AME prepress abstract  -  doi: 10.3354/ame01817

Aerobic and anaerobic ammonium oxidizers in the Cariaco Basin: distributions of major taxa and nitrogen species across the redoxcline

Sara Cernadas-Martín*, Elizabeth A. Suter, Mary I. Scranton, Yrene Astor, Gordon T. Taylor

*Email: sara.cernadas@stonybrook.edu.

ABSTRACT: Depth distributions of cells and functional gene copies from anaerobic ammonium-oxidizing (anammox) bacteria, aerobic ammonium-oxidizing bacteria (AOB) and archaea (AOA) in the Cariaco Basin were obtained using FISH and q-PCR assays. These distributions were compared to concentrations of dissolved ammonium (NH4+), nitrite (NO2-), nitrate (NO3-), hydrogen sulfide (H2S) and oxygen (O2) along the redoxcline during three cruises. Cell counts of anammox bacteria and copies of their nitrite reductase gene (Scalindua-nirS), were consistently observed in two distinct layers: the suboxic zone (< 1.1 x 106 cells L-1) and the upper euxinic zone (< 4.7 x 106 cells L-1). We hypothesize that anammox bacteria vertically organize in response to NO2- sources, with NO2- for the shallower assemblage supplied by nitrification and for the deeper assemblage by denitrification. Peaks in AOA cell abundances (up to 14.8 x106 cells L-1) consistently coincided with copy numbers of archaeal ammonia monooxygenase subunit A gene (Archaeal amoA) in the lower oxic zone. Peak abundances of β- and γ-proteobacterial AOB cells (up to 24.0 x 106 cells L-1) and one of their ammonia monooxygenase genes (β-amoA) overlapped above the shallow anammox peak. Our results suggest that anammox bacteria, AOB, AOA and denitrifiers are metabolically interdependent and ultimately controlled by vertical fluxes of O2, NO3-, NO2-, and NH4+ in the Cariaco Basin.