Academic Report on Jun.24

Report Topic:Nitrite-dependent Oxidation of Ammonium: A New Biochemical Process in the Nitrogen Cycle  

Reporter: Prof. Ji-Dong Gu, The University of Hong Kong

Time: 14:30, Jun. 24, 2017

Location: Academic Hall of State Key Laboratory


Nitrogen is fundamental to evolution of life and ecosystem function. Bacteria responsible for nitrite-dependent oxidation of ammonium (n-doa) were first discovered in the late 1990s and then were confirmed to contribute to 30-50% of the N2 produced in ocean ecosystems and also some wastewater treatment plants where n-doa bacteria were active. This group of bacteria can be detected with applications of biochemical and molecular markers for their diversity and abundance in different ecosystems. In this talk, I will start with a brief history on the discovery of this bacterium, and its molecular detection methods available currently and their distribution pattern in different ecosystems. All available molecular biomarkers including 16S rRNA gene and biochemical based ones including nirS, hzs, hzo and others will be presented for their specificity and efficiency in recovering this group of bacteria from a wide range of samples from Pearl River sediment, mangrove, pristine wetland and polluted ones, rice paddy to shallow and deep ocean sediments of the South China Sea (SCS). Based on phylogenetic analyses, deduced protein sequences of the enzymes involved in n-doa were grouped into relevant known clusters and new ones with lower similarity to the known sequences were confirmed from SCS. These new clusters within Ca. Scalindua species were named to honor the Chinese oceanographer Zheng He (1371–1433) as Ca. Scalindua zhenghei I, II, and III indigenous to the SCS. We also discover a clear pattern on the distribution of different n-doa bacterial genera and species along a gradient from pristine clean to anthropogenic impacted environments. Our results collectively showed that n-doa bacteria are highly niche-specific within the different ecosystems with anthropogenic influence as the key factor.