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.

Macroalgal–bacterial interactions: Role of dimethylsulfoniopropionate in microbial gardening by Ulva (Chlorophyta)

“…Our results are supported by previously reported chemotactic response factors to the same concentrations of DMSP among coral‐associated bacteria (Tout et al., ). Besides DMSP, there might be other metabolites which attract Roseovarius sp.…”

“…Similar to the protocol by Tout et al. (), the chemoattractant gradually leaks into the external environment through the pipette tip via molecular diffusion, creating a gradient in the surrounding sea water that triggers the migration of chemotactic bacteria into the pipette. After 5 or 10 min of deployment, the capillary contents were sampled.…”

Microbial Surface Colonization and Biofilm Development in Marine Environments

“…was found to be chemotactic toward inorganic phosphate during starvation, a behavior consistent with its natural habitat of the ultraoligotrophic eastern Mediterranean Sea (393). A recent study showed that coral surfaceassociated bacteria exhibited significantly higher levels of chemotaxis than free-living bacteria in nearby non-coral-associated waters (394). Numerous processes, such as cell lysis, phytoplankton exudation, animal excretion, food vacuole egestion, and particle degradation and dissolution, provide point sources rich in organic substrates and inorganic nutrients in marine waters (186,392,395).…”

Temperature-induced behavioral switches in a bacterial coral pathogen

“…Under business as usual forecasts for greenhouse gas emissions, it is projected that pathogen virulence will increase for 440% of reefs worldwide by 2030 (Maynard et al, 2015). Given that all currently known putative coral pathogens are motile (Garren et al, 2014) and that chemotaxis is both a common feature in the reef environment (Tout et al, 2015a) and implicated in the success of bacterial pathogens of corals (Banin et al, 2001;Meron et al, 2009), our observations that both chemotactic and chemokinetic behaviors of V. coralliilyticus are influenced by temperature add to our current understanding of coral disease to suggest that motility adaptations under future climate scenarios have the potential to favor bacterial pathogens over their coral hosts (Garren et al, 2014;Maynard et al, 2015).…”