Specificity of Associations between Bacteria and the Coral Pocillopora meandrina during Early Development

Abstract

cRelationships between corals and specific bacterial associates are thought to play an important role in coral health. In this study, the specificity of bacteria associating with the coral Pocillopora meandrina was investigated by exposing coral embryos to various strains of cultured marine bacteria, sterile seawater, or raw seawater and examining the identity, density, and location of incorporated cells. The isolates utilized in this experiment included members of the Roseobacter and SAR11 clades of the Alphaproteobacteria, a Pseudoalteromonas species of the Gammaproteobacteria, and a Synechococcus species of the Cyanobacteria phylum. Based on terminal restriction fragment length polymorphism analysis of small-subunit rRNA genes, similarities in bacterial communities associated with 170-h-old planulae were observed regardless of treatment, suggesting that bacteria may have been externally associated from the outset of the experiment. Microscopic examination of P. meandrina planulae by fluorescence in situ hybridization with bacterial and Roseobacter clade-specific oligonucleotide probes revealed differences in the densities and locations of planulae-associated cells. Planulae exposed to either raw seawater or strains of Pseudoalteromonas and Roseobacter harbored the highest densities of internally associated cells, of which 20 to 100% belonged to the Roseobacter clade. Planulae exposed to sterile seawater or strains of the SAR11 clade and Synechococcus did not show evidence of prominent bacterial associations. Additional analysis of the raw-seawater-exposed planulae via electron microscopy confirmed the presence of internally associated prokaryotic cells, as well as virus-like particles. These results suggest that the availability of specific microorganisms may be an important factor in the establishment of coral-bacterial relationships.

Onset and establishment of diazotrophs and other bacterial associates in the early life history stages of the coral Acropora millepora

“…A number of recent studies provide corroborative evidence that Roseobacter is a dominant bacterial group in very early developmental stages of corals (Apprill et al . , ; Sharp et al . ; Ceh et al .…”

“…In the broadcast‐spawning species Pocillopora meandrina, the absence of bacteria in oocytes and newly released larvae, but presence in 1‐week‐old larvae, suggests that horizontal transmission may occur in spawning species (Apprill et al . , ). The pattern emerging from this limited number of studies is consistent with transmission mode of bacterial communities being determined by reproductive mode (i.e.…”

A microbial perspective on the life‐history evolution of marine invertebrate larvae: If, where and when to feed

“…Recent efforts to describe the dynamics and structure of larval–microbiome interactions have suggested that this microbial community is specific to the larval host species while remaining distinct from the environmental metagenome (Apprill et al, ; Galac, Bosch, & Janies, ; Lema et al, ; Mortzfeld et al., ). These patterns are consistent with other taxa and their developmental stages (Gilbert, ; Gilbert, Bosch, & Ledón‐Rettig, ; McFall‐Ngai, ; McFall‐Ngai & Ruby, ; Rosenberg & Zilber‐Rosenberg, ; Schwab et al, ; Walker & Lesser, ).…”

Evolutionary Ecology of the Marine Roseobacter Clade

“…As is the case for Roseobacter interactions with other eukaryotes, it is not yet clear whether a physical association signifies a specific mutualistic interaction. There is evidence that roseobac-ters may play a role in coral reproduction, based on both consistent associations between the bacteria and early developmental stages of corals (112,113) as well as increases in Roseobacter abundance after coral mass spawning (114). Roseobacters may also have a role in coral bleaching by acting as probiotics against pathogens (115, 116).…”