Changes in bacterial community structure and humic acid composition in response to enhanced extracellular electron trans
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ORIGINAL PAPER
Changes in bacterial community structure and humic acid composition in response to enhanced extracellular electron transfer process in coastal sediment Jiulong Zhao1,2 · Long Wang1 · Lili Tang1 · Rui Ren4 · Wuxin You5 · Robina Farooq6 · Zejie Wang1,3 · Yongyu Zhang1 Received: 5 December 2018 / Revised: 25 February 2019 / Accepted: 10 April 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract Humic acids are one of the main organic matters in sediments and contribute importantly to the marine biogeochemical cycles. Extracellular electron transfer is a ubiquitous natural process and has potentials to change the macrostructure of humic acids which can act as an electron shuttle. By setting up marine sediment microbial fuel cells, the present study revealed that enhanced extracellular electron transfer process could increase the content of C and H, but decrease the O content in humic acids, which could result in an increased aromaticity and decreased polarity of humic acids, whereas no significant changes occurred to the humification degree of the humic acids. Specific bacterial groups as potential exoelectrogens including Proteobacteria (especially Pseudomonas strains) and Firmicutes were enriched under enhanced extracellular electron transfer process, indicating that they were active to exchange electrons and might play important roles during the changes of humic acids, while the relative abundance of Verrucomicrobia and Bacteroidetes was reduced during these processes. The results of the present research shed lights on the relation between exoelectrogens and the transformation of humic acids in coastal sediment, while the microbial process and mechanisms behind it require further study. Keywords Humic acids · Extracellular electron transfer · Exoelectrogens · Bacterial community structure · Sediment microbial fuel cell
Introduction Communicated by Erko Stackebrandt. * Zejie Wang [email protected] 1
Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
College of Environmental Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
4
State Key Laboratory of Marine Environmental Science, Institute of Marine Microbes and Ecospheres, Xiamen University, Xiamen 361101, China
5
Plant Biochemistry, Ruhr University Bochum, 44801 Bochum, Germany
6
Department of Chemical Engineering, COMSATS Institute of Information Technology, Lahore, Pakistan
Humic substances (HSs) spread widely in natural environments such as water body and sediments, accounting for ~ 60% of organic matter in aquatic ecosystems and 70–80% in mineral soils (Schlesinger 1997; Stevenson 1994). HSs are auto-assembled in supramolecular associations comprising of relatively small molecules with similar characteristics which held together
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