Coral-associated micro-organisms and their roles in promoting coral health and thwarting diseases

Abstract

Over the last decade, significant advances have been made in characterization of the coral microbiota. Shifts in its composition often correlate with the appearance of signs of diseases and/or bleaching, thus suggesting a link between microbes, coral health and stability of reef ecosystems. The understanding of interactions in coral-associated microbiota is informed by the on-going characterization of other microbiomes, which suggest that metabolic pathways and functional capabilities define the 'core' microbiota more accurately than the taxonomic diversity of its members. Consistent with this hypothesis, there does not appear to be a consensus on the specificity in the interactions of corals with microbial commensals, even though recent studies report potentially beneficial functions of the coral-associated bacteria. They cycle sulphur, fix nitrogen, produce antimicrobial compounds, inhibit cell-to-cell signalling and disrupt virulence in opportunistic pathogens. While their beneficial functions have been documented, it is not certain whether or how these microbes are selected by the hosts. Therefore, understanding the role of innate immunity, signal and nutrient exchange in the establishment of coral microbiota and in controlling its functions will probably reveal ancient, evolutionarily conserved mechanisms that dictate the outcomes of host-microbial interactions, and impact the resilience of the host.

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

“…This notion is supported by recent studies that show, at least in part, flexible bacterial microbiomes of the coral holobiont to environmental change (Jessen et al, 2013;Roder et al, 2015;Hernandez-Agreda et al, 2016;Röthig et al, 2016;Ziegler et al, 2016Ziegler et al, , 2017. However, our knowledge on the role of the bacterial microbiome to coral holobiont function is still limited (Bourne and Webster, 2013;Bourne et al, 2016), although bacteria are shown to contribute to coral health (Rosenberg et al, 2007;Krediet et al, 2013) and are involved in nutrient cycling (Rädecker et al, 2015;Bourne et al, 2016).…”

Evidence for rapid, tide-related shifts in the microbiome of the coral Coelastrea aspera

“…If the 'core' biome is disrupted, for example during periods of stress, 'transient' microbiota may then be able to establish and increase in abundance, albeit temporarily. Such transitions may mark a key moment when normally transient potentially pathogenic organisms become established and diseases begin to manifest themselves (Cho and Blaser 2012;Krediet et al 2013). Indeed, such shifts are routinely noted in the majority of studies assessing the microbiota of both healthy and diseased coral tissues at any given time (reviewed in Bourne et al 2009).…”

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

“…However, having a variable, environmentally-adapted microbiota does not exclude having also a core, obligate symbiotic microbiota present in the same coral species independently of geographical location and/or environmental conditions experienced (Kooperman et al, 2007;Chen et al, 2010). While the discussion on the species-vs. sitespecific coral microbiota has so far been focused on their genetic identity, it has been also proposed that specificity may rather lay on bacterial functional diversity (Krediet et al, 2013). Molecular biology methods in the past decades have provided invaluable insights into the diversity of coral's microbiota, but only recently genomics approaches have started revealing which functional traits lay behind the genetic identity of the microbes inhabiting the coral holobiont.…”

“…Coral-associated bacteria can either damage the animal host by causing disease (Rosenberg and Ben Haim, 2002;Krediet et al, 2013), or provide benefits via antibiotic production and substrate acquisition facilitation . Coralassociated bacteria have been found to perform various metabolic functions, including having a role in carbon, phosphorus, sulfur and nitrogen cycles (Thurber et al, 2009;Kimes et al, 2010Kimes et al, , 2013Mouchka et al, 2010).…”

“…Environmental stress factors such as bleaching, thermal stress, irradiance, disease or changes in organic matter may disrupt the symbiotic relationships of the coral holobiont, often resulting in a change of the coral-associated microbiota genetic and/or functional diversity (Ritchie and Smith, 1995;Kline et al, 2006;Smith et al, 2006;Thurber et al, 2009;Krediet et al, 2013). This change can be either direct (the environment affects the microbiota) or indirect (the environment affects the coral host physiology, which in turn forces a change in its associated microbiota Ritchie, 2006;Mouchka et al, 2010).…”