title: Chemotaxis by natural populations of coral reef bacteria.
abstract: Corals experience intimate associations with distinct populations of marine microorganisms, but the microbial behaviours underpinning these relationships are poorly understood. There is evidence that chemotaxis is pivotal to the infection process of corals by pathogenic bacteria, but this evidence is limited to experiments using cultured isolates under laboratory conditions. We measured the chemotactic capabilities of natural populations of coral-associated bacteria towards chemicals released by corals and their symbionts, including amino acids, carbohydrates, ammonium and dimethylsulfoniopropionate (DMSP). Laboratory experiments, using a modified capillary assay, and in situ measurements, using a novel microfabricated in situ chemotaxis assay, were employed to quantify the chemotactic responses of natural microbial assemblages on the Great Barrier Reef. Both approaches showed that bacteria associated with the surface of the coral species Pocillopora damicornis and Acropora aspera exhibited significant levels of chemotaxis, particularly towards DMSP and amino acids, and that these levels of chemotaxis were significantly higher than that of bacteria inhabiting nearby, non-coral-associated waters. This pattern was supported by a significantly higher abundance of chemotaxis and motility genes in metagenomes within coral-associated water types. The phylogenetic composition of the coral-associated chemotactic microorganisms, determined using 16S rRNA amplicon pyrosequencing, differed from the community in the seawater surrounding the coral and comprised known coral associates, including potentially pathogenic Vibrio species. These findings indicate that motility and chemotaxis are prevalent phenotypes among coral-associated bacteria, and we propose that chemotaxis has an important role in the establishment and maintenance of specific coral-microbe associations, which may ultimately influence the health and stability of the coral holobiont.
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, New South Wales, Australia.
authors.forename: Jessica
authors.initials: J
authors.lastname: Tout
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, New South Wales, Australia.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Jeffries
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, New South Wales, Australia.
authors.forename: Katherina
authors.initials: K
authors.lastname: Petrou
authors.affiliation: Australian Centre for Ecogenomics, School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, Queensland, Australia.
authors.forename: Gene W
authors.initials: GW
authors.lastname: Tyson
authors.affiliation: Australian Institute of Marine Science, Townsville, Queensland, Australia.
authors.forename: Nicole S
authors.initials: NS
authors.lastname: Webster
authors.affiliation: Department of Civil and Environmental Engineering, Ralph M. Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Melissa
authors.initials: M
authors.lastname: Garren
authors.affiliation: Department of Civil and Environmental Engineering, Ralph M. Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Roman
authors.initials: R
authors.lastname: Stocker
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, New South Wales, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Ralph
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, New South Wales, Australia.
authors.forename: Justin R
authors.initials: JR
authors.lastname: Seymour
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000382:microbiology*; D001419:Bacteria / Q000187:drug effects* / Q000235:genetics; D002630:Chemotactic Factors / Q000494:pharmacology; D002633:Chemotaxis / Q000187:drug effects*; D057894:Coral Reefs; D004269:DNA, Bacterial / Q000032:analysis; D054892:Metagenome; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012623:Seawater / Q000382:microbiology; D013452:Sulfonium Compounds / Q000494:pharmacology; D014733:Vibrio / Q000235:genetics
chemical_list: D002630:Chemotactic Factors; D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D013452:Sulfonium Compounds; C068078:dimethylpropiothetin