AUTHOR=Zhou Guo-Wei , Yang Xiao-Ru , Marshall Christopher W. , Li Hu , Zheng Bang-Xiao , Yan Yu , Su Jian-Qiang , Zhu Yong-Guan 

TITLE=Biochar Addition Increases the Rates of Dissimilatory Iron Reduction and Methanogenesis in Ferrihydrite Enrichments

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.00589

DOI=10.3389/fmicb.2017.00589

ISSN=1664-302X

ABSTRACT=<p>Biochar contains quinones and aromatic structures that facilitate extracellular electron transfer between microbial cells and insoluble minerals. In this study, granulated biochar (1.2–2 mm) and powdered biochar (&lt;0.15 mm) were amended to two ferrihydrite (<italic>in situ</italic> ferrihydrite and <italic>ex situ</italic> ferrihydrite) enrichments to investigate the effect of biochar with different particle sizes on dissimilatory iron(III)-reducing bacteria (DIRB) and methanogens. Biochar addition significantly stimulated the reduction of both <italic>in situ</italic> ferrihydrite and <italic>ex situ</italic> ferrihydrite and the production of methane. Powdered biochar amendments increased iron reduction compared to granulated biochar amendment in both the <italic>in situ</italic> ferrihydrite and <italic>ex situ</italic> ferrihydrite enrichments. However, no significant difference was observed in methane production between the powdered biochar and granulated biochar amendments in the two ferrihydrite enrichments. Analysis of 16S <italic>rRNA</italic> gene sequences showed that both DIRB and methanogens were enriched after biochar amendments in the <italic>in situ</italic> ferrihydrite and <italic>ex situ</italic> ferrihydrite enrichments. Taxa belonging to the Geobacteraceae and methanogenic genus affiliated to <italic>Methanosarcina</italic> were detected with significantly higher relative abundances in powdered biochar amendments than those in granulated biochar amendments in both the ferrihydrite enrichments. X-ray diffraction analysis indicated green rust [Fe<sub>2</sub>(CO<sub>3</sub>) (OH)] and vivianite [Fe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> 8(H<sub>2</sub>O)] formed in the <italic>ex situ</italic> ferrihydrite and <italic>in situ</italic> ferrihydrite enrichments without biochar addition, respectively. After granulated biochar amendment, the mineral phase changed from the green rust to vivianite in the <italic>ex situ</italic> ferrihydrite enrichment, while crystalline vivianite and iron oxide (γ-Fe<sub>2</sub>O<sub>3</sub>) were detected simultaneously in the <italic>in situ</italic> ferrihydrite enrichment. No crystalline iron compound was found in the powdered biochar amendments in both ferrihydrite enrichments. Overall, our study illustrated that the addition of biochar affected iron-reducing and methane-generating microbial communities to some extent.</p>