyi cultures, respectively) under high nutrient concentrations. Nevertheless, total chl a concentration of S. costatum culture was almost twice higher (122 μg L−1) than that of the other two species at the end of the exponential growth phase. Phosphate consumption by S. costatum occurred at higher rates compared to the other two species during the experimental period, probably showing that this nutrient was more favourable for this species. Our findings from these laboratory experiments emphasize that chl a values in the natural habitat may not accurately indicate actual phytoplankton biomass. [ABSTRACT FROM AUTHOR]

The fluorescence emitted at 710 nm by Phaeodactylum tricornutum (F710) was characterized. Development of F710 was found to be regulated by the quality of light needed for algal growth: weak red light absorbed mainly by Chl a induced its development, and weak blue-green light absorbed mainly by fucoxanthin and Chl c suppressed it. The difference spectra between cells grown under the two light conditions revealed two Chl a forms, absorption peaks of which were located at 692 nm (Chl a692) and at 703 nm (Chl a703), respectively, in red-light-grown cells. During cell growth under red light, the appearance and intensification of the emission correlated well with development of Chl a692 and Chl a703 suggesting that the two forms of Chl a are involved in the energy flow to F710. A clear induction phenomenon characteristic of the PSII fluorescence was observed not only with the emission at 680 nm but also with F710, indicating that F710 is emitted by PSII Chl a. Development of F710 under red light was sensitive to cycloheximide, indicating that the development of the energy flow to F710 requires protein synthesis and that the emitter is installed in a protein encoded in the nuclear genome like the light-harvesting complex (LHC). Centrifugal fractionation of pigment–protein complexes revealed F710 to be located at fractions slightly heavier than the major LHC. Development of F710 was also found in red-light-grown cells of the diatom Nitzschia closterium. [ABSTRACT FROM PUBLISHER]

A laboratory experiment was carried out to estimate the extent of changes in fluorescence characteristics of three oscillatorian strains (Planktothrix mougeotii, P. prolifica, and Tychonema bourrellyi) grown in batch culture at two light intensities (9 and 39 µΕm[sup--2]s[sup--1] ). The following set of measurements was performed in the late log-phase of the growth of the cultures: recording of in vivo fluorescence spectra at 680 nm by excitation in the range 400--660 nm, determination of chlorophyll a and phycobilin concentrations, cells and trichome numbers, mean cellular volume, and dry weight of the culture. In T. bourrellyi and P. prolifica the lower light intensity stimulated the synthesis of phycoerythrin, and as a consequence the fluorescence response. Negligible changes in the pigment composition and shape of spectra of the P. mougeotii strain were observed. Differences in quantitative fluorescence characteristics normalized to phytoplankton biomass equivalents for cyanobacterial cultures grown at two light intensities are presented. [ABSTRACT FROM AUTHOR]

Three methods of algal quantification (direct cell counts, chlorophyll a extraction, in vivo fluorescence) were used to evaluate the response of the unicellular green flagellate Tetraselmis suecica to nutrients and grazers. Nutrient enrichment enhanced total cell counts, chlorophyll a concentration and in vivo and DCMU-fluorescence. Photosynthetic efficiency was reduced in the complete F2 medium as indicated by the high level of in vivo fluorescence, whereas photosynthetic efficiency was increased by the introduction of mussels to the F2 medium. The addition of mussels significantly increased the proportion of non-motile cells, but did not reduce the total cell count. The effect of mussel grazing on algae could be underestimated if only total cells were counted or only the chlorophyll a concentration was measured. The results indicate that these three methods measure different properties of an algal culture and are complementary to each other in assessing the quality and quantity of an algal population. Direct algal counting offers a reliable numerical assessment for cell population abundance. Chlorophyll a concentration was closely correlated to the total cell count. In the presence of mussels, in vivo fluorescence did not correlate with either algal cell counts or chlorophyll a concentration, indicating that the measurement of in vivo fluorescence may be misleading for estimating algal abundance under different culture conditions. [ABSTRACT FROM AUTHOR]

