This new study identified genes in the microbiome (bacteria, fungi, viruses) of certain types of corals that may play a role in how reefs respond to heat stress. "Prolonged exposure to heat can cause ‘bleaching' in which photosymbionts (symbiotic algae) are jettisoned from the coral animal, causing the animal to die. We found that when some corals become heat stressed, their microbiomes can protect them from bleaching," explained Monica Medina, professor of biology at Penn State and co-author of the work.
The corals analyzed were collected near Puerto Morelos, Mexico. The researchers focused on three species: mountainous star coral (Orbicella faveolata), knobby brain coral (Pseudodiploria clivosa) and the shallow-water starlet coral (Siderastrea radians). Each of them has a different sensitivity to thermal stress.
The objective was to study the relationship between the overall ability of corals to withstand thermal stress and differences in gene expression patterns related to these metabolic activities. In the case of corals, this process is highly influenced by photosymbionts as they provide at least 90% of the coral animals' energy needs through photosynthesis. But, the scientists who led the work have extended their research to the whole organism of corals, called "holobiont," which includes coral animal, photosymbiont and microbiome.
The researchers conducted an experiment in which the three coral species were kept in a tank for nine days at 34˚C, about 6°C higher than their natural environment. The scientists then sequenced the RNA of the holobionts to study their metabolic activities.