The Braarudosphaera bigelowii genome reveals cellular remodeling around a nitrogen-fixing organelle

A 472.1-Mb genome of Braarudosphaera bigelowii FR-21 reveals extensive nitrogen-metabolism remodeling linked to its UCYN-A nitroplast association.

• Why it matters: Without a reference genome, it has been hard to identify genomic features that accompany the host’s nitrogen-fixing organelle and to test whether this lifestyle reflects unusual evolutionary placement.
• What they did: They assembled nuclear and organellar resources for FR-21 (472.1 Mb nuclear; 1.49 Mb nitroplast, 107 kb chloroplast, 44 kb mitochondrial) and annotated repeats (~77% repetitive; ~108 Mb nonrepetitive; ~16,000 protein-coding genes).
• The result: The host lacks major nitrate/nitrite assimilation components and shows reduced use of urea, cyanate, and several recycled nitrogen sources, while retaining ammonium transport and the glutamine synthetase–glutamate synthase pathway; it also expands flavodoxin and cryptochrome candidates with nitroplast-targeting motifs.

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