Analysis of concentration-dependent effects of copper and PCB on different Chattonella spp. microalgae (Raphidophyceae) cultivated in artificial seawater medium

In the present study, the effect on the chlorophyll a and the total protein content as well as the Chattonella spp. cell viability were examined after concentration-dependent exposure to CuCl2 and Aroclor 1242. The comparison between various raphidophyte strains provides an insight into the different susceptibilities to contaminants of Chattonella subsalsa (CSNAV-1), C. marina var . marina (CMCV-1) and C. marina var. ovata (COPV-2). The microalgae were cultivated in artificial seawater medium. Exponentially growing microalgae (8-10 days in culture) were used for exposure experiments. We observed in all three raphidophyte species cytotoxicity-mediated modifications beginning at concentrations of 150 and 200μM of the heavy metal copper after 24 hours exposure. But interestingly, the three strains exhibited only slight differences in their susceptibility to CuCl2. C. subsalsa and C. marina var. marina cells were first affected at the chlorophyll a level and in cell viability. The total protein amount was reduced significantly only after exposure to 300μM of CuCl2. However, C. marina var. ovata microalgae showed similar reduction curves for all three analysed cytotoxicity endpoints after heavy metal exposure. On the other hand, after Aroclor 1242 incubation the cytotoxic modification pattern indicated clearly the different susceptibilities of the three raphidophyte strains. C. subsalsa cells noticeably exhibited a decrease in the analysed pigment amount (30-20% compared to that of the control) already after 0.007mg/L PCB exposure. In contrast, cell viability and total protein content were slightly reduced and fell below the 50% threshold after 0.7 and 3.3mg/L of Aroclor 1242, respectively. Interestingly, C. marina var. ovata showed almost no cytotoxic modification caused by the PCB mixture. Only the concentration of 0.7mg/L Aroclor 1242 clearly affected the cell viability. As opposed to that we observed a concentration-dependent decrease of cell viability and chlorophyll a amount in CMCV-1 microalgae. These observations confirmed that the susceptibility of the raphidophytes strains CSNAV-1, CMCV-1 and COPV-2 is contaminant- dependent. We showed differences even between two variants of Chattonella (Chattonella marina var. marina and C. marina var. ovata). Furthermore, we were able to show the different mode of action of two common pollutants by simple cytotoxic parameters like total protein and chlorophyll a content as well as by cell counting analysis

The luminosity function and the rate of Swift's Gamma Ray Bursts

We invert directly the redshift - luminosity distribution of observed long Swift GRBs to obtain their rate and luminosity function. Our best fit rate is described by a broken power law that rises like (1+z)^2.1{+0.5-0.6} for 0<z<3 and decrease like (1+z)^-1.4{+2.4-1.0} for z>3. The local rate is 1.3^{+0.6-0.7} [Gpc^-3 yr^-1]. The luminosity function is well described by a broken power law with a break at L* = 10^52.5{+-0.2}[erg/sec] and with indices alpha = 0.2^{+0.2-0.1} and beta = 1.4^{+0.3-0.6}. The recently detected GRB 090423, with redshift ~8, fits nicely into the model's prediction, verifying that we are allowed to extend our results to high redshifts. While there is a possible agreement with the star formation rate (SFR) for z<3, the high redshift slope is shallower than the steep decline in the SFR for 4<z. However we cannot rule out a GRB rate that follows one of the recent SFR models.Comment: Significantly revised version, including a comparison of the GRB rate to new results on the SFR, revisions in response to the referee comments and comparison with other works on the GRB rate. 28 pages, 14 figures, 5 tables. MNRAS

An Observational Limit on the Earliest GRBs

We predict the redshift of the first observable (i.e., in our past light cone) Gamma Ray Burst (GRB) and calculate the GRB-rate redshift distribution of the Population III stars at very early times (z=20-60). Using the last 2 years of data from Swift we place an upper limit on the efficiency (\eta_{GRB}) of GRB production per solar mass from the first generation of stars. We find that the first observable GRB is most likely to have formed at redshift 60. The observed rate of extremely high redshift GRBs (XRGs) is a subset of a group of 15 long GRBs per year, with no associated redshift and no optical afterglow counterparts, detected by Swift. Taking this maximal rate we get that \eta_{GRB}<1.1~10^{-4} GRBs per solar mass in stars. A more realistic evaluation, e.g., taking a subgroup of 5% of the total sample of Swift gives an upper limit of \eta_{GRB}<3.2~10^{-5} GRBs per solar mass.Comment: 6 Pages, 3 figures, submitted to MNRA

