Modelling the Stoichiometric Regulation of C-Rich Toxins in Marine Dinoflagellates

Toxin production in marine microalgae was previously shown to be tightly coupled with cellular stoichiometry. The highest values of cellular toxin are in fact mainly associated with a high carbon to nutrient cellular ratio. In particular, the cellular accumulation of C-rich toxins (i.e., with C:N > 6.6) can be stimulated by both N and P deficiency. Dinoflagellates are the main producers of C-rich toxins and may represent a serious threat for human health and the marine ecosystem. As such, the development of a numerical model able to predict how toxin production is stimulated by nutrient supply/deficiency is of primary utility for both scientific and management purposes. In this work we have developed a mechanistic model describing the stoichiometric regulation of C-rich toxins in marine dinoflagellates. To this purpose, a new formulation describing toxin production and fate was embedded in the European Regional Seas Ecosystem Model (ERSEM), here simplified to describe a monospecific batch culture. Toxin production was assumed to be composed by two distinct additive terms; the first is a constant fraction of algal production and is assumed to take place at any physiological conditions. The second term is assumed to be dependent on algal biomass and to be stimulated by internal nutrient deficiency. By using these assumptions, the model reproduced the concentrations and temporal evolution of toxins observed in cultures of Ostreopsis cf. ovata, a benthic/epiphytic dinoflagellate producing C-rich toxins named ovatoxins. The analysis of simulations and their comparison with experimental data provided a conceptual model linking toxin production and nutritional status in this species. The model was also qualitatively validated by using independent literature data, and the results indicate that our formulation can be also used to simulate toxin dynamics in other dinoflagellates. Our model represents an important step towards the simulation and prediction of marine algal toxicity

Clinical checklists in the selection of mentally retarded males for molecular screening of fragile X syndrome

Fragile X syndrome is the most frequent cause of inherited mental retardation. The phenotype in this syndrome is quite variable and less conspicuous in younger patients, making clinical diagnosis difficult and thus making molecular diagnosis necessary. The use of clinical checklists in mentally retarded individuals can help selecting patients to be given priority in the molecular investigation for the fragile-X mutation in the FMR1 gene. We evaluated two clinical checklists in a sample of 200 Brazilian male patients with mental retardation. The highest scores in the two checklists concentrated among the 19 males (9.5%) found to carry full mutations. Our results confirm the importance of fragile-X checklists as a clinical tool in the study of mentally retarded patients.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Universidade Federal de São Paulo (UNIFESP)Universidade de São Paulo Instituto de Biociências Departamento de Genética e Biologia EvolutivaUNIFESPSciEL

Assimilation of inorganic nitrogen for scaling up Desmodesmus communis (Scenedesmaceae) biomass production.

The feasibility of the green alga Desmodesmus communis for biomass production was investigated, firstly testing different nitrogen forms in the growth medium and the effect of CO2-enriched air supply, secondarily scaling up the cultivation system in 70 L photobioreactors (PBRs). Maximum nitrogen uptake rate obtained in the performed kinetic experiment was higher for ammonium than for nitrate (188.0 vs 11.7 \u3bcmol g 121 h 121); however, D. communis cultured in PBRs with only aeration grew faster with nitrate reaching a biomass yield (1.23 g L 121) and a productivity (0.036 g L 121 day 121) about twofold higher than with ammonium, which caused a pH decrease in the medium affecting the algal growth. CO2 supply allowed algal growth optimization, maintaining a high productivity with both nitrogen sources, slightly higher with nitrate (0.050 vs 0.038 g L 121 ay 121). Additionally, nitrate-supplied cells showed higher lipids (19.0 vs 9.4%) and proteins (33.0 vs 27.2%) values than those grown with ammonium. The semi-continuous scaled-up cultivation performed for 5 months attests the potential utilization of this species for valuable algal biomass production exploitable in various industrial applications

Preliminary results on phylogenetic structure of the bacterial community associated with Ostreopsis cf. ovata in batch cultures.

