Abstract
The recognition of the microbiota complexity and their role in the evolution of their host is leading to the popularization of the holobiont concept. However, the coral holobiont (host and its microbiota) is still enigmatic and unclear. Here, we explore the complex relations between different holobiont members of a mesophotic coral Euphyllia paradivisa. We subjected two lines of the coral—with photosymbionts, and without photosymbionts (apo-symbiotic)—to increasing temperatures and to antibiotics. The different symbiotic states were characterized using transcriptomics, microbiology and physiology techniques. The bacterial community’s composition is dominated by bacteroidetes, alphaproteobacteria, and gammaproteobacteria, but is dependent upon the symbiont state, colony, temperature treatment, and antibiotic exposure. Overall, the most important parameter determining the response was whether the coral was a symbiont/apo-symbiotic, while the colony and bacterial composition were secondary factors. Enrichment Gene Ontology analysis of coral host’s differentially expressed genes demonstrated the cellular differences between symbiotic and apo-symbiotic samples. Our results demonstrate the significance of each component of the holobiont consortium and imply a coherent link between them, which dramatically impacts the molecular and cellular processes of the coral host, which possibly affect its fitness, particularly under environmental stress.
Highlights
A holobiont is defined as the combination of all organisms that compose a specific system and combine their adaptations to meet environmental challenges as a consortium
The symbiosis effect was tested by creating apo-symbiotic corals as described above
This study is novel in dissecting how can environmental changes such as short-term heat stress affect the whole holobiont and its components; we characterize the response of three components of the coral holobiont—the coral host, the photosynthetic algae, and the associated bacteria—and show how each of them may influence each other
Summary
A holobiont is defined as the combination of all organisms that compose a specific system and combine their adaptations to meet environmental challenges as a consortium. The study of corals has begun to take a holobiont approach, in which the animal host is examined together with its associated diverse microbial community that includes bacteria, archaea, fungi, protists and viruses [6,7]. Despite an appreciation that interactions between corals and associated microbes are likely to have a dramatic influence on coral physiology and health [8], our understanding of the role and the crosstalk between the microbiota and its host is still limited. Many studies have focused on coral–pathogen interactions [9,10], beneficial symbioses, such as the delivery of photosynthesis products from symbiotic algae [11], resistance to pathogens [12], and nitrogen fixation [13], have been described
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