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Title: Open ocean and coastal strains of the N2-fixing cyanobacterium UCYN-A have distinct transcriptomes

Decades of research on marine N2fixation focused onTrichodesmium, which are generally free-living cyanobacteria, but in recent years the endosymbiotic cyanobacteriumCandidatusAtelocyanobacterium thalassa (UCYN-A) has received increasing attention. However, few studies have shed light on the influence of the host versus the habitat on UCYN-A N2fixation and overall metabolism. Here we compared transcriptomes from natural populations of UCYN-A from oligotrophic open-ocean versus nutrient-rich coastal waters, using a microarray that targets the full genomes of UCYN-A1 and UCYN-A2 and known genes for UCYN-A3. We found that UCYN-A2, usually regarded as adapted to coastal environments, was transcriptionally very active in the open ocean and appeared to be less impacted by habitat change than UCYN-A1. Moreover, for genes with 24 h periodic expression we observed strong but inverse correlations among UCYN-A1, A2, and A3 to oxygen and chlorophyll, which suggests distinct host-symbiont relationships. Across habitats and sublineages, genes for N2fixation and energy production had high transcript levels, and, intriguingly, were among the minority of genes that kept the same schedule of diel expression. This might indicate different regulatory mechanisms for genes that are critical to the symbiosis for the exchange of nitrogen for carbon from the host. Our results underscore the importance of N2fixation in UCYN-A symbioses across habitats, with consequences for community interactions and global biogeochemical cycles.

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Award ID(s):
2241005
PAR ID:
10518146
Author(s) / Creator(s):
; ;
Editor(s):
Kothe, Erika
Publisher / Repository:
PLOS ONE
Date Published:
Journal Name:
PLOS ONE
Volume:
18
Issue:
5
ISSN:
1932-6203
Page Range / eLocation ID:
e0272674
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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