title: Compartmentalized microbial composition, oxygen gradients and nitrogen fixation in the gut of Odontotaenius disjunctus.
abstract: Coarse woody debris is an important biomass pool in forest ecosystems that numerous groups of insects have evolved to take advantage of. These insects are ecologically important and represent useful natural analogs for biomass to biofuel conversion. Using a range of molecular approaches combined with microelectrode measurements of oxygen, we have characterized the gut microbiome and physiology of Odontotaenius disjunctus, a wood-feeding beetle native to the eastern United States. We hypothesized that morphological and physiological differences among gut regions would correspond to distinct microbial populations and activities. In fact, significantly different communities were found in the foregut (FG), midgut (MG)/posterior hindgut (PHG) and anterior hindgut (AHG), with Actinobacteria and Rhizobiales being more abundant toward the FG and PHG. Conversely, fermentative bacteria such as Bacteroidetes and Clostridia were more abundant in the AHG, and also the sole region where methanogenic Archaea were detected. Although each gut region possessed an anaerobic core, micron-scale profiling identified radial gradients in oxygen concentration in all regions. Nitrogen fixation was confirmed by (15)N2 incorporation, and nitrogenase gene (nifH) expression was greatest in the AHG. Phylogenetic analysis of nifH identified the most abundant transcript as related to Ni-Fe nitrogenase of a Bacteroidetes species, Paludibacter propionicigenes. Overall, we demonstrate not only a compartmentalized microbiome in this beetle digestive tract but also sharp oxygen gradients that may permit aerobic and anaerobic metabolism to occur within the same regions in close proximity. We provide evidence for the microbial fixation of N2 that is important for this beetle to subsist on woody biomass.
authors.affiliation: Ecology Department, Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Javier A
authors.initials: JA
authors.lastname: Ceja-Navarro
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA, USA.
authors.forename: Nhu H
authors.initials: NH
authors.lastname: Nguyen
authors.affiliation: Ecology Department, Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Ulas
authors.initials: U
authors.lastname: Karaoz
authors.affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, USA.
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Gross
authors.affiliation: Department of Environmental Science Policy and Management, University of California, Berkeley, CA, USA.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Herman
authors.affiliation: Ecology Department, Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Gary L
authors.initials: GL
authors.lastname: Andersen
authors.affiliation: Ecology Department, Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Bruns
authors.affiliation: Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Pett-Ridge
authors.affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, USA.
authors.forename: Meredith
authors.initials: M
authors.lastname: Blackwell
authors.affiliation: 1] Ecology Department, Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA [2] Department of Environmental Science Policy and Management, University of California, Berkeley, CA, USA.
authors.forename: Eoin L
authors.initials: EL
authors.lastname: Brodie
mesh_terms: D000818:Animals; D001105:Archaea / Q000235:genetics; D001419:Bacteria / Q000145:classification / Q000235:genetics; D044822:Biodiversity; D001517:Coleoptera / Q000382:microbiology*; D041981:Gastrointestinal Tract / Q000737:chemistry / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics / Q000502:physiology*; D010088:Oxidoreductases / Q000235:genetics; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D012336:RNA, Ribosomal, 16S; D010088:Oxidoreductases; C029130:nitrogenase reductase; D010100:Oxygen