Nitrogen uptake rates and phytoplankton composition across contrasting North Atlantic Ocean coastal regimes north and south of Cape Hatteras.

Understanding nitrogen (N) uptake rates respect to nutrient availability and the biogeography of phytoplankton communities is crucial for untangling the complexities of marine ecosystems and the physical, biological, and chemical forces shaping them. In the summer of 2016, we conducted measurements of bulk microbial uptake rates for six N-labeled substrates: nitrate, nitrite, ammonium, urea, cyanate, and dissolve free amino acids across distinct marine provinces, including the continental shelf of the Mid-and South Atlantic Bights (MAB and SAB), the Slope Sea, and the Gulf Stream, marking the first instance of simultaneously measuring six different N uptake rates in this dynamic region. Total measured N uptake rates were lowest in the Gulf Stream followed by the SAB.

Quantification of Amine- and Alcohol-Containing Metabolites in Saline Samples Using Pre-extraction Benzoyl Chloride Derivatization and Ultrahigh Performance Liquid Chromatography Tandem Mass Spectrometry (UHPLC MS/MS).

Dissolved metabolites serve as nutrition, energy, and chemical signals for microbial systems. However, the full scope and magnitude of these processes in marine systems are unknown, largely due to insufficient methods, including poor extraction of small, polar compounds using common solid-phase extraction resins. Here, we utilized pre-extraction derivatization and ultrahigh performance liquid chromatography electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS) to detect and quantify targeted dissolved metabolites in seawater and saline culture media.

Potential virus-mediated nitrogen cycling in oxygen-depleted oceanic waters.

Viruses play an important role in the ecology and biogeochemistry of marine ecosystems. Beyond mortality and gene transfer, viruses can reprogram microbial metabolism during infection by expressing auxiliary metabolic genes (AMGs) involved in photosynthesis, central carbon metabolism, and nutrient cycling. While previous studies have focused on AMG diversity in the sunlit and dark ocean, less is known about the role of viruses in shaping metabolic networks along redox gradients associated with marine oxygen minimum zones (OMZs).

Resource partitioning of phytoplankton metabolites that support bacterial heterotrophy.

The communities of bacteria that assemble around marine microphytoplankton are predictably dominated by Rhodobacterales, Flavobacteriales, and families within the Gammaproteobacteria. Yet whether this consistent ecological pattern reflects the result of resource-based niche partitioning or resource competition requires better knowledge of the metabolites linking microbial autotrophs and heterotrophs in the surface ocean. We characterized molecules targeted for uptake by three heterotrophic bacteria individually co-cultured with a marine diatom using two strategies that vetted the exometabolite pool for biological relevance by means of bacterial activity assays: expression of diagnostic genes and net drawdown of exometabolites, the latter detected with mass spectrometry and nuclear magnetic resonance using novel sample preparation approaches.

Cyanobacteria and cyanophage contributions to carbon and nitrogen cycling in an oligotrophic oxygen-deficient zone.

Up to half of marine N losses occur in oxygen-deficient zones (ODZs). Organic matter flux from productive surface waters is considered a primary control on N production. Here we investigate the offshore Eastern Tropical North Pacific (ETNP) where a secondary chlorophyll a maximum resides within the ODZ.

Utilization of urea and cyanate in waters overlying and within the eastern tropical north Pacific oxygen deficient zone.

In marine oxygen deficient zones (ODZs), which contribute up to half of marine N loss, microbes use nitrogen (N) for assimilatory and dissimilatory processes. Here, we examine N utilization above and within the ODZ of the Eastern Tropical North Pacific Ocean, focusing on distribution, uptake and genes for the utilization of two simple organic N compounds, urea and cyanate. Ammonium, urea and cyanate concentrations generally peaked in the oxycline while uptake rates were highest in the surface.

Biological nitrogen fixation in the oxygen-minimum region of the eastern tropical North Pacific ocean.

Biological nitrogen fixation (BNF) was investigated above and within the oxygen-depleted waters of the oxygen-minimum zone of the Eastern Tropical North Pacific Ocean. BNF rates were estimated using an isotope tracer method that overcame the uncertainty of the conventional bubble method by directly measuring the tracer enrichment during the incubations. Highest rates of BNF (~4 nM day) occurred in coastal surface waters and lowest detectable rates (~0.

Chromatographic determination of nanomolar cyanate concentrations in estuarine and sea waters by precolumn fluorescence derivatization.

Recent studies suggest that cyanate (OCN(-)) is a potentially important source of reduced nitrogen (N) available to support the growth of aquatic microbes and, thus, may play a role in aquatic N cycling. However, aquatic OCN(-) distributions have not been previously described because of the lack of a suitable assay for measuring OCN(-) concentrations in natural waters. Previous methods were designed to quantify OCN(-) in aqueous samples with much higher reduced N concentrations (micromolar levels) than those likely to be found in natural waters (nanomolar levels).

Draft genome sequence of strain HIMB100, a cultured representative of the SAR116 clade of marine Alphaproteobacteria.

Strain HIMB100 is a planktonic marine bacterium in the class Alphaproteobacteria. This strain is of interest because it is one of the first known isolates from a globally ubiquitous clade of marine bacteria known as SAR116 within the family Rhodospirillaceae. Here we describe preliminary features of the organism, together with the draft genome sequence and annotation.