title: Acromyrmex Leaf-Cutting Ants Have Simple Gut Microbiota with Nitrogen-Fixing Potential.
abstract: Ants and termites have independently evolved obligate fungus-farming mutualisms, but their gardening procedures are fundamentally different, as the termites predigest their plant substrate whereas the ants deposit it directly on the fungus garden. Fungus-growing termites retained diverse gut microbiota, but bacterial gut communities in fungus-growing leaf-cutting ants have not been investigated, so it is unknown whether and how they are specialized on an exclusively fungal diet. Here we characterized the gut bacterial community of Panamanian Acromyrmex species, which are dominated by only four bacterial taxa: Wolbachia, Rhizobiales, and two Entomoplasmatales taxa. We show that the Entomoplasmatales can be both intracellular and extracellular across different gut tissues, Wolbachia is mainly but not exclusively intracellular, and the Rhizobiales species is strictly extracellular and confined to the gut lumen, where it forms biofilms along the hindgut cuticle supported by an adhesive matrix of polysaccharides. Tetracycline diets eliminated the Entomoplasmatales symbionts but hardly affected Wolbachia and only moderately reduced the Rhizobiales, suggesting that the latter are protected by the biofilm matrix. We show that the Rhizobiales symbiont produces bacterial NifH proteins that have been associated with the fixation of nitrogen, suggesting that these compartmentalized hindgut symbionts alleviate nutritional constraints emanating from an exclusive fungus garden diet reared on a substrate of leaves.
authors.affiliation: Centre for Social Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark sapountzis@bio.ku.dk jjboomsma@bio.ku.dk.
authors.forename: Panagiotis
authors.identifier: http://orcid.org/0000-0001-6286-3918
authors.initials: P
authors.lastname: Sapountzis
authors.affiliation: Centre for Social Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia.
authors.forename: Mariya
authors.initials: M
authors.lastname: Zhukova
authors.affiliation: Molecular Microbial Ecology Group, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Lars H
authors.initials: LH
authors.lastname: Hansen
authors.affiliation: Molecular Microbial Ecology Group, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Søren J
authors.initials: SJ
authors.lastname: Sørensen
authors.affiliation: Centre for Social Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Morten
authors.initials: M
authors.lastname: Schiøtt
authors.affiliation: Centre for Social Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark sapountzis@bio.ku.dk jjboomsma@bio.ku.dk.
authors.forename: Jacobus J
authors.identifier: http://orcid.org/0000-0002-3598-1609
authors.initials: JJ
authors.lastname: Boomsma
mesh_terms: D020561:Alphaproteobacteria / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D000818:Animals; D001000:Ants / Q000382:microbiology*; D060366:Entomoplasmatales / Q000302:isolation & purification* / Q000502:physiology; D000069196:Gastrointestinal Microbiome; D009586:Nitrogen Fixation; D010088:Oxidoreductases / Q000235:genetics; D013559:Symbiosis; D020577:Wolbachia / Q000302:isolation & purification* / Q000502:physiology
chemical_list: D010088:Oxidoreductases; C029130:nitrogenase reductase