Ammonia-oxidizing bacteria and archaea in sediments of the Gulf of Mexico.

The diversity (richness and community composition) of ammonia-oxidizing archaea (AOA) and bacteria (AOB) within sediments of the Gulf of Mexico was examined. Using polymerase chain reaction primers designed to specifically target the archaeal ammonia monooxygenase-subunit (amoA) gene and bacterial amoA gene, we found AOA and AOB to be present in all three sampling sites. Archaeal amoA libraries were dominated by a few widely distributed Nitrosopumilus-like sequence types, whereas AOB diversity showed significant variation in both richness and community composition. Majority of the bacterial amoA sequences recovered belong to Betaproteobacteria and very few belong to Gammaproteobacteria. Results suggest that water depth and nutrient availability were identified as potential drivers that affected the selection of the AOA and AOB communities. Besides influencing the abundance of individual taxa, these environmental factors also had an impact on the overall richness of the overall AOA and AOB communities. The richness and diversity of AOA and AOB genes were higher at the shallowest sediments (100 m depth) and the deepest sediments (1300 m depth). The reduced diversity in the deepest sediments could be explained by much lower nutrient availability.