title: An ecological network of polysaccharide utilization among human intestinal symbionts.
abstract: BACKGROUND
  The human intestine is colonized with trillions of microorganisms important to health and disease. There has been an intensive effort to catalog the species and genetic content of this microbial ecosystem. However, little is known of the ecological interactions between these microbes, a prerequisite to understanding the dynamics and stability of this host-associated microbial community. Here we perform a systematic investigation of public goods-based syntrophic interactions among the abundant human gut bacteria, the Bacteroidales.
  
  
  RESULTS
  We find evidence for a rich interaction network based on the breakdown and use of polysaccharides. Species that utilize a particular polysaccharide (producers) liberate polysaccharide breakdown products (PBPs) that are consumed by other species unable to grow on the polysaccharide alone (recipients). Cross-species gene addition experiments demonstrate that recipients can grow on a polysaccharide if the producer-derived glycoside hydrolase, responsible for PBP generation, is provided. These producer-derived glycoside hydrolases are public goods transported extracellularly in outer membrane vesicles allowing for the creation of PBP and concomitant recipient growth spatially distant from the producer. Recipients can exploit these ecological interactions and conditionally outgrow producers. Finally, we show that these public goods-based interactions occur among Bacteroidales species coresident within a natural human intestinal community.
  
  
  CONCLUSIONS
  This study examines public goods-based syntrophic interactions between bacterial members of the human gut microbial ecosystem. This polysaccharide-based network likely represents foundational relationships creating organized ecological units within the intestinal microbiota, knowledge of which can be applied to impact human health.
authors: Division of Infectious Diseases, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 181 Longwood Avenue, Boston, MA 02115, USA; Division of Infectious Diseases, Department of Medicine, Boston Children's Hospital and Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA.
authors: Seth
authors: S
authors: Rakoff-Nahoum
authors: Division of Infectious Diseases, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 181 Longwood Avenue, Boston, MA 02115, USA.
authors: Michael J
authors: MJ
authors: Coyne
authors: Division of Infectious Diseases, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 181 Longwood Avenue, Boston, MA 02115, USA. Electronic address: lcomstock@rics.bwh.harvard.edu.
authors: Laurie E
authors: LE
authors: Comstock
mesh_terms: D041963:Bacteroidetes / Q000378:metabolism*; D017753:Ecosystem; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000382:microbiology*; D011134:Polysaccharides / Q000378:metabolism*; D013559:Symbiosis
chemical_list: D011134:Polysaccharides