Microbial Regulation in Gorgonian Corals

Abstract

Gorgonian corals possess many novel natural products that could potentially mediate coral-bacterial interactions. Since many bacteria use quorum sensing (QS) signals to facilitate colonization of host organisms, regulation of prokaryotic cell-to-cell communication may represent an important bacterial control mechanism. In the present study, we examined extracts of twelve species of Caribbean gorgonian corals, for mechanisms that regulate microbial colonization, such as antibacterial activity and QS regulatory activity. Ethanol extracts of gorgonians collected from Puerto Rico and the Florida Keys showed a range of both antibacterial and QS activities using a specific Pseudomonas aeruginosa QS reporter, sensitive to long chain AHLs and a short chain N-acylhomoserine lactones (AHL) biosensor, Chromobacterium violaceium. Overall, the gorgonian corals had higher antimicrobial activity against non-marine strains when compared to marine strains. Pseudopterogorgia americana, Pseusopterogorgia acerosa, and Pseudoplexuara flexuosa had the highest QS inhibitory effect. Interestingly, Pseudoplexuara porosa extracts stimulated QS activity with a striking 17-fold increase in signal. The stimulation of QS by P. porosa or other elements of the holobiont may encourage colonization or recruitment of specific microbial species. Overall, these results suggest the presence of novel stimulatory QS, inhibitory QS and bactericidal compounds in gorgonian corals. A better understanding of these compounds may reveal insight into coral-microbial ecology and whether a therapeutic potential exists.

Quorum Sensing Interference and Structural Variation of Quorum Sensing Mimics in Australian Soft Coral

“…The widespread prevalence of QS inhibition as well as the presence of QS induction in the soft corals screened here is consistent with QS activity found across a range of marine invertebrates (Taylor et al, 2004;Skindersoe et al, 2008;Hunt et al, 2012). The dual presence of induction and inhibition of QS is similar to that found previously in gorgonian coral extracts (Hunt et al, 2012) but contrasts with the sole QS inhibition activity that was identified in D. pulchra (Kjelleberg et al, 1997). QS induction was also established in extracts of marine sponges and sponge associated bacteria (Taylor et al, 2004).…”

“…Widespread QS inhibitory activity has been observed to occur in the marine benthos, particularly in sponges and soft corals (Taylor et al, 2004;Skindersoe et al, 2008;Hunt et al, 2012). Soft corals contain a number of secondary metabolites with the structural potential to mimic QS, including furanocembrenes (cembranoid diterpenes with fused 5-membered ether rings) and cembranolides (cembranoids that possess a fused second ring in the form of a lactone).…”

Variability in Microbial Community Composition and Function Between Different Niches Within a Coral Reef

“…The high abundance of regulation and cell signalling genes in the coral seawater niches suggests that the microbial community associated with corals engages in higher levels of cell-cell communication than what occurs in open water niches. Regulation and cell signalling are likely to be important functions on coral reefs, where bacteria may use signalling processes, including quorum sensing, to organise cellular functions to colonise host organisms including corals and sponges [97][98][99][100]. Chemical signalling also potentially allows bacteria to defend the holobiont from invading pathogens by altering behaviours such as swarming, biofilm formation and the production of anti-microbial compounds [97,98,[100][101][102][103][104].…”

“…Chemical signalling also potentially allows bacteria to defend the holobiont from invading pathogens by altering behaviours such as swarming, biofilm formation and the production of anti-microbial compounds [97,98,[100][101][102][103][104]. On the other hand, quorum sensing can regulate virulence in some bacteria [103], which could enable pathogens to more readily infect the host and outcompete beneficial microbes [100,104]. The elevated occurrence of regulation and cell signalling genes in the coral seawater niches indicates that these processes, which will affect the interactions between microbes and the coral host, are particularly important in the coral holobiont.…”

“…Regulation and cell signalling are likely to be important functions on coral reefs, where bacteria may use signalling processes, including quorum sensing, to organise cellular functions to colonise host organisms including corals and sponges [97][98][99][100]. Chemical signalling also potentially allows bacteria to defend the holobiont from invading pathogens by altering behaviours such as swarming, biofilm formation and the production of anti-microbial compounds [97,98,[100][101][102][103][104]. On the other hand, quorum sensing can regulate virulence in some bacteria [103], which could enable pathogens to more readily infect the host and outcompete beneficial microbes [100,104].…”