Importance of anaerobic ammonium oxidation as a nitrogen removal pathway in freshwater marsh sediments.

AIMS: To explore the role of anaerobic ammonium oxidation (anammox) in nitrogen removal in freshwater marshes. METHODS AND RESULTS: The 16S rRNA gene sequences of Candidatus Kuenenia and Candidatus Brocadia were simultaneously detected in the sediment of freshwater marshes of Green Bay Wetland that is located in Eastern China by using Illumina-based sequencing of the total bacterial 16S rRNA genes, and Candidatus Brocadia comprised more than 80% of the total anammox-related sequences. The abundance of anammox bacteria was determined by quantitative PCR on their hydrazine synthase (hzs) genes, which ranged from 3·13 × 104 to 1·58 × 105 copies per g sediment with little temporal variation. The potential anammox rates measured by 15 N-stable isotope pairing technique were 0·78-5·37 nmol N g-1 sediment per h, accounting for 4·3-38·5% of total sediment dinitrogen gas (N2 ) production. Both the anammox activity and its contribution to N2 production were sensitive to temporal variation and correlated well with the sediment NO3 - content. To further examine the nitrogen removal potential via anammox, batch culture was set-up to enrich anammox bacteria from the marsh sediments. Both the activity and abundance of anammox bacteria increased significantly after 6 months of incubation, varying from 61·6 to 95·8 nmol N g-1 sediment per h and 2·86 × 105 to 6·58 × 105 copies per g sediment respectively. CONCLUSIONS: Our results revealed the great potential of anammox in nitrogen removal in freshwater marshes. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study to show the anammox activity and its temporal variation in freshwater marsh sediments, which improved our understanding of nitrogen removal mechanisms in freshwater marshes.

Presence of diverse Candidatus Methylomirabilis oxyfera-like bacteria of NC10 phylum in agricultural soils.

AIMS: To better explore the distribution and diversity of Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria of NC10 phylum in soil environments. METHODS AND RESULTS: The vertical distribution and diversity of NC10 phylum bacteria were investigated in an agricultural field (surface layer, 0-10 cm; subsurface layer, 20-30 cm; deep layers, 50-60 and 90-100 cm) by using Illumina-based 16S rRNA (V3-V4 region) gene sequencing of soil DNA samples and quantitative PCR assays. It was found that the NC10-related reads accounted for 0·8-4·5% of the 16S rRNA pool in each examined core sample, with greater percentage being observed in deep soils than in surface soils and subsurface soils. The recovered NC10-related reads showed 85·1-96·9% identity to the 16S rRNA gene of M. oxyfera. A high diversity of NC10 phylum bacteria was observed in the examined soil cores. A total of 115 operational taxonomic units (OTU) were detected based on 3% sequence divergence in the recovered 16S rRNA genes. Phylogenetic analysis showed that four distinct groups of NC10 phylum bacteria (groups A, B, C and D) were present in the examined soil cores, with group B members being the dominant bacteria. The group A members, which are identified as the dominant bacteria responsible for anaerobic methane oxidation (AMO) coupled to nitrite reduction, can mainly be detected at 50-60 cm. Quantitative PCR further confirmed the presence of NC10 phylum bacteria, ranging from 3·8 × 10(6) to 9·3 × 10(6) copies g(-1) soil. CONCLUSIONS: The results showed the presence of diverse NC10 phylum bacteria in agricultural soils by using Illumina-based 16S rRNA gene sequencing and qPCR assays. SIGNIFICANCE AND IMPACT OF THE STUDY: The greatest level of diversity of NC10 phylum bacteria was reported to date in this study, which improved our understanding of the distribution of NC10 phylum bacterial communities in soil environments.