Qian Liu

Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources,China

Title: Dissolved free amino acids and polyamines are two major dissolved organic nitrogen sources for marine bacterioplankton

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Biography

Dr. Qian Liu earned her Ph.D. in Biological Oceanography from the University of Georgia in 2016 and currently works as an Associate Scientist in the Second Institute of Oceanography, Ministry of Natural Resources, China. She is one of the participants in Biological Observations Task Force of the POGO. Her research is primarily focusing on two aspects: 1) diversity and ecological functions of microorganisms in coastal and open ocean; 2) microbial driven biogeochemical nitrogen cycling. She uses innovative geochemical tracer approaches, including radio- and stable isotopes, with mesocosm and in situ experiment to quantify nitrogen cycling pathways and fates, in combination with omics techniques (e.g., genomics, metagenomics) to investigate the mechanisms of nitrogen cycling driven by microorganisms. Her research has been published in the ISME Journal, Biogeochemistry, MEPS, JGR, etc.

Abstract

The regenerated nitrogen from dissolved organic nitrogen (DON) has been suggested to play a pivotal role in sustaining primary productivity in marine environments; however, DON cycling has not been clarified there. Dissolved free amino acids (DFAAs) and polyamines (DFPAs) are two major groups of labile DON that are used rapidly by heterotrophic bacteria, and important in nitrogen cycling. In this study, we applied radio-isotope labelled compounds for measuring turnover rates and HPLC for quantifying concentrations of representative DFAAs (arginine and glutamic acid) and DFPAs (putrescine) in riverine, estuary and coastal shelf waters, to estimate uptake rates and evaluate their potentials to fulfill carbon and nitrogen demands of bacterial production. Furthermore, homologs of genes encoding transporter systems for arginine (aotJ) and putrescine (potD/potF) were quantified in metagenomes from sampling stations. The taxa encoding these genes were identified to gain insight into the composition of microbial communities potentially utilizing DFAAs and DFPAs. Spatial variation in uptake rates indicated that biogeochemical cycling of DFAAs was distinct from that of DFPAs. Redundancy analysis and metagenomes demonstrated that environmental variables and distinction in bacterial assemblages using DFAAs and DFPAs could both affect their dynamics in marine environments.