Diversity Of Ammonia-oxidizing Microorganisms In Natural And Engineered Ecosystems

Complete ammonia oxidizing bacteria(CAOB)have been recognized as a new member of ammonia-oxidizing microorganisms(AOMs)due to its single-step nitrification capability.However,the abundance and diversity of CAOB in environmental ecosystems were still far from known owing to the lack of specific molecular marker.Herein,a universal primer set specifically targeting both clades of CAOB amoA gene with high specificity and coverage was successfully designed.Intriguingly,real-time quantitative PCR tests revealed that CAOB were ubiquitous and unexpectedly abundant in agricultural soils,river sediments,intertidal zones,drinking water and wastewater treatment systems.Phylogenetic analysis indicated that clade A existed in all the five types of ecosystems,while clade B were only detected in soil and sediment samples.Four sub-clusters were further classified within clade A,in which N.nitrosa cluster dominated CAOB amoA in activated sludge samples while the new recognized soil cluster was the primary constitute in soils.CAOB also plays a non-negligible role in the ammonia oxidation process of domestic wastewater treatment plant(WWTP),but CAOB could not grow up in the environment of industrial sewage because wasterwater contains hardly degradable substances.Nitrosomonas accounts for more than 95%of the total AOB amoA gene sequences,of which the Nitrosospira oligotropha represents 29.54%of the total sequence number,indicating that it plays an important role in sewage treatment systems.Nitrososphaera and Nitrososphaera sister accounted for 78.87%of the total AO A amoA gene sequence,which can be inferred that they have a stronger advantage in WWTPs with higher ammonia nitrogen concentrations.Moreover,the niche specialization between different CAOB species and the environmental conditions were supposed to be the primary driven force to shape the diversity and community of CAOB.This study provided a strong evidence in support of the ubiquities and high abundances of CAOB in various environmental ecosystems and highlighted the significance of including CAOB as the new member of AOMs to re-evaluate the biogeochemical nitrogen cycle.