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Environ Microbiol. 2019 Jul;21(7):2533-2543. doi: 10.1111/1462-2920.14646. Epub 2019 May 31.

Molecular characteristics of microbially mediated transformations of Synechococcus-derived dissolved organic matter as revealed by incubation experiments.

Zheng Q1,2, Chen Q1,2, Cai R1,2, He C3, Guo W1,4, Wang Y1,2, Shi Q3, Chen C5,6, Jiao N1,2.

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State Key Laboratory for Marine Environmental Science, Collage of Ocean and Earth Sciences, Xiamen University, Xiamen, 361102, People's Republic of China.
Institute of Marine Microbes and Ecospheres, Xiamen University, Xiamen, 361102, People's Republic of China.
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China.
Key Laboratory of Coastal and Wetland Ecosystems, Ministry of Education, Xiamen University, Xiamen, People's Republic of China.
CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, People's Republic of China.
Xisha Deep Sea Marine Environment Observation and Research Station, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Sansha, People's Republic of China.


In this study, we investigated the microbially mediated transformation of labile Synechococcus-derived DOM to RDOM using a 60-day experimental incubation system. Three phases of TOC degradation activity (I, II and III) were observed following the addition of Synechococcus-derived DOM. The phases were characterized by organic carbon consumption rates of 8.77, 1.26 and 0.16 μmol L-1 day-1 , respectively. Excitation emission matrix analysis revealed the presence of three FDOM components including tyrosine-like, fulvic acid-like, and humic-like molecules. The three components also exhibited differing biological availabilities that could be considered as labile DOM (LDOM), semi-labile DOM (SLDOM) and RDOM, respectively. DOM molecular composition was also evaluated using FT-ICR MS. Based on differing biological turnover rates and normalized intensity values, a total of 1704 formulas were identified as candidate LDOM, SLDOM and RDOM molecules. Microbial transformation of LDOM to RDOM tended to proceed from high to low molecular weight, as well as from molecules with high to low double bond equivalent (DBE) values. Relatively higher aromaticity was observed in the formulas of RDOM molecules relative to those of LDOM molecules. FDOM components provide valuable proxy information to investigate variation in the bioavailability of DOM. These results suggest that coordinating fluorescence spectroscopy and FT-ICR MS of DOM, as conducted here, is an effective strategy to identify and characterize LDOM, SLDOM and RDOM molecules in incubation experiments emulating natural systems. The results described here provide greater insight into the metabolism of phytoplankton photosynthate by heterotrophic bacteria in marine environments.


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