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mSphere. 2019 Jan 23;4(1). pii: e00436-18. doi: 10.1128/mSphere.00436-18.

Extracellular Electron Transfer May Be an Overlooked Contribution to Pelagic Respiration in Humic-Rich Freshwater Lakes.

Author information

1
Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
2
Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA.
3
Département des Sciences Biologiques, Université du Québec à Montréal (UQAM), Montréal, Quebec, Canada.
4
Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA trina.mcmahon@wisc.edu.
5
Department of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA.

Abstract

Humic lakes and ponds receive large amounts of terrestrial carbon and are important components of the global carbon cycle, yet how their redox cycling influences the carbon budget is not fully understood. Here we compared metagenomes obtained from a humic bog and a clear-water eutrophic lake and found a much larger number of genes that might be involved in extracellular electron transfer (EET) for iron redox reactions and humic substance (HS) reduction in the bog than in the clear-water lake, consistent with the much higher iron and HS levels in the bog. These genes were particularly rich in the bog's anoxic hypolimnion and were found in diverse bacterial lineages, some of which are relatives of known iron oxidizers or iron-HS reducers. We hypothesize that HS may be a previously overlooked electron acceptor and that EET-enabled redox cycling may be important in pelagic respiration and greenhouse gas budget in humic-rich freshwater lakes.

KEYWORDS:

Cyc2; EET; Fe; HS; MHC; PCC; extracellular electron transfer; humic lake; humic substances; iron; multiheme cytochrome c; porin-cytochrome c complex; redox cycling

PMID:
30674644
PMCID:
PMC6344600
DOI:
10.1128/mSphere.00436-18
[Indexed for MEDLINE]
Free PMC Article

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