INT-02 New understanding of marine nitrogen cycle: from microbes to the global ocean
 
 
 
Poster
Highly diverse and active diazotrophs and their potential adaptive mechanisms in a shallow submarine hydrothermal system
Tuesday 10th @ 1610-1730 , Conference Room 5
S-INT-02-01
Wednesday 11th @ 1610-1750 Exhibition Hall
Mingming Chen* , State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Science, Xiamen University, Xiamen, 361102, China
Yufang Li, Fisheries College, Jimei University, Xiamen 361021, China
Kai Tang, State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Science, Xiamen University, Xiamen, 361102, China
Anyi Hu, CAS Key Laboratory of Urban pollutant Conversion & Fujian Key Laboratory of Watershed Ecology, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China University of Chinese Academy of Sciences, Beijing 100049, China
Wei Fan, Ocean College, Zhejiang University, Zhou Shan, 316022, China
Deli Wang, State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Science, Xiamen University, Xiamen, 361102, China
Chen-Tung Arthur Chen, Institute of Marine Geology and Chemistry, National Sun Yat-Sen University, Taiwan, 080471, China
Yao Zhang, State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Science, Xiamen University, Xiamen, 361102, China
Presenter Email: chenmingming@xmu.edu.cn
[E-poster]      [POLIT]

Dinitrogen (N2) fixation provides nitrogen sources supporting active chemoautotrophic processes in submarine hydrothermal systems. Here, the diazotrophic phylogenetic diversity and N2 fixation profile are investigated in depth along a sharp biogeochemical gradient from the hydrothermal vents to ambient seawater in a shallow submarine hydrothermal system (SHS) off Kueishantao Islet, Taiwan. Diazotrophic community compositions in the SHS covered all four known nifH clusters (I, II, III, and IV) and contained both characteristics of diazotrophic communities in deep-sea hydrothermal systems and terrestrial geothermal systems. Abundant diazotrophs affiliated with Cluster I iron-reducing alpha/beta- and delta-proteobacteria, Cluster III green sulfur bacteria, Cluster III sulfate-reducing delta-proteobacteria, and Cluster I Firmicutes, along with small amounts of diazotrophic Cluster I epsilon-proteobacteria and cyanobacteria were retrieved from the hydrothermal vents and bottom waters, while Cluster I purple sulfur gamma-proteobacteria and diverse heterotrophic proteobacteria dominated seawater above the hydrothermal vents. The protein structure analysis further revealed that nitrogenase around the hydrothermal vents showed structural adaptations to high temperature, low pH, and sulfur-rich conditions. The low N2 fixation rates (NFRs) around the hydrothermal vents indicated that the chemolithotrophic diazotrophs there performed minor N2 fixation probably due to the existence of high concentrations of inorganic nitrogen compounds. In contrast, high NFRs were measured in the seawater directly above the hydrothermal vents probably owing to the exhausted nitrogen nutrients there and the potential supply of iron from the hydrothermal fluids. Notably, the high NFRs were driven by diverse heterotrophic diazotrophs. This study suggests that SHSs may be potential hotspots for marine N2 fixation.