3 research outputs found

    Supplementary Material for: Photometric Determination of Ammonium and Phosphate in Seawater Medium Using a Microplate Reader

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    <p>To more efficiently process the large sample numbers for quantitative determination of ammonium (NH<sub>4</sub><sup>+</sup>) and phosphate (orthophosphate, PO<sub>4</sub><sup>3-</sup>) generated during comprehensive growth experiments with the marine <i>Roseobacter</i> group member<i> Phaeobacter inhibens</i> DSM 17395, specific colorimetric assays employing a microplate reader (MPR) were established. The NH<sub>4</sub><sup>+</sup> assay is based on the reaction of NH<sub>4</sub><sup>+</sup> with hypochlorite and salicylate, yielding a limit of detection of 14 µM, a limit of quantitation of 36 µM, and a linear range for quantitative determination up to 200 µM. The PO<sub>4</sub><sup>3-</sup>assay is based on the complex formation of PO<sub>4</sub><sup>3-</sup> with ammonium molybdate in the presence of ascorbate and zinc acetate, yielding a limit of detection of 13 µM, a limit of quantitation of 50 µM, and a linear range for quantitative determination up to 1 mM. Both MPR-based assays allowed for fast (significantly lower than 1 h) analysis of 21 samples plus standards for calibration (all measured in triplicates) and showed only low variation across a large collection of biological samples.</p

    Non-Redfield, nutrient synergy and flexible internal elemental stoichiometry in a marine bacterium.

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    The stoichiometric constraints of algal growth are well understood, whereas there is less knowledge for heterotrophic bacterioplankton. Growth of the marine bacterium Phaeobacter inhibens DSM 17395, belonging to the globally distributed Roseobacter group, was studied across a wide concentration range of NH 4 + and PO 4 3- . The unique dataset covers 415 different concentration pairs, corresponding to 207 different molar N:P ratios (from 10 -2 to 10 5 ). Maximal growth (by growth rate and biomass yield) was observed within a restricted concentration range at N:P ratios (50-120) markedly above Redfield. Experimentally determined growth parameters deviated to a large part from model predictions based on Liebig&#39;s law of the minimum, thus implicating synergistic co-limitation due to biochemical dependence of resources. Internal elemental ratios of P. inhibens varied with external nutrient supply within physiological constraints, thus adding to the growing evidence that aquatic bacteria can be flexible in their internal elemental composition. Taken together, the findings reported here revealed that P. inhibens is well adapted to fluctuating availability of inorganic N and P, expected to occur in its natural habitat (e.g. colonized algae, coastal areas). Moreover, this study suggests that elemental variability in bacterioplankton needs to be considered in the ecological stoichiometry of the oceans

    The marine bacterium Phaeobacter inhibens secures external ammonium by rapid buildup of intracellular nitrogen stocks.

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    Reduced nitrogen species are key nutrients for biological productivity in the oceans. Ammonium is often present in low and growth-limiting concentrations, albeit peaks occur during collapse of algal blooms or via input from deep sea upwelling and riverine inflow. Autotrophic phytoplankton exploit ammonium peaks by storing nitrogen intracellularly. In contrast, the strategy of heterotrophic bacterioplankton to acquire ammonium is less well understood. This study revealed the marine bacterium Phaeobacter inhibens DSM 17395, a Roseobacter group member, to have already depleted the external ammonium when only ~1/3 of the ultimately attained biomass is formed. This was paralleled by a three-fold increase in cellular nitrogen levels and rapid buildup of various nitrogen-containing intracellular metabolites (and enzymes for their biosynthesis) and biopolymers (DNA, RNA and proteins). Moreover, nitrogen-rich cells secreted potential RTX proteins and the antibiotic tropodithietic acid, perhaps to competitively secure pulses of external ammonium and to protect themselves from predation. This complex response may ensure growing cells and their descendants exclusive provision with internal nitrogen stocks. This nutritional strategy appears prevalent also in other roseobacters from distant geographical provenances and could provide a new perspective on the distribution of reduced nitrogen in marine environments, i.e. temporary accumulation in bacterioplankton cells
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