In marine oxygen minimum zones (OMZs), ammonia-oxidizing archaea (AOA) rather than marine ammonia-oxidizing bacteria (AOB) may provide nitrite to anaerobic ammonium-oxidizing (anammox) bacteria. Here we demonstrate the cooperation between marine anammox bacteria and nitrifiers in a laboratory-scale model system under oxygen limitation. A bioreactor containing ‘Candidatus Scalindua profunda’ marine anammox bacteria was supplemented with AOA (Nitrosopumilus maritimus strain SCM1) cells and limited amounts of oxygen. In this way a stable mixed culture of AOA, and anammox bacteria was established within 200 days while also a substantial amount of endogenous AOB were enriched. ‘Ca. Scalindua profunda’ and putative AOB and AOA morphologies were visualized by transmission electron microscopy and a C18 anammox [3]-ladderane fatty acid was highly abundant in the oxygen-limited culture. The rapid oxygen consumption by AOA and AOB ensured that anammox activity was not affected. High expression of AOA, AOB and anammox genes encoding for ammonium transport proteins was observed, likely caused by the increased competition for ammonium. The competition between AOA and AOB was found to be strongly related to the residual ammonium concentration based on amoA gene copy numbers. The abundance of archaeal amoA copy numbers increased markedly when the ammonium concentration was below 30 μM finally resulting in almost equal abundance of AOA and AOB amoA copy numbers. Massive parallel sequencing of mRNA and activity analyses further corroborated equal abundance of AOA and AOB. PTIO addition, inhibiting AOA activity, was employed to determine the relative contribution of AOB versus AOA to ammonium oxidation. The present study provides the first direct evidence for cooperation of archaeal ammonia oxidation with anammox bacteria by provision of nitrite and consumption of oxygen.

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Interfacial materials play a vital role in determining the charge carrier collection for the performance of polymer solar cells (PSCs). Herein, a monomolecular (3‐aminopropyl) triethoxysilane (APTES) layer is deposited onto ZnO, acting as cathode interfacial layer (CIL) in the inverted PSCs. Inverted PBDB‐T:IT‐M PSCs with the ZnO‐APTES CILs exhibit a power conversion efficiency of 11.53% with a short‐circuit current density of 18.37 mA cm−2, an open‐circuit voltage of 0.91 V and fill factor of 68.77%. More than 13% improvement on the power conversion efficiency is achieved by inserting APTES, due to efficient charge collection obtained by a built‐in electric field and reduced oxygen defects at the ZnO surface. The results indicate that the ZnO‐APTES layer is an efficient CIL for inverted PSCs.