Coral microbiota: temperature and your inhibition

It has been found that there are bacteria which colonise the coral mucus layer and can act as a barrier to pathogenic colonisation. This is thought to be because of the bacteria-bacteria interactions between the pathogens and the microbiota associated with the corals. Previous studies have already found that bacteria which are attached to some form of surface are more likely to produce antibiotics than bacteria which are free living within the water column. The authors of this study have outlined that many of the bacteria associated with corals are closely related to bacteria which produce antibiotics.  

The authors of this study outline the need for study within the topic of antagonistic interactions between pathogens and the associated bacteria of the coral Montastrea annularis, and the relationships between rising sea temperatures and coral disease. This study found that antagonistic interactions were fairly common although it is noted that each individual isolate was only inhibited by a few other isolates. This suggests that each isolate has a specific other type or types of bacteria which it can inhibit and be inhibited by. The isolates themselves were predominantly α-proteobacteria and γ-proteobacteria, within the γ-proteobacteria the most common genera were Vibrionales and Alteromonadales. When subjected to temperatures of 25°C the data collected showed that most bacteria would show sensitivity to inhibition to at least on other bacterium. However, at temperatures of 31°C more bacteria were able to grow unchecked. Though there are indications that the bacteria which can be agonistic have the ability to inhibit the growth of other bacteria at both 25°C and 31°C.

An observation noted by the authors was that there was a group of γ-proteobacteria were far more specific in their inhibition as they primarily targeted α-proteobacteria. This could mean that these microbes have co-evolved together to produce an antibiotic that can only target the α-proteobacteria or it could mean that other bacteria have evolved mechanisms which render the antibiotic ineffective against them leaving the α-proteobacteria the only bacteria still sensitive to the particular antibiotic produced.

This does not bode well for coral populations in the future if sea temperatures continue to rise as it means that the inhibition of bacteria is lessened and therefore increases the chances of the coral protracting diseases such as black band or white pox disease.

The authors have stated the need for techniques to investigate this in situ to be developed so that we can more accurately understand how the antagonistic interactions in the microbial communities associated with the corals work. Further research also needs to be done in regards to the interactions of the nutrient availability, predation and the competitive interactions of the community so that we can achieve a more full appreciation for the ecology of Scleractinian corals and their associated microbiota.

Rypien Kl., Ward JR., Azam F., 2010, Antagonistic interactions among coral-associated bacteria, Environmental Microbiology, 12, 28-39