title: Disturbance induced decoupling between host genetics and composition of the associated microbiome.
abstract: BACKGROUND
  Studies of oyster microbiomes have revealed that a limited number of microbes, including pathogens, can dominate microbial communities in host tissues such as gills and gut. Much of the bacterial diversity however remains underexplored and unexplained, although environmental conditions and host genetics have been implicated. We used 454 next generation 16S rRNA amplicon sequencing of individually tagged PCR reactions to explore the diversity of bacterial communities in gill tissue of the invasive Pacific oyster Crassostrea gigas stemming from genetically differentiated beds under ambient outdoor conditions and after a multifaceted disturbance treatment imposing stress on the host.
  
  
  RESULTS
  While the gill associated microbial communities in oysters were dominated by few abundant taxa (i.e. Sphingomonas, Mycoplasma) the distribution of rare bacterial groups correlated to relatedness between the hosts under ambient conditions. Exposing the host to disturbance broke apart this relationship by removing rare phylotypes thereby reducing overall microbial diversity. Shifts in the microbiome composition in response to stress did not result in a net increase in genera known to contain potentially pathogenic strains.
  
  
  CONCLUSIONS
  The decrease in microbial diversity and the disassociation between population genetic structure of the hosts and their associated microbiome suggest that disturbance (i.e. stress) may play a significant role for the assembly of the natural microbiome. Such community shifts may in turn also feed back on the course of disease and the occurrence of mass mortality events in oyster populations.
authors.affiliation: Helmholtz Centre for Polar and Marine Research, Alfred Wegener Institute, Coastal Ecology, Wadden Sea Station Sylt, Hafenstrasse 43, 25992, List/Sylt, Germany. mathias.wegner@awi.de.
authors.forename: Karl Mathias
authors.initials: KM
authors.lastname: Wegner
authors.forename: Nils
authors.initials: N
authors.lastname: Volkenborn
authors.forename: Hannes
authors.initials: H
authors.lastname: Peter
authors.forename: Alexander
authors.initials: A
authors.lastname: Eiler
mesh_terms: D000818:Animals; D001419:Bacteria / Q000145:classification* / Q000235:genetics*; D049896:Crassostrea / Q000382:microbiology*; D041981:Gastrointestinal Tract / Q000382:microbiology; D005880:Gills / Q000382:microbiology; D064307:Microbiota; D016133:Polymerase Chain Reaction; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013312:Stress, Physiological
chemical_list: D012336:RNA, Ribosomal, 16S