title: NifH-Harboring Bacterial Community Composition across an Alaskan Permafrost Thaw Gradient.
abstract: Since nitrogen (N) is often limiting in permafrost soils, we investigated the N2-fixing genetic potential and the inferred taxa harboring those genes by sequencingnifHgene fragments in samples taken along a permafrost thaw gradient in an Alaskan boreal soil. Samples from minimally, moderately and extensively thawed sites were taken to a depth of 79 cm to encompass zones above and below the depth of the water table.NifHreads were translated with frameshift correction and 112,476 sequences were clustered at 5% amino acid dissimilarity resulting in 1,631 OTUs. Sample depth in relation to water table depth was correlated to differences in theNifHsequence classes with those most closely related to group InifH-harboring Alpha- and Beta-Proteobacteria in higher abundance above water table depth while those related to group IIInifH-harboring Delta Proteobacteria more abundant below. The most dominant below water table depthNifHsequences, comprising 1/3 of the total, were distantly related toVerrucomicrobia-Opitutaceae. Overall, these results suggest that permafrost thaw alters the class-level composition of N2-fixing communities in the thawed soil layers and that this distinction corresponds to the depth of the water table. ThesenifHdata were also compared tonifHsequences obtained from a study at an Alaskan taiga site, and to those of other geographically distant, non-permafrost sites. The two Alaska sites were differentiated largely by changes in relative abundances of the same OTUs, whereas the non-Alaska sites were differentiated by the lack of many Alaskan OTUs, and the presence of unique halophilic, sulfate- and iron-reducing taxa in the Alaska sites.
authors.affiliation: College of Integrative Sciences and Arts, Arizona State UniversityMesa, AZ, USA; Arizona State University, Center for Fundamental and Applied Microbiomics, Biodesign InstituteTempe, AZ, USA.
authors.forename: C Ryan
authors.initials: CR
authors.lastname: Penton
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of OklahomaNorman, OK, USA; Key Lab of the Ministry of Education for Coastal and Wetland Ecosystems, School of Environmental Sciences, Xiamen UniversityXiamen, China.
authors.forename: Caiyun
authors.initials: C
authors.lastname: Yang
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma Norman, OK, USA.
authors.forename: Liyou
authors.initials: L
authors.lastname: Wu
authors.affiliation: Center for Microbial Ecology, Michigan State University East Lansing, MI, USA.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma Norman, OK, USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma Norman, OK, USA.
authors.forename: Feifei
authors.initials: F
authors.lastname: Liu
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma Norman, OK, USA.
authors.forename: Yujia
authors.initials: Y
authors.lastname: Qin
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma Norman, OK, USA.
authors.forename: Ye
authors.initials: Y
authors.lastname: Deng
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma Norman, OK, USA.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Hemme
authors.affiliation: Key Lab of the Ministry of Education for Coastal and Wetland Ecosystems, School of Environmental Sciences, Xiamen University Xiamen, China.
authors.forename: Tianling
authors.initials: T
authors.lastname: Zheng
authors.affiliation: Department of Biological Sciences, Northern Arizona University Flagstaff, AZ, USA.
authors.forename: Edward A G
authors.initials: EA
authors.lastname: Schuur
authors.affiliation: Center for Microbial Ecology, Michigan State University East Lansing, MI, USA.
authors.forename: James
authors.initials: J
authors.lastname: Tiedje
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of OklahomaNorman, OK, USA; Earth Sciences Division, Lawrence Berkeley National LaboratoryBerkeley, CA, USA; State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua UniversityBeijing, China.
authors.forename: Jizhong
authors.initials: J
authors.lastname: Zhou
keywords: diazotroph; microbial; nifH; nitrogen; nitrogen-fixing; permafrost