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https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

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Summary  Sediments across the  N amibian continental margin feature a strong microbial activity gradient at their surface. This is reflected in ammonium concentrations of < 10 μM in oligotrophic abyssal plain sediments near the  S outh  A tlantic  G yre compared with ammonium concentrations of > 700 μM in upwelling areas near the coast. Here we address changes in apparent abundance and structure of ammonia‐oxidizing archaeal and bacterial communities ( AOA  and  AOB ) along a transect of seven sediment stations across the  N amibian shelf by analysing their respective ammonia monooxygenase genes (  amoA  ). The relative abundance of archaeal and bacterial   amoA   (g −1   DNA ) decreased with increasing ammonium concentrations, and bacterial   amoA   frequently outnumbered archaeal   amoA   at the sediment–water interface [0–1 cm below seafloor (cmbsf)]. In contrast,  AOA  were apparently as abundant as  AOB  or dominated in several deeper (> 10 cmbsf), anoxic sediment layers. Phylogenetic analyses showed a change within the  AOA  community along the transect, from two clusters without cultured representatives at the gyre to   N   itrososphaera  and   N   itrosopumilus  clusters in the upwelling region.  AOB  almost exclusively belonged to the   N   itrosospira  cluster 1. Our results suggest that this predominantly marine  AOB  lineage without cultured representatives can thrive at low ammonium concentrations and is active in the marine nitrogen cycle.

environmental microbiology reports

Ammonia‐oxidizing  B acteria of the   N   itrosospira  cluster 1 dominate over ammonia‐oxidizing  A rchaea in oligotrophic surface sediments near the  S outh  A tlantic  G yre