| Description |
The global nitrogen cycle was essentially considered 'linear' as it is straightforward from the atmosphere and back again. However, discoveries of additional pathways suggested that there is still much to be learned about the nitrogen cycling, the organisms responsible, and their interactions in natural and anthropogenic ecosystems. In this research two novel innovative nitrogen transformation pathways - (a) nitrite-dependent denitrification coupled with anaerobic methane oxidation (n-DAMO) and (b) anaerobic ammonium oxidation (Anammox) - investigated to unravel the diversity and contributions of micro-organisms. The roles of aerobic (AOM) and anaerobic methane-oxidizing (n-DAMO) organisms coupled with denitrification were evaluated in (a) wetlands and (b) riverine sediments. AOM coupled with denitrification (nitrate-dependent) contributed to 9.8-7.3 and 4.5-3.5% oxidation of methane produced in wetlands and riverine ecosystems, respectively. Contributions of the n-DAMO process were also estimated, and it was more prominent in riverine sediments. Subsequently, riverine sediments were investigated for the microbial diversity using 'omics'. A laboratory-scale reactor enriched n-DAMO prokaryotes from riverine sediments. 'Omics' data and anaerobic methane oxidation rates confirmed plausible enrichment of n-DAMO prokaryotes. The plausibility to use n-DAMO prokaryotes for engineered ecosystems was investigated. After 19 months of n-DAMO reactor operation, nitrite removal rate of 2.88mmol L-1 d-1 was achieved. The increased enrichment was evident from higher 16SrRNA gene copy numbers and CH4 oxidation rates coupled with NO2- -N removal (21μM to 190μM of CH4 d-1). Novel primers targeting the unique nitric oxide dismutase (nod) gene were developed and tested. Phylogenetic analysis revealed that enriched n-DAMO organisms related to the Ca' Methylomirabilis oxyfera. The complex community existing in Anammox bioreactors were examined in two laboratory-scale reactors: (a) suspended (SGR) and (b) attached (AGR) growth. In a period of 220 days, both bioreactors achieved comparable rates in total inorganic nitrogen (TIN) removal of 88±4% and 86±2%. The investigation of the community-structure using 'omics' revealed Anammox sp. was related to Ca' B. sinica sp. with the dominant flanking community comprising of Anaerolinea, Ignavibacterium, and Rhodocyclaceae sp. Genome analysis of Anammox bacterial sp. extracted from SGR and AGR metagenome revealed species could be placed under genera Ca' Brocardia, expanding Anammox diversity. |
