Biogeochemical and metagenomic analysis of nitrite accumulation in the Gulf of Mexico hypoxic zone. (6th July 2015)

• Record Type: Journal Article
• Authors: Bristow, Laura A.; Sarode, Neha; Cartee, John; Caro‐Quintero, Alejandro; Thamdrup, Bo; Stewart, Frank J.
• Is Part Of: Limnology and oceanography. Volume 60:Number 5(2015:Sep.)
• Page Start: 1733
• Page End: 1750
• Publication Date: 2015-07-06
• Subjects: Limnology -- Periodicals; Oceanography -- Periodicals; Océanographie; Limnologie; Limnology; Oceanography; Computer network resources; Périodique électronique (Descripteur de forme); Ressource Internet (Descripteur de forme); Periodicals; 551.4805
• DOI: 10.1002/lno.10130
• Languages: English
• ISSNs: 0024-3590

Abstract

Abstract: The Louisiana Shelf in the Gulf of Mexico experiences recurrent bottom water hypoxia under summertime eutrophic conditions. The onset, maintenance, and breakdown of hypoxia are associated with dynamic microbial biogeochemical cycles. However, the distribution of microbial taxa and metabolisms across Shelf oxygen gradients remains under‐characterized. We combined biogeochemical analyses of nitrogen (N) distributions and metabolic rates with metagenomic and metatranscriptomic analysis of summertime Shelf waters. Samples from an east–west transect during July 2012 revealed an inverse relationship between nitrite and oxygen concentrations, with concentrations exceeding 1 μmol L −1 at ∼ 50% oxygen saturation and reaching 4.6 μmol L −1 at the most oxygen‐depleted sites. Historical data confirms that nitrite accumulation occurs frequently in this region both above and below the hypoxic threshold. Experimental incubations demonstrated a strong decoupling between the two steps of nitrification, with ammonia oxidation proceeding up to 30 times faster than nitrite oxidation under low oxygen. 16S rRNA gene, metagenome, and metatranscriptome sequencing revealed a diverse microbial community, stratified over shallow (< 10 m) depth gradients, with an enrichment of ammonia‐oxidizing Thaumarchaeota genes and transcripts in deeper more oxygen‐depleted layers, and a comparatively low representation of sequences related to nitrite oxidation. A range of factors, including temperature and substrate availability, which may be linked indirectly to bottom water oxygen content, potentially drives decoupling of ammonia and nitrite oxidation on the Louisiana Shelf. Nitrite accumulation in hypoxic zones remains understudied and may have important effects on microbial nitrogen flux, algal dynamics, and production.