Photocatalytic properties of nanocrystalline titanium dioxide films in the degradation of domoic acid in aqueous solution: potential for use in molluscan shellfish biotoxin depuration facilities.

Domoic acid (DA) is a water-soluble marine neurotoxin produced and released by certain species of the diatom genus Pseudo-nitzschia. Present in coastal waters, it can be a threat to public health and marine life, and can result in severe economic losses to the molluscan shellfish and crustacean harvesting industries. Here we report on the efficiency of nanocrystalline (NC) titania (TiO(2)) thin films used as a photocatalyst in the ultraviolet light photodegradation of DA. Titanium dioxide thin films produced by a sol-gel dip-coating method in the presence of polyethylene glycol of different molecular weights (200, 400 and 600) were deposited on glass substrates and crystallised at 90 degrees C. The films were characterised using spectroscopic ellipsometry, Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The photocatalytic activity measurements were carried out by immersing the NC TiO(2) films in a DA solution (2500 ng ml(-1)) and then exposing them for various times at room temperature to UVA irradiation (lambda = approximately 350 nm). The degradation of DA, quantified by HPLC analysis, was not significant when using daylight or ultraviolet light irradiation alone, whereas the NC TiO(2) films prepared at low temperature proved to be a very efficient photocatalyst when used in conjunction with UVA light. The effectiveness of the photodegradation was improved by increasing molecular weight of polyethylene glycol, which increased the thickness of the film. The presence, transformation and degradation of three DA isomers were observed. The approach may eventually be practical for destroying DA in seawater used by aquaculture industry depuration facilities.

Environmental stress and domoic acid production by Pseudo-nitzschia: a physiological perspective.

Production of domoic acid (DA) by the pennate diatom Pseudo-nitzschia multiseries is associated with physiological stress caused by silicate (Si) and/or phosphate (P) limitation. Such limitation may promote DA synthesis by (1) reducing primary metabolic activity, thus making available necessary precursors, high energy compounds, and cofactors, and (2) favoring the expression of genes involved in the biosynthesis of this toxin. In the case of Si and P-limitation, DNA synthesis and the progression through the cell division cycle are slowed, perhaps prolonging or arresting the cells in the stage of the division cycle which is most conducive to DA production. However, N-limitation results in an insufficient pool of cellular free N, which restricts synthesis of this nitrogenous toxin. A continuous supply of photophosphorylated high-energy intermediates (e.g., ATP and NADPH) is necessary for DA synthesis. In order to better understand the mechanism(s) of DA production, more studies are needed to elucidate: (1) the details of the biosynthetic pathway, (2) the regulation of enzymes involved in the pathway, (3) the relation between DA synthesis and the cell division cycle, (4) the cellular compartmentalization of DA biosynthesis, and (5) other environmental factors that may trigger DA production. Finally, these studies should be extended to include toxigenic Pseudo-nitzschia species other than P. multiseries, to confirm the commonality of these mechanisms.

Enhancement of domoic acid production by reintroducing bacteria to axenic cultures of the diatom Pseudo-nitzschia multiseries.

Axenic cultures of Pseudo-nitzschia multiseries (formerly Pseudonitzschia pungens f. multiseries) produce less domoic acid (DA) than the original bacteria-containing cultures. Bacterial strains isolated from two nonaxenic P. multiseries clones were reintroduced individually into cultures of three axenic P. multiseries strains. The bacteria did not substantially affect division rates or cell yields. However, they did cause a 2- to 95-fold enhancement of DA production (per cell basis) relative to the axenic culture, depending on the P. multiseries and bacterial strain used. Bacteria isolated from a nontoxic Chaetoceros sp. culture also enhanced DA per cell (by 115-fold), showing that it is not necessary for the bacteria to be isolated from a toxic culture in order to enhance toxin production. There was no evidence of intracellular bacteria in disrupted P. multiseries cells obtained from axenic cultures. Our results demonstrate an important, but nonessential, role of extracellular bacterial in DA production. Characterization of the bacterial strains using morphology, substrate utilization, and restriction fragment length polymorphism (RFLP) analyses clearly showed that we had isolated different species of bacteria from the various nonaxenic cultures. We conclude that not one but several bacterial species enhance DA production by P. multiseries.

Reconstruction of genealogies from vital records: the Laredo Epidemiology Project.

The Laredo Epidemiology Project is a study of the patterns of degenerative disease, particularly cancer, in the families of Laredo, Texas. The genealogical history of Laredo was reconstructed by the grouping of 350,000 individual church and civil vital event records into multigenerational families, with record linkage based on matching names. Mortality data from city death records are mapped onto these pedigrees for analysis. This paper describes the creation of the data base and evaluation of the links.