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Surface bloom-forming species, predominantly of the Dinophyceae, have the capacity to accumulate high amounts of mycosporine-like amino acids (MAAs). The 3 dinoflagellate species (Gonyaulacales, Dinophyceae), Alexandrium tamarense, A. catenella and A. minutum are bloom-forming toxic isolates. They are usually found forming blooms near the surface, hence, they are exposed to high light conditions. Using an improved HPLC methodology, 9 MAAs were separated and identified. Several forms of atypical MAAs, not previously reported in the literature, were also revealed. The chromatographic behaviour of these new compounds, UV spectra, chemical properties and mass spectra indicate that they contain 2 or more common MAAs linked among themselves. These atypical MAAs were present in the 3 Alexandrium species. At the same time, the chromatographic profile of A. minutum, A. tamarense and A. catenella, showed great differences. The biochemical composition of the cells is highly variable with growth conditions. Hence, we also reported, for the sake of a comparative discussion, the toxin and pigment composition of these Alexandrium isolates. The 3 species showed the same pigment pattern characteristic of peridinin-containing dinoflagellates. On the contrary, as reported previously, great variation of the toxin profiles was observed among the Alexandrium species. We conclude that, although MAAs are common among phytoplankton, the occurrence of different types of novel MAAs in the 3 Alexandrium species studied here would indicate some degree of biogeographic or ecotypic diversification.

The in vitro photoinduced reactions of the mycosporine-like amino acids (MAA) usujirene and palythene were studied by monochromatic stationary irradiation at 366 nm. High-performance liquid chromatography analysis of the irradiated aqueous solution of usujirene indicated a low photoreactivity on the basis of the observed photodecomposition quantum yield of ϕ−U = (2.86 ± 0.80) × 10−5, which can be partially accounted for by the cis–trans photoisomerization of usujirene to palythene (ϕU→P = [1.71 ± 0.13] × 10−5). However, palythene in aqueous solution showed a higher photostability than did usujirene under equivalent conditions, establishing a photostationary mixture of cis–trans isomers with a relative composition of palythene–usujirene (11:1). These results may explain the preferential in vivo accumulation of palythene relative to that of usujirene observed in several dinoflagellate species.

Taxonomically diverse marine, freshwater and terrestrial organisms have evolved the capacity to synthesize, accumulate and metabolize a variety of UV-absorbing substances called mycosporine-like amino acids (MAAs) as part of an overall strategy to diminish the direct and indirect damaging effects of environmental ultraviolet radiation (UVR). Whereas the enzymatic machinery to synthesize MAAs was probably inherited from cyanobacteria ancestors via the endosymbionts hypothesis, metazoans lack this biochemical pathway, but can acquire and metabolize these compounds by trophic transference, symbiotic or bacterial association. In this review we describe the structure and physicochemical properties of MAAs, including the recently discovered compounds and the modern methods used for their isolation and identification, updating previous reviews. On this basis, we review the metabolism and distribution of this unique class of metabolites among marine organism.

Surface bloom-forming species, predominantly of the Dinophyceae, have the capacity to accumulate high amounts of mycosporine-like amino acids (MAAs). The 3 dinoflagellate species (Gonyaulacales, Dinophyceae),Alexandrium tamarense(Lebour) Balech,A. catenella(Weedon et Kofoid) Balech, andA. minutumHalim, are bloom-forming toxic isolates. They are usually found forming blooms near the surface, hence, they are exposed to high light conditions. Using an improved HPLC methodology, 9 MAAs were separated and identified. Several forms of atypical MAAs, not previously reported in the literature, were also revealed. The chromatographic behaviour of these new compounds, UV spectra, chemical properties and mass spectra indicate that they contain 2 or more common MAAs linked among themselves. These atypical MAAs were present in the 3Alexandriumspecies. At the same time, the chromatographic profile ofA. minutum, A. tamarenseandA. catenella, showed great differences. The biochemical composition of the cells is highly variable with growth conditions. Hence, we also reported, for the sake of a comparative discussion, the toxin and pigment composition of theseAlexandriumisolates. The 3 species showed the same pigment pattern characteristic of peridinin-containing dinoflagellates. On the contrary, as reported previously, great variation of the toxin profiles was observed among theAlexandriumspecies. We conclude that, although MAAs are common among phytoplankton, the occurrence of different types of novel MAAs in the 3Alexandriumspecies studied here would indicate some degree of biogeographic or ecotypic diversification.

The in vitro photoinduced reactions of the mycosporine‐like amino acids (MAA) usujirene and palythene were studied by monochromatic stationary irradiation at 366 nm. High‐performance liquid chromatography analysis of the irradiated aqueous solution of usujirene indicated a low photoreactivity on the basis of the observed photodecomposition quantum yield of ϕ−U= (2.86 ± 0.80) × 10−5, which can be partially accounted for by the cis–trans photoisomerization of usujirene to palythene (ϕU→P=[1.71 ± 0.13]× 10−5). However, palythene in aqueous solution showed a higher photostability than did usujirene under equivalent conditions, establishing a photostationary mixture of cis–trans isomers with a relative composition of palythene–usujirene (11:1). These results may explain the preferential in vivo accumulation of palythene relative to that of usujirene observed in several dinoflagellate species.