Characterization of Benzoyl Saxitoxin Analogs from the Toxigenic Marine Dinoflagellate Gymnodinium catenatum by Hydrophilic Interaction Liquid Ion-Chromatography-Tandem Mass Spectrometry

The chain-forming marine dinoflagellate Gymnodinium catenatum Graham has a remarkable capacity to produce a wide array of neurotoxic alkaloids associated with Paralytic Shellfish Poisoning (PSP). More than a decade ago, a completely new group of benzoyl saxitoxin analogs produced exclusively by this species was discovered, but the exact structural assignments and diversity among global population has remained elusive and nconfirmed in most cases. In the current study, fifteen among eighteen hypothetical benzoyl analogs were partially purified and identified from cultured isolates of G. catenatum from the Pacific coast of Mexico. Combined serial application of flash chromatography, preparative liquid chromatography and tandem mass spectrometry (LC-MS/MS) in multiple steps yielded a richness of benzoyl analogs that has not been reported nor confirmed before. Two sub-fractions were analyzed by 1H-NMR; results from one fraction showed a probable AMX pattern for three protons, consistent with the presence of a 3,4-dihydroxylated benzoyl ring. These findings could be interpreted to correct the 2,4-dihydroxylated structure previously proposed for the GCa benzoyl analog series. The revised and enhanced structural information on proposed benzoyl derivatives is necessary to provide further insights into biogeographical diversity of these potentially potent toxins produced by marine dinoflagellates and their role in seafood safety

Gamma-Ray Bursts in 1.8<z<5.61.8 < z < 5.6 Suggest that the Time Variation of the Dark Energy is Small

We calibrated the peak energy-peak luminosity relation of GRBs (so called Yonetoku relation) using 33 events with the redshift $z < 1.62$ without assuming any cosmological models. The luminosity distances to GRBs are estimated from those of large amount of Type Ia supernovae with $z<1.755$. This calibrated Yonetoku relation can be used as a new cosmic distance ladder toward higher redshifts. We determined the luminosity distances of 30 GRBs in $1.8 < z < 5.6$ using the calibrated relation and plotted the likelihood contour in $(\Omega_m,\Omega_\Lambda)$ plane. We obtained $(\Omega_m, \Omega_{\Lambda})= (0.37^{+0.14}_{-0.11}, 0.63^{+0.11}_{-0.14})$ for a flat universe. Since our method is free from the circularity problem, we can say that our universe in $1.8 < z < 5.6$ is compatible with the so called concordance cosmological model derived for $z < 1.8$. This suggests that the time variation of the dark energy is small or zero up to $z\sim 6$.Comment: 4 pages, 4 figures, accepted to MNRA

Docking Simulation of the Binding Interactions of Saxitoxin Analogs Produced by the Marine Dinoflagellate Gymnodinium catenatum to the Voltage-Gated Sodium Channel Nav1.4

Saxitoxin (STX) and its analogs are paralytic alkaloid neurotoxins that block the voltage-gated sodium channel pore (Nav), impeding passage of Na+ ions into the intracellular space, and thereby preventing the action potential in the peripheral nervous system and skeletal muscle. The marine dinoflagellate Gymnodinium catenatum produces an array of such toxins, including the recently discovered benzoyl analogs, for which the mammalian toxicities are essentially unknown. We subjected STX and its analogs to a theoretical docking simulation based upon two alternative tri-dimensional models of the Nav1.4 to find a relationship between the binding properties and the known mammalian toxicity of selected STX analogs. We inferred hypothetical toxicities for the benzoyl analogs from the modeled values. We demonstrate that these toxins exhibit different binding modes with similar free binding energies and that these alternative binding modes are equally probable. We propose that the principal binding that governs ligand recognition is mediated by electrostatic interactions. Our simulation constitutes the first in silico modeling study on benzoyl-type paralytic toxins and provides an approach towards a better understanding of the mode of action of STX and its analogs

