Non-cyanobacterial diazotrophs: global diversity, distribution, ecophysiology, and activity in marine waters.

Biological dinitrogen (N2) fixation supplies nitrogen to the oceans, supporting primary productivity, and is carried out by some bacteria and archaea referred to as diazotrophs. Cyanobacteria are conventionally considered to be the major contributors to marine N2 fixation, but non-cyanobacterial diazotrophs (NCDs) have been shown to be distributed throughout ocean ecosystems. However, the biogeochemical significance of marine NCDs has not been demonstrated.

Empirical relationship between nifH gene abundance and diazotroph cell concentration in the North Pacific Subtropical Gyre.

Cyanobacterial N -fixing microorganisms (diazotrophs) play a critical role in nitrogen and carbon cycling in the oceans; hence, accurate measurements of diazotroph abundance are imperative for understanding ocean biogeochemistry. Marine diazotroph abundances are often assessed using qPCR of the nifH gene, a sensitive, taxa-specific, and time/cost-efficient method. However, the validity of nifH abundance as a proxy for cell concentration has recently been questioned.

Light and depth dependency of nitrogen fixation by the non-photosynthetic, symbiotic cyanobacterium UCYN-A.

The symbiotic cyanobacterium UCYN-A is one of the most globally abundant marine dinitrogen (N )-fixers, but cultures have not been available and its biology and ecology are poorly understood. We used cultivation-independent approaches to investigate how UCYN-A single-cell N fixation rates (NFRs) and nifH gene expression vary as a function of depth and photoperiod. Twelve-hour day/night incubations showed that UCYN-A only fixed N during the day.

Environmental Controls of Oyster-Pathogenic Vibrio spp. in Oregon Estuaries and a Shellfish Hatchery.

spp. have been a persistent concern for coastal bivalve hatcheries, which are vulnerable to environmental pathogens in the seawater used for rearing larvae, yet the biogeochemical drivers of oyster-pathogenic spp. in their planktonic state are poorly understood.

Corrigendum: Microbiome of Colonies from the North Pacific Subtropical Gyre.

[This corrects the article on p. 1122 in vol. 8, PMID: 28729854.

Microbiome of Colonies from the North Pacific Subtropical Gyre.

Filamentous diazotrophic Cyanobacteria of the genus , often found in colonial form, provide an important source of new nitrogen to tropical and subtropical marine ecosystems. Colonies are composed of several clades of in association with a diverse community of bacterial and eukaryotic epibionts. We used high-throughput 16S rRNA and gene sequencing, carbon (C) and dinitrogen (N) fixation assays, and metagenomics to describe the diversity and functional potential of the microbiome associated with colonies collected from the North Pacific Subtropical Gyre (NPSG).

Physiological response of Crocosphaera watsonii to enhanced and fluctuating carbon dioxide conditions.

We investigated the effects of elevated pCO2 on cultures of the unicellular N2-fixing cyanobacterium Crocosphaera watsonii WH8501. Using CO2-enriched air, cultures grown in batch mode under high light intensity were exposed to initial conditions approximating current atmospheric CO2 concentrations (∼ 400 ppm) as well as CO2 levels corresponding to low- and high-end predictions for the year 2100 (∼ 750 and 1000 ppm). Following acclimation to CO2 levels, the concentrations of particulate carbon (PC), particulate nitrogen (PN), and cells were measured over the diurnal cycle for a six-day period spanning exponential and early stationary growth phases.