Response of the ubiquitous pelagic diatom Thalassiosira weissflogii to darkness and anoxia.

Anja Kamp,Peter Stief,Jan Knappe,Dirk De Beer,Adrianna Ianora

doi:10.1371/journal.pone.0082605

Abstract

Thalassiosira weissflogii, an abundant, nitrate-storing, bloom-forming diatom in the world’s oceans, can use its intracellular nitrate pool for dissimilatory nitrate reduction to ammonium (DNRA) after sudden shifts to darkness and anoxia, most likely as a survival mechanism. T. weissflogii cells that stored 4 mM 15N-nitrate consumed 1.15 (±0.25) fmol NO3 - cell-1 h-1 and simultaneously produced 1.57 (±0.21) fmol 15NH4 + cell-1 h-1 during the first 2 hours of dark/anoxic conditions. Ammonium produced from intracellular nitrate was excreted by the cells, indicating a dissimilatory rather than assimilatory pathway. Nitrite and the greenhouse gas nitrous oxide were produced at rates 2-3 orders of magnitude lower than the ammonium production rate. While DNRA activity was restricted to the first few hours of darkness and anoxia, the subsequent degradation of photopigments took weeks to months, supporting the earlier finding that diatoms resume photosynthesis even after extended exposure to darkness and anoxia. Considering the high global abundance of T. weissflogii, its production of ammonium and nitrous oxide might be of ecological importance for oceanic oxygen minimum zones and the atmosphere, respectively.

Highlights

Diatoms are a key group of the eukaryotic phytoplankton of the world’s oceans from polar to tropical latitudes
The study revealed that A. coffeaeformis stored NO3- intracellularly and used it for Dissimilatory Nitrate Reduction to Ammonium (DNRA; NO3NO2- NH4+) after sudden exposure to darkness and anoxia
We further investigated the stability of photopigments after exposure to darkness and anoxia as an indicator of the dark survival potential of T. weissflogii

Summary

Introduction

Diatoms are a key group of the eukaryotic phytoplankton of the world’s oceans from polar to tropical latitudes. This study addresses the response of the pelagic, NO3--storing diatom Thalassiosira weissflogii to darkness and anoxia with respect to dissimilatory NO3- reduction and stability of photopigments. The time courses of intracellular NO3- concentrations in T. weissflogii, and NO3- and NH4+ concentrations in the growth medium under dark/anoxic versus light/oxic conditions were followed in a non-labeling experiment and a 15N-stable isotope labeling experiment (see below).

Results

Conclusion