EVALUATION OF ANTI-INFLAMMATORY ACTIVITY OF MACROALGAE COLLECTED FROM BAJA CALIFORNIA SUR, MEXICO

Objective: This study aimed to establish the anti-inflammatory potential of macroalgae from Baja California Sur, Mexico. Methods: The anti-inflammatory activity of the extracts from 10 macroalgae species was evaluated in vitro and in vivo. Dichloromethane, ethanolic, and aqueous extracts were obtained from each species. The criteria used to determine anti-inflammatory activity included 1) the membrane protection of human red blood cells (HRBCs) against hemolysis induced by hypotonicity, 2) the inhibition of heat-induced protein denaturation (IDP), and 3) the inhibition of mouse ear edema and the myeloperoxidase (MPO) enzyme. Results: The dichloromethane extracts of Gracilaria vermiculophylla and Opuntiella californica were the most active, both in vitro and in vivo. These extracts resulted in values of HRBC membrane protection above 95%, which were similar to those obtained with diclofenac sodium. And reduce the inflammation with edema inhibition percentage up to 60 % while the control indomethacin was able to inhibit edema by 82.3 %. Conclusion: The bioprospection of several macroalgae species from Bahía de La Paz, Mexico, allowed the identification of two species with promising anti-inflammatory activity. Gracilaria vermiculophylla showed interesting topical anti-inflammatory effects and a profile of compounds (flavonoids and terpenes) that may contribute to the potential biological properties of this seaweed. This study represents the first report of the anti-inflammatory potential of O. californica

The 1st INTEGRAL SPI-ACS Gamma-Ray Burst Catalogue

We present the sample of gamma-ray bursts detected with the anti-coincidence shield ACS of the spectrometer SPI on-board INTEGRAL for the first 26.5 months of mission operation (up to Jan 2005). SPI-ACS works as a nearly omnidirectional gamma-ray burst detector above ~80 keV but lacks spatial and spectral information. In this catalogue, the properties derived from the 50 ms light curves (e.g., T90, Cmax, Cint, variability, V/Vmax) are given for each candidate burst in the sample. A strong excess of very short events with durations <0.25 s is found. This population is shown to be significantly different from the short- and long-duration burst sample by means of the intensity distribution and V/Vmax test and is certainly connected with cosmic ray hits in the detector. A rate of 0.3 true gamma-ray bursts per day is observed.Comment: 10 pages, 9 figures, A&A accepte

Studies in Astronomical Time Series Analysis. VI. Bayesian Block Representations

This paper addresses the problem of detecting and characterizing local variability in time series and other forms of sequential data. The goal is to identify and characterize statistically significant variations, at the same time suppressing the inevitable corrupting observational errors. We present a simple nonparametric modeling technique and an algorithm implementing it - an improved and generalized version of Bayesian Blocks (Scargle 1998) - that finds the optimal segmentation of the data in the observation interval. The structure of the algorithm allows it to be used in either a real-time trigger mode, or a retrospective mode. Maximum likelihood or marginal posterior functions to measure model fitness are presented for events, binned counts, and measurements at arbitrary times with known error distributions. Problems addressed include those connected with data gaps, variable exposure, extension to piecewise linear and piecewise exponential representations, multi-variate time series data, analysis of variance, data on the circle, other data modes, and dispersed data. Simulations provide evidence that the detection efficiency for weak signals is close to a theoretical asymptotic limit derived by (Arias-Castro, Donoho and Huo 2003). In the spirit of Reproducible Research (Donoho et al. 2008) all of the code and data necessary to reproduce all of the figures in this paper are included as auxiliary material.Comment: Added some missing script files and updated other ancillary data (code and data files). To be submitted to the Astophysical Journa

Influence of phytoplankton diets on the ingestion rate and egg production of Acartia clausi and A. lilljeborgii (Copepoda: Calanoida) from Bahía de La Paz, Gulf of California

Different phytoplankton diets were tested on Acartia clausi and A. lilljeborgii from Bahía de La Paz to determine their effect on survival, egg production, and ingestion rate. Female copepods were fed diatom strains (Chaetoceros sp., Cylindrotheca closterium, Odontella longicruris, and Dytilum brightwelli), dinoflagellate strains (Scrippsiella sp., Gyrodinium sp., Prorocentrum micans, and P. rhathymum), and one Raphidophyceae (Chattonella sp.). After 24 h of incubation in darkness at 24 °C, survival with various phytoplankton diets was above 91%. Gyrodinium sp. produced the lowest survival in both copepod species (44.5% in A. clausi and 89.6% in A. lilljeborgii). Dinoflagellate diets provided the highest egg production. A. clausi had higher egg production when fed with P. rhathymum, P. micans, Gyrodinium sp., Scrippsiella sp., and Chattonella sp. A. lilljeborgii had a higher egg production with Scrippsiella sp., P. micans, Gyrodinium sp., and Chaetoceros sp. Ingestion rates were higher in both Acartia species with two diatom diets (O. longicruris and Chaetoceros sp.), P. rhathymum and Chattonella sp. These results suggest that both Acartia species respond to nutritional quality of phytoplankton in a short time. Higher ingestion rates did not necessarily result in higher egg production, suggesting that the link between ingestion and egg production may be in what is eaten, rather than in how much. The response in egg production seems to be species specific, but in general was higher with dinoflagellate diets, suggesting a higher food quality compared with diatoms (excepting Chaetoceros sp.)