title: Where less may be more: how the rare biosphere pulls ecosystems strings.
abstract: Rare species are increasingly recognized as crucial, yet vulnerable components of Earth's ecosystems. This is also true for microbial communities, which are typically composed of a high number of relatively rare species. Recent studies have demonstrated that rare species can have an over-proportional role in biogeochemical cycles and may be a hidden driver of microbiome function. In this review, we provide an ecological overview of the rare microbial biosphere, including causes of rarity and the impacts of rare species on ecosystem functioning. We discuss how rare species can have a preponderant role for local biodiversity and species turnover with rarity potentially bound to phylogenetically conserved features. Rare microbes may therefore be overlooked keystone species regulating the functioning of host-associated, terrestrial and aquatic environments. We conclude this review with recommendations to guide scientists interested in investigating this rapidly emerging research area.
authors.affiliation: Utrecht University, Department of Biology, Institute of Environmental Biology, Ecology and Biodiversity Group, Utrecht, The Netherlands.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Jousset
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.|Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Bienhold
authors.affiliation: Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany.|German Centre for Integrative Biodiversity Research (iDiv), Halle-Jena-Leipzig, Leipzig, Germany.
authors.forename: Antonis
authors.initials: A
authors.lastname: Chatzinotas
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland.|Center for Invasion Biology, Department of Botany & Zoology, Stellenbosch University, Matieland, South Africa.
authors.forename: Laure
authors.initials: L
authors.lastname: Gallien
authors.affiliation: Sorbonne Universités, UPMC Université Paris 06, CNRS, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, F-29688, Roscoff Cedex, France.
authors.forename: Angélique
authors.initials: A
authors.lastname: Gobet
authors.affiliation: Netherlands Institute of Ecology, Department of Terrestrial Ecology, Wageningen, The Netherlands.
authors.forename: Viola
authors.initials: V
authors.lastname: Kurm
authors.affiliation: Friedrich Schiller University Jena, Institute of Ecology, Jena, Germany.|German Centre for Integrative Biodiversity Research (iDiv), Halle-Jena-Leipzig, Leipzig, Germany.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Küsel
authors.affiliation: Freie Universtät Berlin, Institute of Biology, Berlin, Germany.|Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Berlin, Germany.
authors.forename: Matthias C
authors.initials: MC
authors.lastname: Rillig
authors.affiliation: Imperial College London, Department of Life Sciences, Silwood Park Campus, Ascot, UK.
authors.forename: Damian W
authors.initials: DW
authors.lastname: Rivett
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, The Netherlands.
authors.forename: Joana F
authors.initials: JF
authors.lastname: Salles
authors.affiliation: Plant-Soil Interactions, Institute for Sustainability Sciences, Agroscope, Zürich, Switzerland.|Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland.|Plant-microbe Interactions, Institute of Environmental Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands.
authors.forename: Marcel G A
authors.initials: MG
authors.lastname: van der Heijden
authors.affiliation: Oklahoma State University, Department of Microbiology and Molecular Genetics, Stillwater, OK, USA.
authors.forename: Noha H
authors.initials: NH
authors.lastname: Youssef
authors.affiliation: State Key Laboratory of Pollution Control & Resource Reuse, School of the Environment, Nanjing University, Nanjing, China.
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Nanjing Agricultural University, Nanjing, China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Wei
authors.affiliation: Netherlands Institute of Ecology, Department of Terrestrial Ecology, Wageningen, The Netherlands.
authors.forename: W H Gera
authors.initials: WH
authors.lastname: Hol
mesh_terms: D001419:Bacteria / Q000145:classification*; D017753:Ecosystem; D004783:Environmental Microbiology; D010802:Phylogeny