Distinct ecological niches of marine symbiotic N₂‐fixing cyanobacterium Candidatus Atelocyanobacterium thalassa sublineages

Abstract

1 1 2 3 4 5 6 7 8 A recently described symbiosis between the metabolically streamlined nitrogen-fixing cyanobacterium UCYN-A and a single-celled eukaryote prymnesiophyte alga is widely distributed throughout tropical and subtropical marine waters, and is thought to contribute significantly to nitrogen fixation in these regions. Several UCYN-A sublineages have been defined based on UCYN-A nitrogenase (nifH) sequences. Due to the low abundances of UCYN-A in the global oceans, currently existing molecular techniques are limited for detecting and quantifying these organisms. A targeted approach is needed to adequately characterize the diversity of this important marine cyanobacterium, and to advance understanding of its ecological importance. We present findings on the distribution of UCYN-A sublineages based on high throughput sequencing of UCYN-A nifH PCR amplicons from 78 samples distributed throughout many major oceanic provinces. These UCYN-A nifH fragments were used to define oligotypes, alternative taxonomic units defined by nucleotide positions with high variability. The dataset was dominated by a single oligotype associated with the UCYN-A1 sublineage, consistent with previous observations of relatively high abundances in tropical and subtropical regions. However, this analysis also revealed for the first time the widespread distribution of the UCYN-A3 sublineage in oligotrophic waters. Furthermore, distinct assemblages of UCYN-A oligotypes were found in oligotrophic and coastally-influenced waters. This unique dataset provides a framework for determining the environmental controls on UCYN-A distributions and the ecological importance of the different sublineages.

Biological N2 Fixation in the Upwelling Region off NW Iberia: Magnitude, Relevance, and Players

“…The higher UCYN-A2 abundance is consistent with recent findings pointing out this sublineage, although globally distributed (Cabello et al, 2015;Martínez-Pérez et al, 2016), mainly inhabit coastal regions, whereas UCYN-A1 dominates in the oligotrophic open ocean (Thompson et al, 2014;Messer et al, 2015;Turk-Kubo et al, 2017). The UCYN-A abundances detected were in the mediumlow range of global abundances reported by Luo et al (2012), Martínez-Pérez et al (2016), and Benavides and Voss (2015) in the North Atlantic.…”

“…Six different UCYN-A sublineages (UCYN-A1, -A2, -A3, -A4, -A5, -A6) have been defined based on the genetic diversity of the nifH sequences available in GenBank (Thompson et al, 2014;Farnelid et al, 2016;Turk-Kubo et al, 2017). The Gammaproteobacteriaaffiliated phylotype γ-24774A11 (also named Gamma A or UMB) also exhibits a wide distribution, including contrasting marine environments in the Atlantic, Pacific and Indian Oceans (e.g., Church et al, 2005;Moisander et al, 2008;Langlois et al, 2015;Benavides et al, 2016).…”

UCYN‐A3, a newly characterized open ocean sublineage of the symbiotic N2‐fixing cyanobacterium Candidatus Atelocyanobacterium thalassa

“…However, our findings suggest that the sublineage detected at Station ALOHA was in fact UCYN‐A3, not UCYN‐A2. First, UCYN‐A3 nifH amplicon sequences were present at relative abundances of approximately 10% at Station ALOHA, while UCYN‐A2 sequences were virtually absent, which is consistent with a recent report of UCYN‐A3 in the NPSG (including Station ALOHA) by Turk‐Kubo and colleagues (). Second, the UCYN‐A2 qPCR assay cannot be used to distinguish between UCYN‐A2 and UCYN‐A3, as it does not contain sufficient mismatches to prevent cross‐hybridization with UCYN‐A3 (and UCYN‐A4) sublineages (Farnelid et al ., ).…”

“…UCYN‐A specific nifH gene amplification and sequencing using Illumina MiSeq Turk‐Kubo and colleagues ().…”

A Short Comparison of Two Marine Planktonic Diazotrophic Symbioses Highlights an Un-quantified Disparity

“…The het-3 symbiont of Chaetoceros compressus was isolated into culture, genome sequenced (CalSC01) and has been maintained asymbiotic since 2004 Hilton et al, 2013). Currently there are six nifH clades designated as UCYN-A (UCYNA-1 through UCYN-A6), two clades are derived from symbiotic cells (i.e., UCYN-A1, UCYN-A2) (Thompson et al, 2014;Farnelid et al, 2016;Turk-kubo et al, 2017) and no UCYN-A cells have been isolated into culture.…”