19 research outputs found
Down under the tunic: bacterial biodiversity hotspots and widespread ammonia-oxidizing archaea in coral reef ascidians
14 páginas, 3 tablas, 3 figuras.Ascidians are ecologically important components of marine ecosystems yet the ascidian microbiota
remains largely unexplored beyond a few model species. We used 16S rRNA gene tag
pyrosequencing to provide a comprehensive characterization of microbial symbionts in the tunic
of 42 Great Barrier Reef ascidian samples representing 25 species. Results revealed high bacterial
biodiversity (3 217 unique operational taxonomic units (OTU0.03) from 19 described and 14 candidate
phyla) and the widespread occurrence of ammonia-oxidizing Thaumarchaeota in coral reef ascidians
(24 of 25 host species). The ascidian microbiota was clearly differentiated from seawater microbial
communities and included symbiont lineages shared with other invertebrate hosts as well
as unique, ascidian-specific phylotypes. Several rare seawater microbes were markedly enriched
(200–700 fold) in the ascidian tunic, suggesting that the rare biosphere of seawater may act as a
conduit for horizontal symbiont transfer. However, most OTUs (71%) were rare and specific to single
hosts and a significant correlation between host relatedness and symbiont community similarity
was detected, indicating a high degree of host-specificity and potential role of vertical transmission
in structuring these communities. We hypothesize that the complex ascidian microbiota revealed
herein is maintained by the dynamic microenvironments within the ascidian tunic, offering optimal
conditions for different metabolic pathways such as ample chemical substrate (ammonia-rich host
waste) and physical habitat (high oxygen, low irradiance) for nitrification. Thus, ascidian hosts
provide unique and fertile niches for diverse microorganisms and may represent an important and
previously unrecognized habitat for nitrite/nitrate regeneration in coral reef ecosystems.This research was funded by the Marie Curie International
Reintegration Grant FP7-PEOPLE-2010-RG 277038 (within
the 7th European Community Framework Program),
the Spanish Government projects CTM2010-17755 and
CTM2010-22218 and the Catalan Government grant 2009
SGR-484 for Consolidated Research Groups. NSW was
funded through an Australian Research Council Future
Fellowship (FT1200100480).Peer reviewe
Ecological control of nitrite in the upper ocean
Microorganisms oxidize organic nitrogen to nitrate in a series of steps. Nitrite, an intermediate product, accumulates at the base of the sunlit layer in the subtropical ocean, forming a primary nitrite maximum, but can accumulate throughout the sunlit layer at higher latitudes. We model nitrifying chemoautotrophs in a marine ecosystem and demonstrate that microbial community interactions can explain the nitrite distributions. Our theoretical framework proposes that nitrite can accumulate to a higher concentration than ammonium because of differences in underlying redox chemistry and cell size between ammonia- and nitrite-oxidizing chemoautotrophs. Using ocean circulation models, we demonstrate that nitrifying microorganisms are excluded in the sunlit layer when phytoplankton are nitrogen-limited, but thrive at depth when phytoplankton become light-limited, resulting in nitrite accumulation there. However, nitrifying microorganisms may coexist in the sunlit layer when phytoplankton are iron- or light-limited (often in higher latitudes). These results improve understanding of the controls on nitrification, and provide a framework for representing chemoautotrophs and their biogeochemical effects in ocean models.Simons Foundation (Award 329108)Gordon and Betty Moore Foundation (Grant GBMF3778)National Science Foundation (U.S.) (Grant OCE-1315201)National Science Foundation (U.S.) (Grant OCE-1558702)National Science Foundation (U.S.) (Grant 1434007