The in vitro photoinduced reactions of the mycosporine-like amino acids (MAA) usujirene and palythene were studied by monochromatic stationary irradiation at 366 nm. High-performance liquid chromatography analysis of the irradiated aqueous solution of usujirene indicated a low photoreactivity on the basis of the observed photodecomposition quantum yield of phi(-U) = (2.86 +/- 0.80) x 10(-5), which can be partially accounted for by the cis-trans photoisomerization of usujirene to palythene (phi(U-->P) = [1.71 +/- 0.13] x 10(-5)). However, palythene in aqueous solution showed a higher photostability than did usujirene under equivalent conditions, establishing a photostationary mixture of cis-trans isomers with a relative composition of palythene-usujirene (11:1). These results may explain the preferential in vivo accumulation of palythene relative to that of usujirene observed in several dinoflagellate species.

Description and role of MAAsIt is now generally believed that natural ultraviolet-A radiation (UV-A, 315–400 nm) and ultraviolet-B radiation (UV-B, 280–315 nm) are strong environmental factors affecting both productivity and community structure in marine and terrestrial ecosystems (de Mora et al., 2000). Reduction of the stratospheric ozone layer, which has caused an increase in the UV-B flux to the Earth's surface in recent years (Farman et al., 1985), could result in increased levels of UV-induced damage for most living organisms (Vincent and Neale, 2000), producing a great impact on the photosynthetic carbon fixation by plants and, consequently, on the global climate change (UNEP, 2006). At the beginning of the evolution of life on Earth, UV-B flux rates clearly exceeded the present values (Cockell and Horneck, 2001) resulting in the evolution of several protection strategies to counteract the negative effects of UV radiation (Roy, 2000). One of the adaptations whereby phytoplankton can reduce UV-induced damage is the synthesis of compounds that can absorb the damaging wavelengths and dissipate the absorbed energy without generating phototoxic reactive intermediates. A variety of such compounds have been found in aquatic and terrestrial plants (Rozema et al., 2002).As early as 1938 there were observations of UV-absorbing compounds in marine algae (Kalle, 1938; referenced in Sivalingam et al., 1974). This was followed in 1969 by reports of UV-absorbing substances (named S-320) in water extracts from several species of corals and a cyanobacterium (most likely Trichodesmium) from the Great Barrier Reef (Shibata, 1969). Mycosporine-like amino acids (MAAs) from marine organisms were first isolated and characterized by Hirata and co-workers (Hirata et al., 1979). They isolated and characterized mycosporine-glycine from the tropical zoanthid Palythoa tuberculosa (Ito and Hirata, 1977), a compound previously isolated from mycelia of sporulating fungi (Favre-Bonvin et al., 1976), and then described several related imine derivatives of mycosporines (Hirata et al., 1979). Since then, more than 20 closely related MAA compounds have been isolated and characterized from several plants and marine animals (Figure 10.1 and Table 10.1). Wide ranging studies indicate that these compounds occur in virtually all taxa of marine and freshwater cyanobacteria and algae, in invertebrate–microbial symbioses and in metazoans (Karentz et al., 1991; Gröniger et al., 2000; Karentz, 2001).

Results from a multidisciplinary environmental cruise carried out in the Common Fishing Zone (ZCP by its Spanish acronym) on board the BIP 'Cap. Oca Balda' (25th March - 1st April 2014) are presented. Sampling was conducted along two transects on the continental shelf from the coastal sector (COS) through the shelf-break (TAL) and beyond, at the latitudes of Mar del Plata (Argentina) and La Paloma (Uruguay). These transects were identified as COSTAL I and COSTAL II respectively, comprising six stations each. The same sequence of activities was performed at each station, starting by measurements of temperature, salinity, fluorescence and light penetration profiles, followed by water sampling with Niskin bottles. These water samples were used for the analyses of nutrients, dissolved oxygen, total alkalinity - dissolved inorganic carbon, absorption by particulate and chromophoric dissolved organic matter (CDOM), concentration of total chlorophyll a (ClaT ) and the concentration due to the phytoplankton fraction smaller than 5 mu m (Cla<5), pigment composition, bacterioplankton abundance, search and counting of entheropathogenic microorganisms, hydrocarbon degrading bacteria (BDH), and all phytoplankton fractions. Finally, tows with different plankton nets were also performed: Bongo (67 and 200 mu m), Bongo (300 mu m) and Nackthai (400 mu m).Original Abstract: En este trabajo se presentan resultados de una campana ambiental multidisciplinaria realizada en la Zona Comun de Pesca (ZCP) en el BIP 'Cap. Oca Balda' (25 de Marzo al 1 de Abril de 2014). Los muestreos se distribuyeron en dos secciones en la plataforma continental desde el sector costero (COS) hasta trasponer el talud continental (TAL), a las latitudes de Mar del Plata (Argentina) y La Paloma (Uruguay), denominandose COSTAL I y COSTAL II, respectivamente. En cada una se ubicaron seis estaciones, en las que se siguio una misma secuencia de actividades comenzando con la adquisicion de los perfiles de temperatura, salinidad, fluorescencia y penetracion de luz. Luego, se tomaron muestras de agua con botellas 'Niskin', las cuales se utilizaron para analizar nutrientes, oxigeno disuelto, alcalinidad total - carbono inorganico disuelto, absorcion del material particulado y del organico disuelto coloreado (CDOM), concentracion de clorofila a total (ClaT ) y la debida a la fraccion del fitoplancton menor a 5 mu m (Cla<5), diversidad de pigmentos, abundancia del bacterioplancton, busqueda y recuento de microorganismos enteropatogenos, bacterias degradadoras de hidrocarburos (BDH) y de todas las fracciones del fitoplancton. Finalmente, se realizaron muestreos con diferentes redes de plancton: mini-Bongo (67 y 200 mu m), Bongo (300 mu m) y Nackthai (400 mu m).