Diversity, abundance and activity of ammonia-oxidizing microorganisms in fine particulate matter.

Increasing ammonia emissions could exacerbate air pollution caused by fine particulate matter (PM). Therefore, it is of great importance to investigate ammonia oxidation in PM. This study investigated the diversity, abundance and activity of ammonia oxidizing archaea (AOA), ammonia oxidizing bacteria (AOB) and complete ammonia oxidizers (Comammox) in PM collected in Beijing-Tianjin-Hebei megalopolis, China. Nitrosopumilus subcluster 5.2 was the most dominant AOA. Nitrosospira multiformis and Nitrosomonas aestuarii were the most dominant AOB. Comammox were present in the atmosphere, as revealed by the occurrence of Candidatus Nitrospira inopinata in PM. The average cell numbers of AOA, AOB and Ca. N. inopinata were 2.82 × 10, 4.65 × 10 and 1.15 × 10 cell m air, respectively. The average maximum nitrification rate of PM was 0.14 μg (NH-N) [m air·h]. AOA might account for most of the ammonia oxidation, followed by Comammox, while AOB were responsible for a small part of ammonia oxidation. Statistical analyses showed that Nitrososphaera subcluster 4.1 was positively correlated with organic carbon concentration, and Nitrosomonas eutropha showed positive correlation with ammonia concentration. Overall, this study expanded our knowledge concerning AOA, AOB and Comammox in PM and pointed towards an important role of AOA and Comammox in ammonia oxidation in PM.