Description: Seawater samples were collected in four stations along a cross-shore transect in front of the Port of Mazatlán (Mexico) during the oceanographic cruise Maz V (April 2019) on board the R/V “El Puma” (UNAM). Samples were collected at different depths based on the oxygen and chlorophyll-a profiles: surface (5 m depth); mixed layer, deep chlorophyll maximum (at 10–45 m depth); oxycline, base of the oxycline (at 60–125 m depth); upper OMZ; OMZ core (at 250 m depth); and bottom (between 23 m depth in S1 and 670 m depth in S4). Total N and P were determined using a Skalar San-Plus segmented-flow autoanalyzer. Dissolved gases were analyzed through the addition of 5 mL of ultrapure helium into the vials to generate a static-headspace equilibration. N2O was analyzed with a Varian 3380 gas chromatograph using an electron capture detector. CH4 was analyzed with a Schimadzu 17A gas chromatograph with a flame ionization detector and a capillary column.

Description: Hydrographic data and seawater samples were collected in four stations along a cross-shore transect in front of the Port of Mazatlán (Mexico) during the oceanographic cruises Maz IV (April 2018) and Maz V (April 2019) on board the R/V “El Puma” (UNAM). Temperature, dissolved oxygen, salinity, and chlorophyll-a fluorescence profiles were measured with a SBE-19plus CTD probe equipped with a WET labs fluorometer sensor. Seawater samples for nutrient analyses were collected at different depths based on the oxygen and chlorophyll-a profiles: surface (5 m depth); mixed layer, deep chlorophyll maximum (at 10–45 m depth); oxycline, base of the oxycline (at 60–125 m depth); upper OMZ (only for Maz V); OMZ core (at 250 m depth); and bottom (between 23 m depth in S1 and 670 m depth in S4). Seawater samples were filtered through cellulose acetate syringe filters (0.22-μm pore, Merck Millipore) and nutrient analyses were determined using a Skalar San-Plus segmented-flow autoanalyzer.

Description: Seawater samples were collected with 10-L Niskin bottles in four stations along a cross-shore transect in front of the Port of Mazatlán (Mexico) during the oceanographic cruises Maz IV (April 2018) and Maz V (April 2019) on board the R/V “El Puma” (UNAM). Samples for molecular analyses (16S rRNA sequences) were collected at different depths based on the oxygen and chlorophyll-a profiles: surface (5 m depth); deep chlorophyll maximum (at 10–45 m depth, except in the coastal station S1 of Maz V where a sample was collected at the mixed layer); base of the oxycline (at 60–125 m depth); OMZ core (only for Maz IV at 250 m depth); and bottom (between 23 m depth in S1 and 670 m depth in S4). Water samples were filtered on board through polycarbonate membranes (0.22-μm pore, Merck Millipore). Genomic DNA was extracted with the DNeasy PowerWater Kit (Qiagen). The V3–V4 region of the 16S rRNA gene was amplified using the index and adaptor-linked primers Bakt_341F and Bakt_805R, and then sequenced using a 2 × 300 bp paired-end Illumina Miseq system. Amplicon libraries were analyzed with the software QIIME 2.

Description: Seawater samples were collected with 10-L Niskin bottles in four stations along a cross-shore transect in front of the Port of Mazatlán (Mexico) during the oceanographic cruises Maz IV (April 2018) and Maz V (April 2019) on board the R/V "El Puma" (UNAM). Samples for molecular analyses (abundance of N-cycling genes) were collected at different depths based on the oxygen and chlorophyll-a profiles: surface (5 m depth); mixed layer, deep chlorophyll maximum (at 10–45 m depth); oxycline, base of the oxycline (at 60–125 m depth); upper OMZ (only for Maz V); OMZ core (at 250 m depth); and bottom (between 23 m depth in S1 and 670 m depth in S4). Water samples were filtered on board through polycarbonate membranes (0.22-μm pore, Merck Millipore). Genomic DNA was extracted with the DNeasy PowerWater Kit (Qiagen). The abundance of N-cycling genes was assessed using the gene copy number of bacterial and archaeal amoA, anammox bacterial 16S rRNA, nirK, nirS, and nrfA, using a StepOnePlus real-time PCR system (Applied Biosystems).

Description: The dinoflagellate genus Prorocentrum is globally represented by a wide variety of species found upon benthic and/or epiphytic substrates. Many epibenthic Prorocentrum species produce lipophilic polyether toxins, some of which act as potent protein phosphatase inhibitors and tumor-promoters associated with Diarrheic Shellfish Poisoning (DSP). Most members of the Prorocentrum lima species complex (PLSC) commonly found in the tropics and sub-tropics are toxigenic. Epiphytic and planktonic bacteria co-occur with toxigenic Prorocentrum but reciprocal allelochemical interactions are under-investigated. The aim of the present study was to identify the culturable bacteria collected together with isolates of the PLSC from seagrass (Thalassia testudinum) and macroalgae along tropical Atlantic coasts of Mexico, and to explore potential species interactions with selected isolates. Twenty-one bacterial genera belonging to Proteobacteria, Actinobacteria, and Bacteroidetes were identified by amplification of the 16S rRNA gene marker from nine clonal Prorocentrum cultures, with g-proteobacteria comprising the dominant class. A positive correlation was found between the bacterial genera associated with two Prorocentrum clones and the esterified toxin analog DTX1a-D8, but there was no apparent correlation between the other PLSC clones and their associated bacteria with the other five DSP toxins detected. No bacteriostatic or allelochemical response was found for cell- and culture medium extracts of five Prorocentrum isolates assayed for bioactivity against Staphylococcus sp. DMBS2 and Vibrio sp. HEL66. Bulk cell-washing of Prorocentrum PA1, followed by growth with antibiotics, was only effective in reducing bacterial load in the initial growth stages, but did not yield axenic cultures or lower bacterial cell densities throughout the culture cycle. Antibiotic treatment did not impair growth or survival of the dinoflagellate, or apparently affect DSP toxin production. There was no significant correlation between Prorocentrum cell volume, growth rate, bacterial cell counts, or cellular toxin concentration over the entire time-series culture cycle. Benthic Prorocentrum and associated bacterial communities comprise highly diverse and characteristic microbiomes upon substrates, and among compartments in culture, but this study provides little evidence that allelochemical interactions among Prorocentrum cells and associated bacteria originating from epibenthic substrates play a definable role in growth and toxigenicity.