Photosynthetic symbionts influence the microbiome associated with coral reef invertebrates
Coral reefs are home to a diverse array of invertebrate species hosting a wide range of symbiotic micro-organisms. It has been well documented that photosynthetic symbionts such as Symbiodinium spp dinoflagellates, live within tropical coral host species and not only benefit the host by providing vital nutrition, but also impart important services to the ecosystem. Their contribution to primary productivity, mineral recycling and release of complex carbon-containing exudates combine to make coral reefs one of the most diverse habitats on the planet. Whilst microbial diversity and function has been well documented in coral and sponge species, the authors identified a lack of data in other taxa commonly found on reefs.
This study used 16s rRNA gene amplicon pyrosequencing in order to characterise the microbiomes of 16 commonly found marine invertebrates on the Great Barrier Reef, spreading over 5 taxa. This method allows inexpensive, rapid gene sequencing for metagenomic analysis and uses PCR amplification, relying on detection of pyrophosphate release (and resultant light emitted after several further reactions) when a complimentary nucleotide is incorporated.
Data analysis showed that invertebrates hosting photosynthetic symbionts were dominated by Gammaproteobacteria classes whereas the invertebrate hosts without any photosynthetic symbionts present tended to have a higher abundance of Alphaproteobacteria. Furthermore, microbial composition differed between invertebrate groups, explained in part by the presence of photosynthetic symbionts. It is clear that the presence of photosynthetic symbionts had a significant influence on the composition of the host invertebrate microbiome. The invertebrate species that hosted photosynthetic symbionts, correlated highly to the presence of bacterial species that are important in the metabolisation of dimethylsulfoniopropionate (DMSP) to dimethylsulphide (DMS) which, in its aerosol form, is paramount in cloud condensation nuclei (CCN) formation and climate regulation. Coral reefs are reported to be one of the major contributors to DMSP production, believed to be derived from marine invertebrate symbiotic dinoflagellates.
The authors have shown that presence of photosynthetic symbionts may be paramount in the structuring and organisation of the marine invertebrate holobiont and further research in this area may contribute to our knowledge of reef microbial relationships and implications, with particular importance attributed to DMS production and the prospect of global warming. If, as these authors are suggesting, the photosynthetic symbionts play a role in structuring the microbiome of their invertebrate hosts, this may also have a bearing on their expulsion during times of thermal stress. With climate change high on many research council agendas, understanding these complex microbial relationships may give some insight into climate regulation and impacts associated with warming seas.
Bourne, D. G., Dennis, P. G., Uthicke, S., Soo, R. M., Tyson, G. W., & Webster, N. (2013). Coral reef invertebrate microbiomes correlate with the presence of photosymbionts. ISME 7, 1452-1458