Genomic deletions disrupt nitrogen metabolism pathways of a cyanobacterial diatom symbiont

Diatoms with symbiotic N 2 -fixing cyanobacteria are often abundant in the oligotrophic open ocean gyres. The most abundant cyanobacterial symbionts form heterocysts (specialized cells for N 2 fixation) and provide nitrogen (N) to their hosts, but their morphology, cellular locations and abundances...

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Bibliographic Details
Published in:Nature communications 2013-04, Vol.4 (1), p.1767
Main Authors: Hilton, Jason A., Foster, Rachel A., James Tripp, H., Carter, Brandon J., Zehr, Jonathan P., Villareal, Tracy A.
Format: Article
Language:English
Subjects:
631/208/212/2304
631/326/41/547
Cyanobacteria - genetics
Diatoms - microbiology
Flow Cytometry
Genes, Bacterial - genetics
Genome, Bacterial - genetics
Humanities and Social Sciences
Metabolic Networks and Pathways - genetics
multidisciplinary
Nitrogen - metabolism
Nitrogenase - genetics
Operon - genetics
Phylogeny
Science
Science (multidisciplinary)
Sequence Deletion - genetics
Symbiosis - genetics
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Summary:Diatoms with symbiotic N 2 -fixing cyanobacteria are often abundant in the oligotrophic open ocean gyres. The most abundant cyanobacterial symbionts form heterocysts (specialized cells for N 2 fixation) and provide nitrogen (N) to their hosts, but their morphology, cellular locations and abundances differ depending on the host. Here we show that the location of the symbiont and its dependency on the host are linked to the evolution of the symbiont genome. The genome of Richelia (found inside the siliceous frustule of Hemiaulus ) is reduced and lacks ammonium transporters, nitrate/nitrite reductases and glutamine:2-oxoglutarate aminotransferase. In contrast, the genome of the closely related Calothrix (found outside the frustule of Chaetoceros ) is more similar to those of free-living heterocyst-forming cyanobacteria. The genome of Richelia is an example of metabolic streamlining that has implications for the evolution of N 2 -fixing symbiosis and potentially for manipulating plant–cyanobacterial interactions. Cyanobacterial symbionts of marine diatoms can localize intracellularly or externally to their host partners. Here Hilton et al . describe the genomes of two diazotroph cyanobacterial symbionts of diatoms and show that the location of the symbiont affects expression of nitrogen assimilation genes.
ISSN:2041-1723
DOI:10.1038/ncomms2748