Extensive blooms of the toxic epiphytic/benthic dinoflagellate Ostreopsis cf. ovata are being reported with increase frequency and spatial distribution in temperate coastal regions including the Mediterranean Sea. O. cf. ovata outbreaks are of human and environmental health concern due to the production of isobaric palytoxin and a wide range of ovatoxins. In the last years, among the ecological factors that trigger or regulate the algal bloom dynamics, bacteria-microalgae interactions have received increasingly attention. This study investigated the microbial dynamics and the phylogenetic structure of the bacterial community co-occurring with Ostreopsis cf. ovata in batch cultures during different algal growth phases. Cultures of a O. cf. ovata strain isolated along the NW Adriatic Sea were maintained under controlled conditions for a period of 42 days. O. cf. ovata, bacterial cell abundances were monitored along with removal of major nutrients from the medium. Phylogenetic composition of bacterial community was assessed by next generation sequencing of bacterial 16S rDNA hypervariable regions. Bacterial growth showed two different exponential steps, the first step occurring in parallel with the algal exponential phase and the second one in concomitance with the algal mid-stationary phase. Ion torrent data revealed the presence of 12 bacterial phyla, 17 classes and 150 genera all along the experiment. A self-sufficient consortium for vitamin synthesis composed by only few genera belonging to Alphaproteobacteria (65-96%) and Sphingobacteria (2-34%) dominated the community. Our results allow to postulate on specific mutualistic and antagonistic interactions between O. cf. ovata and the associated microbial community in batch cultures, which ultimately will affect algal cellular physiology and potentially toxin dynamics. Moreover, the data pave the way for further investigations on relationships between bacteria-O. cf. ovata interactions and vitamins availability in the environment

Dynamics and sources of organic carbon in suspended particulate matter and sediments in Pialassa Baiona lagoon (NW Adriatic Sea, Italy)

Organic carbon (OC), total nitrogen (TN) and stable carbon isotopic signature (d13C) of suspended particulate matter and of surface sediments were investigated to assess temporal dynamics and relative contribution of autochthonous and allochthonous OC sources in the coastal eutrophic Pialassa Baiona lagoon. Water sampling for particulate organic carbon (POC), total nitrogen (PTN), nutrients and chlorophyll a (Chl a) concentrations, and bacterial abundance was carried out over a year. Seasonal changes of d13C POC signature and C/N ratio discriminated two main areas within the lagoon: the partially preserved northern-central area and the southernmost impacted area. Except for the southernmost impacted area, d13C POC (mean value: -22.11 per mil) showed the highest depleted values in winter and the most enriched in summer following phytoplankton seasonal development as also suggested by changes in C/N ratios, and by the significant correlations found between Chl a and POC, and d13C POC. Moreover, the two areas showed different timing and isotopic signature of phytoplankton blooms (e.g. Chl a 23.22 and 29.27 mg L-1, and d13C POC -19.15 and -30.70 per mil, June and March, in the northern-central and southern area, respectively). The summer bloom in the northern-central area was also associated with high bacterial abundances (up to 7.30 x 109 cells L-1), suggesting the establishment of a strong structured microbial food loop and organic matter recycling. Surface sediments from the southern impacted area showed significant higher values in OC and TN contents (3.05 and 1.44 %), and significant depleted d13C signal (-23.03 per mil) when compared to the control area (1.09 and 0.16 %, -19.40 per mil); whereas no differences were found in C/N ratios (8.1 and 8.2, in northern-central and southern impacted area, respectively). Elemental and isotopic composition data showed a strong coupling between POC and surface sediments. The relative contribution of three different sources (marine, estuarine, terrestrial) to POC and surface sediments were estimated using a mixing model, which predicted a predominant fraction of marine phytoplankton in POC during spring-summer and in surface sediments from the northern-central area. Conversely, dominant allochthonous sources were predicted for POC in winter months and in impacted area sediments. d13C values of surface sediment reflected an isotopic overprint of refractory terrestrial-derived (allochthonous) organic carbon agreeing with urban/industrial wastewaters origin