Patterns of bacteria-host associations suggest different ecological strategies between two reef building cold-water coral species

Abstract

Cold-water corals (CWC) are main ecosystem engineers of the deep sea, and their reefs constitute hotspots of biodiversity. However, their ecology remains poorly understood, particularly, the nature of the holobiont formed by corals with their associated bacterial communities. Here, we analysed Madrepora oculata and Lophelia pertusa samples, collected from one location in a Mediterranean canyon in two different seasons (autumn and spring), in order to test for species specificity and temporal stability of the host-bacteria associations. The 16S rRNA sequencing revealed host-specific patterns of bacterial communities associated with L. pertusa and M. oculata, both in terms of community composition and diversity. All analyzed M. oculata polyps exhibited temporally and spatially similar bacterial communities dominated by haplotypes homologous to the known cnidarians-associated genus Endozoicomonas. In contrast, the bacterial communities associated with L. pertusa varied among polyps from the same colony, as well as among distinct colonies and between seasons. While the resilient consortium formed by M. oculata and its bacterial community fit the definition of holobiont, the versatility of the L. pertusa microbiome suggests that this association is more influenced by the environmental conditions or nutritional status. Our results thus highlight distinct host/microbes association strategies for these two closely related Scleractinians sharing the same habitat, suggesting distinct sensitivity to environmental change. Highlights ► We examine the bacterial communities of two reef-building cold-water coral species from Mediterranean Sea ► The 16S rRNA sequencing revealed host-specific patterns of bacterial communities both in terms of community composition and diversity ► Our results highlight distinct host/microbes association strategies for these two closely related Scleractinians sharing the same habitat, suggesting distinct sensitivity to environmental change.

Distinct Bacterial Microbiomes Associate with the Deep-Sea Coral Eguchipsammia fistula from the Red Sea and from Aquaria Settings

“…Studies on deep-sea corals are scarcer, but findings are similar and indicate that environmental conditions influence coral-associated bacterial communities. For instance, diet of deep-sea corals is thought to influence the coral microbiome (Neulinger et al, 2008;Meistertzheim et al, 2016) and in turn the microbiome can unlock nutrient resources for the holobiont (Middelburg et al, 2015). In this context, L. pertusa has been suggested to be a more opportunistic feeder (based on fatty acid and δ 15 N analyses) than M. oculata (Meistertzheim et al, 2016).…”

“…In this context, L. pertusa has been suggested to be a more opportunistic feeder (based on fatty acid and δ 15 N analyses) than M. oculata (Meistertzheim et al, 2016). This may be based on a more variable bacterial microbiome compared to M. oculata, which also aligns with a higher flexibility and phenotypic plasticity reflected by higher thermal tolerance and a larger distribution range (Neulinger et al, 2008;Meistertzheim et al, 2016). E. fistula possesses a wide distribution range including the Red Sea, Indo-Pacific, Australia, and New Zealand (van der Land, 2008).…”

“…In their natural habitat, E. fistula may host a highly diverse microbiome to utilize a wide range of nutrients. Moreover, the more diverse diet under in situ conditions may be a source of microbial diversity itself (sensu Meistertzheim et al, 2016), and certain microbiome members may proliferate in response to carbon sources that become episodically available. By comparison, ex situ coral specimens were reared under highly stable environmental conditions and provided with a uniform diet, where the less diverse microbiome may reflect the uniform diet or may be a direct consequence of it.…”

“…For instance, diet of deep-sea corals is thought to influence the coral microbiome (Neulinger et al, 2008;Meistertzheim et al, 2016) and in turn the microbiome can unlock nutrient resources for the holobiont (Middelburg et al, 2015). In this context, L. pertusa has been suggested to be a more opportunistic feeder (based on fatty acid and δ 15 N analyses) than M. oculata (Meistertzheim et al, 2016). This may be based on a more variable bacterial microbiome compared to M. oculata, which also aligns with a higher flexibility and phenotypic plasticity reflected by higher thermal tolerance and a larger distribution range (Neulinger et al, 2008;Meistertzheim et al, 2016).…”

“…However, mainly due to their limited accessibility, the knowledge on deep-sea corals is still scarce, especially in regard to their associated microbial communities. Few studies characterized deep-sea coral associated bacterial communities, focusing mainly on octocorals (Penn et al, 2006;Gray et al, 2011;Kellogg et al, 2016;Lawler et al, 2016) and two reef-building scleractinian corals, namely Lophelia pertusa and Madrepora oculata (Yakimov et al, 2006;Neulinger et al, 2008Neulinger et al, , 2009Hansson et al, 2009;Kellogg et al, 2009Kellogg et al, , 2017Schöttner et al, 2009Schöttner et al, , 2012Galkiewicz et al, 2011;Emblem et al, 2012;van Bleijswijk et al, 2015;Meistertzheim et al, 2016). Findings include species-specific microbiomes, but also considerable spatial and temporal variations.…”