Measuring Marine Biotoxins in a Hypersaline Coastal Lagoon.

Marine biotoxins have posed a persistent problem along various coasts for many years. Coastal lagoons are ecosystems prone to phytoplankton blooms when altered by eutrophication. The Mar Menor is the largest hypersaline coastal lagoon in Europe. Sixteen marine toxins, including lipophilic toxins, yessotoxins, and domoic acid (DA), in seawater samples from the Mar Menor coastal lagoon were measured in one year. Only DA was detected in the range of 44.9-173.8 ng L-1. Environmental stressors and mechanisms controlling the presence of DA in the lagoon are discussed. As an enrichment and clean-up method, we employed solid phase extraction to filter and acidify 75 mL of the sample, followed by pre-concentration through a C18 SPE cartridge. The analytes were recovered in aqueous solutions and directly injected into the liquid chromatography system (LC-MS), which was equipped with a C18 column. The system operated in gradient mode, and we used tandem mass spectrometry (MS/MS) with a triple quadrupole (QqQ) in the multiple reaction monitoring mode (MRM) for analysis. The absence of matrix effects was checked and the limits of detection for most toxins were low, ranging from 0.05 to 91.2 ng L-1, depending on the compound. To validate the measurements, we performed recovery studies, falling in the range of 74-122%, with an intraday precision below 14.9% RSD.

Free and glycosylated aroma compounds in grapes monitored by solid-liquid extraction and dispersive liquid-liquid microextraction combined with gas chromatography-mass spectrometry.

Fifteen aroma compounds have been determined in their free and glycosylated forms in grapes using dispersive liquid-liquid microextraction with gas chromatography-mass spectrometry. The sample treatment includes a previous solid-liquid extraction stage and subsequent parallel microextraction approaches to preconcentrate total aroma content and the free fraction. Thus, the extraction of the total content of analytes requires previous enzymatic hydrolysis of the bound forms. For preconcentration, chloroform (250 µl) and acetonitrile (1.5 ml) were added to 10 ml of the sample extract in the presence of 0.5 g sodium chloride. The absence of matrix effect in the samples allowed quantification against aqueous external standards. Limits of detection ranged between 5 and 30 ng/g, depending on the compound. Method accuracy was studied through recovery assays, with recoveries in the 82-115% range being obtained. Relative standard deviations for repeatability studies were lower than 12%. Four different samples of grapes were analyzed, being quantified linalool in its free form at concentrations in the 359-470 ng/g range, and benzyl alcohol, 2-phenylethanol, and linalool oxide I and II in their bound forms between 52 and 464 ng/g.

Depth Profile of Nitrifying Archaeal and Bacterial Communities in the Remote Oligotrophic Waters of the North Pacific.

Nitrification is a vital ecosystem function in the open ocean that regenerates inorganic nitrogen and promotes primary production. Recent studies have shown that the ecology and physiology of nitrifying organisms is more complex than previously postulated. The distribution of these organisms in the remote oligotrophic ocean and their interactions with the physicochemical environment are relatively understudied. In this work, we aimed to evaluate the depth profile of nitrifying archaea and bacteria in the Eastern North Pacific Subtropical Front, an area with limited biological surveys but with intense trophic transferences and physicochemical gradients. Furthermore, we investigated the dominant physicochemical and biological relationships within and between ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) as well as with the overall prokaryotic community. We used a 16S rRNA gene sequencing approach to identify and characterize the nitrifying groups within the first 500 m of the water column and to analyze their abiotic and biotic interactions. The water column was characterized mainly by two contrasting environments, warm O2-rich surface waters with low dissolved inorganic nitrogen (DIN) and a cold O2-deficient mesopelagic layer with high concentrations of nitrate (NO3 -). Thaumarcheotal AOA and bacterial NOB were highly abundant below the deep chlorophyll maximum (DCM) and in the mesopelagic. In the mesopelagic, AOA and NOB represented up to 25 and 3% of the total prokaryotic community, respectively. Interestingly, the AOA community in the mesopelagic was dominated by unclassified genera that may constitute a novel group of AOA highly adapted to the conditions observed at those depths. Several of these unclassified amplicon sequence variants (ASVs) were positively correlated with NO3 - concentrations and negatively correlated with temperature and O2, whereas known thaumarcheotal genera exhibited the opposite behavior. Additionally, we found a large network of positive interactions within and between putative nitrifying ASVs and other prokaryotic groups, including 13230 significant correlations and 23 sub-communities of AOA, AOB, NOB, irrespective of their taxonomic classification. This study provides new insights into our understanding of the roles that AOA may play in recycling inorganic nitrogen in the oligotrophic ocean, with potential consequences to primary production in these remote ecosystems.

Monitoring Lipophilic Toxins in Seawater Using Dispersive Liquid-Liquid Microextraction and Liquid Chromatography with Triple Quadrupole Mass Spectrometry.

The use of dispersive liquid-liquid microextraction (DLLME) is proposed for the preconcentration of thirteen lipophilic marine toxins in seawater samples. For this purpose, 0.5 mL of methanol and 440 µL of chloroform were injected into 12 mL of sample. The enriched organic phase, once evaporated and reconstituted in methanol, was analyzed by reversed-phase liquid chromatography with triple-quadrupole tandem mass spectrometry. A central composite design multivariate method was used to optimize the interrelated parameters affecting DLLME efficiency. The absence of any matrix effect in the samples allowed them to be quantified against aqueous standards. The optimized procedure was validated by recovery studies, which provided values in the 82-123% range. The detection limits varied between 0.2 and 5.7 ng L-1, depending on the analyte, and the intraday precision values were in the 0.1-7.5% range in terms of relative standard deviation. Ten water samples taken from different points of the Mar Menor lagoon were analyzed and were found to be free of the studied toxins.