The phylogenetic distribution of photosystem I-associated polypeptides was assessed by immunoblotting algal thylakoid membrane polypeptides with antisera generated against the P700-chlorophyll a protein (CC I) and a photosystem I light-harvesting chlorophyll-protein (LHC Ib). Polypeptide cross-reacting with the CC I apoprotein were found in 20 species representing four classes of unicellular algae. Polypeptides sharing antigenicity with spinach LHC Ib were observed only in algal species containing chlorophyll b. Tetraselmis spp. (Pleurastrophyceae), rich in chlorophyll b (Chl a:b ≤ 1.2), exhibited marked heterogeneity in the composition of their CC I and LHC Ib cross-reactive polypeptides. When immunoblotted with antisera against CC I, all Tetraselmis clones examined exhibited a 25-kD polypeptide in greater abundance than the 58-kD CC I apoprotein characteristic of higher plants and other green algal thylakoids. Three etraselmis clones (RG 6, RG 11, RG 12) exhibited an 81-kD polypeptide with strong antigenecity toward the LHG Ib antisera in contrast to the 24-kD cross-reactive polypeptides found in spinach, green algae, and one Tetraselmis clone (RG 5) Associated with the unique photosystem I polypeptide composition in Tetraselmis spp., Chll:P700 ratios for the group are 2-5 times greater than those observed for higher plants or other green algae. The chlorophyll b enrichment, unusual composition of photosystem I cross-reactive polypeptides, and heterogeneity of these polypeptides within isolates of these Tetraselmis might make this genus useful for investigations of the functional organization of chlorophyll b in light harvesting systems. These features also support the view of an alternative phyletic origin for the Pleurastrophyceae. [ABSTRACT FROM AUTHOR]

The rate of photosynthesis and nitrate uptake are related to the iron concentration in the medium for the green alga Scenedesmus quadrlcauda (Turp.) Breb. Increased iron leads to changes in chlorophyll a concentration, carbon fixation rate per chlorophyll a and in vivo fluorescence characteristits. These parameters all indicate that the efficieny of c is related to iron nutrition. Nitrate uptake rate is also a function of both Fe and light. Iron-limited cultures had decreased nitrate uptake at low light whereas ammonium uptake was relatively constant. Iron-limited cultures fixed about twice as much carbon into protein relative to the total carbon fixed. Iron plays a crucial role in the bioenergetics of carbon and nitrogen metabolism and may be important in controlling patterns of productivity. [ABSTRACT FROM AUTHOR]

Determinations of chlorophyll a and in vivo fluorescence of photosynthetic pigments were used to study vertical and horizontal distribution of phytoplankton in Lake Tanganyika (East Africa). Blue excited fluorescence (IVFb) was an approximate predictor of chlorophyll a at different depths and locations. Green excited fluorescence (IVFg), which reflects phycoerythrin in cyanobacteria, explained chlorophyll a variation equally well, and in combination with IVFb the degree of explanation was improved to 87% (n = 90). Particularly during the shallow stratification in March-May, the maxima of chlorophyll a, IVFb and IVFg were located within the thermocline. Such distribution may have resulted from the high penetration of UV light, often accentuated by very shallow daytime thermal stratification, leading to inhibition of phytoplankton near the surface. Because the decrease of chlorophyll a specific IVFb was less striking towards the surface, the decrease of IVFb was not caused by light inhibition only. In October-November, epilimnetic IVFb and chlorophyll a values seemed tobe consistently higher than in April-May and often showed remarkablepatchiness. The sometimes very dense phytoplankton blooms (Anabaena sp., Cyanobacteria) observed in the central and southern parts of thelake, suggest that local upwelling or mixing events may be importantfor the development of phytoplankton in Lake Tanganyika. [ABSTRACT FROM AUTHOR]