Global Networks of Symbiodinium-Bacteria Within the Coral Holobiont

Abstract

Scleractinian corals form the framework of coral reefs and host abundant and diverse microbial communities that are fundamental to their success. A very limited number of studies have examined the co-occurrence of multiple partners within the coral 'holobiont' and their pattern of specificity over different geographical scales. In this study, we explored two molecular sequence datasets representing associations between corals and dinoflagellates in the genus Symbiodinium and between corals and bacteria, across the globe. Through a network theory approach, we characterised patterns of co-occurrences between bacteria and Symbiodinium with 13 coral genera across six water basins. The majority of the bacteria-Symbiodinium co-occurrences were specific to either a coral genus or water basin, emphasising both coral host and environment as important factors driving the diversity of coral assemblages. Yet, results also identified bacteria and Symbiodinium that were shared by multiple coral genera across several water basins. The analyses indicate that shared co-occurrences are independent of the phylogenetic and biogeographic relationship of coral hosts.

Revealing changes in the microbiome of Symbiodiniaceae under thermal stress

“…The relationship between Symbiodiniaceae and their associated bacterial communities has been studied in significantly less detail than bacterial‐coral or Symbiodiniaceae‐coral associations (Lawson et al ., ), which is surprising given the fact that species‐specific algal‐bacterial interactions have been reported to directly or indirectly influence both partners (Bolch et al ., ). Recent work using network analysis to examine Symbiodiniaceae‐bacterial associations across water basins and coral hosts suggests complementary interactions between microbial communities that need to be considered (Bernasconi et al ., ). For example, Bernasconi et al .…”

“…For example, Bernasconi et al . () report some bacterial‐Symbiodiniaceae co‐occurrences within the coral holobiont (e.g., Vibrio ) that occur independently of phylogeny or geographic location. Within our study, no core zOTUs were shared across all Symbiodiniaceae strains, although Labrenzia and two unassigned bacteria were core genera (Supporting Information Fig.…”

Symbiodiniaceae‐bacteria interactions: rethinking metabolite exchange in reef‐building corals as multi‐partner metabolic networks

“…Only a few studies have specifically considered Symbiodiniaceae‐bacterial interactions in the coral holobiont, with their results pointing to the potentially critical role that these partnerships might play in regulating holobiont nutrient cycling and competitive fitness (Ritchie, ; Bourne et al ., ; Ainsworth et al ., ; Peixoto et al ., ; Silveira et al ., ; Bernasconi et al ., ); Table ). For example, some coral‐associated bacteria can rapidly take up organosulfur compounds released by Symbiodiniaceae cells, such as dimethylsulfoniopropionate (DMSP), to sustain their growth and produce an antimicrobial compound active against common coral pathogens (Raina et al ., ; Raina et al ., ).…”

“…Numerous studies have demonstrated that both endosymbiotic Symbiodiniaceae and associated bacteria support the persistence of corals through the exchange of metabolites and bioactive compounds (Rohwer et al ., ; Cantin et al ., ; Ainsworth et al ., ; Bourne et al ., ; Glasl et al ., ; Peixoto et al ., ; Hillyer et al ., ; Matthews et al ., ). Yet, remarkably, the role of bacteria in regulating Symbiodiniaceae resource acquisition, competitive performance and functional diversity (as both free‐living and endosymbionts) is relatively unexplored (Ritchie, ; Bourne et al ., ; Ainsworth et al ., ; Peixoto et al ., ; Silveira et al ., ; Bernasconi et al ., ); Table ). This fundamental gap in knowledge wholly constrains our understanding of how microbes act in concert to regulate the health of coral holobionts, especially given the importance of bacterial‐algal interactions for nutrient cycling, signal transduction and gene transfer as demonstrated for other microalgal taxa (Seymour et al ., ).…”

“…Emerging evidence suggests that interactions with bacterial associates may be important for Symbiodiniaceae nutrition and survival in their free‐living state (Jeong et al ., ; Frommlet et al ., ; Lawson et al ., ). Furthermore, global cooccurrence of specific bacterial taxa and Symbiodiniaceae in corals (Bernasconi et al ., ) and co‐localisation of distinct bacterial taxa with Symbiodiniaceae in cnidarian host tissues (Ainsworth et al ., ) suggest specific Symbiodiniaceae‐bacterial interactions may be crucial to support holobiont metabolic functioning. Exploring Symbiodiniaceae‐bacteria associations is therefore a logical next step toward fully understanding the complex symbiotic interactions occurring in the coral holobiont and assists development of conservation strategies for reefs under global climate change (van Oppen and Blackall, ).…”