Project description:Endozoicomonas are prevalent, abundant bacterial associates of marine animal hosts, including corals. Their role in holobiont health and functioning, however, remains poorly understood. To identify putative interactions within the coral holobiont, we characterized a novel Endozoicomonas isolate and assessed its transcriptomic and proteomic responses to tissue extracts of its native host, the Red Sea coral Acropora humilis, at control and elevated temperatures. We show that host cues stimulated differential expression of genes assumed to be involved in the modulation of the host immune response by Endozoicomonas, such as flagellar assembly genes, ankyrins, ephrins, and serpins. Proteome analysis revealed the upregulation of vitamin B1 and B6 biosynthetic as well as glycolytic processes by Endozoicomonas in response to host cues. We further demonstrate that the inoculation of A. humilis with its native Endozoicomonas strain resulted in enhanced holobiont health metrics, such as host tissue protein content and algal symbiont photosynthetic efficiency. Behavioral, physiological, and metabolic changes in Endozoicomonas may be key to the onset and function of mutualistic interactions within the coral holobiont, and our results suggest that the priming of Endozoicomonas to a symbiotic lifestyle may involve modulation of host immunity and the exchange of essential metabolites with other holobiont members. Consequently, Endozoicomonas presumably plays an important role in holobiont nutrient cycling and may therefore be implicated in its health, acclimatization, and ecological adaptation.
Project description:Purpose: Corals are major sources of dimethylsulphoniopropionate (DMSP), a compound that plays a central role in the global sulphur cycle. While DMSP biosynthesis pathways have been investigated in plants and algae, the molecular basis for its production by corals is unknown. Given its potential role as an osmolyte, the effect of salinity stress on levels of DMSP was investigated in both adults and juveniles (lacking photosynthetic symbionts) of the coral Acropora millepora. This study used transcriptomic data to analyse the effects of salinity over the coral A. millepora and to identify coral genes likely to be involved in DMSP biosynthesis. Methods: Adults coral transcriptomic libraries were constructed from samples exposed during 1 and 24 hours of salinity treatment (25 PSU) and control (35 PSU) conditions (n=5 per condition). Juveniles coral transcriptomic libraries were constructed from samples exposed to 24 and 48 hours of salinity treatment (28 PSU) and control (35 PSU) conditions (n=6 per condition). All libraries were sequenced by 100 bp paired-end in a HiSeq 2000. Reads were mapped onto the Acropora millepora genome using TopHat2 to produce a count data gene expression matrix for subsequent gene expression analysis using DESeq2 package. Results: In adult coral samples, 5.5 - 10.2 million RNAseq reads were obtained for each treatment sampling time while 3.4 - 8.8 million reads were obtained for each juvenile coral sample. The count matrix of the 26,622 A. millepora gene predictions were generated using htseq-count workflow. BlastP analysis of the A. millepora gene predictions led to the identification of coral members of gene families implicated in DMSP biosynthesis in other organisms, while RNA-seq data was used to identify the differentially expressed ones in response to hyposaline stress and on this basis were considered to be candidates for roles in DMSP biosynthesis in corals. Conclusions: Hyposaline stress increased DMSP production in both adults and aposymbiotic juvenile corals, and transcriptomic analyses highlighted the potential involvement of specific candidate genes in the production of DMSP via an alga-like pathway. The biochemistry of DMSP production is not well established for any eukaryotic system and, as the first animals in which it has been demonstrated, this is particularly true in the case of corals. Our RNA-seq results enabled the identification of candidates for roles in DMSP biosynthesis in corals but, given its critical roles in diverse biological processes, a thorough investigation of the molecular mechanisms leading to its production by corals is required.