Unusual marine cyanobacteria/haptophyte symbiosis relies on N2fixation even in N-rich environments
Open Access
- 1 October 2020
- journal article
- research article
- Published by Oxford University Press (OUP) in The ISME Journal
- Vol. 14 (10), 2395-2406
- https://doi.org/10.1038/s41396-020-0691-6
Abstract
The microbial fixation of N(2)is the largest source of biologically available nitrogen (N) to the oceans. However, it is the most energetically expensive N-acquisition process and is believed inhibited when less energetically expensive forms, like dissolved inorganic N (DIN), are available. Curiously, the cosmopolitan N-2-fixing UCYN-A/haptophyte symbiosis grows in DIN-replete waters, but the sensitivity of their N(2)fixation to DIN is unknown. We used stable isotope incubations, catalyzed reporter deposition fluorescence in-situ hybridization (CARD-FISH), and nanoscale secondary ion mass spectrometry (nanoSIMS), to investigate the N source used by the haptophyte host and sensitivity of UCYN-A N(2)fixation in DIN-replete waters. We demonstrate that under our experimental conditions, the haptophyte hosts of two UCYN-A sublineages do not assimilate nitrate (NO3-) and meet little of their N demands via ammonium (NH4+) uptake. Instead the UCYN-A/haptophyte symbiosis relies on UCYN-A N(2)fixation to supply large portions of the haptophyte's N requirements, even under DIN-replete conditions. Furthermore, UCYN-A N(2)fixation rates, and haptophyte host carbon fixation rates, were at times stimulated by NO(3)(-)additions in N-limited waters suggesting a link between the activities of the bulk phytoplankton assemblage and the UCYN-A/haptophyte symbiosis. The results suggest N(2)fixation may be an evolutionarily viable strategy for diazotroph-eukaryote symbioses, even in N-rich coastal or high latitude waters.This publication has 74 references indexed in Scilit:
- Processes and patterns of oceanic nutrient limitationNature Geoscience, 2013
- Comparative Assessment of Nitrogen Fixation Methodologies, Conducted in the Oligotrophic North Pacific OceanApplied and Environmental Microbiology, 2012
- The sensitivity of marine N2 fixation to dissolved inorganic nitrogenFrontiers in Microbiology, 2012
- Direct and indirect costs of dinitrogen fixation in Crocosphaera watsonii WH8501 and possible implications for the nitrogen cycleFrontiers in Microbiology, 2012
- The organic complexation of iron in the marine environment: a reviewFrontiers in Microbiology, 2012
- Methodological Underestimation of Oceanic Nitrogen Fixation RatesPLOS ONE, 2010
- Metabolic streamlining in an open-ocean nitrogen-fixing cyanobacteriumNature, 2010
- Use of stable isotope‐labelled cells to identify active grazers of picocyanobacteria in ocean surface watersEnvironmental Microbiology, 2009
- Interannual variability of new production in the southern region of the California CurrentDeep Sea Research Part II: Topical Studies in Oceanography, 2003
- The use of amides and other organic nitrogen sources by the phytoplankton Emiliania huxleyiLimnology and Oceanography, 1997