Bacterial Communities Associated With Healthy and Diseased (Skeletal Growth Anomaly) Reef Coral Acropora cytherea From Palk Bay, India

Raju Rajasabapathy,Kesava Priyan Ramasamy,Chellandi Mohandass,Rathinam Arthur James,Balakrishnan Manikandan

doi:10.3389/fmars.2020.00092

Raju Rajasabapathy, Kesava Priyan Ramasamy + Show 3 more

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https://doi.org/10.3389/fmars.2020.00092

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Abstract

Skeletal growth anomalies (SGA) are easily recognizable disease in reef-forming corals which drain energy from the host and end up with mortality. We collected mucus samples of healthy and SGA affected colonies of Acropora cytherea from Palk Bay, the southeast coast of India and investigated the taxonomic composition of mucus-associated bacterial communities using full-length 16S rRNA gene nanopore sequencing. Metagenomic analysis revealed the dominance of Proteobacteria, Firmicutes and Actinobacteria in both healthy and diseased samples. The proportion of Proteobacteria in diseased samples was almost doubled compared to the healthy one, whereas Acidobacteria (fourth dominant phyla in healthy sample) and Actinobacteria were significantly low in diseased samples. Planctomycetes, Cyanobacteria and Chloroflexi were some of the other major phyla found in healthy samples which were low in diseased corals. Kruskal-Wallis test indicated high number of putative pathogenic bacteria group viz. Staphylococcus, Salmonella, Klebsiella and Escherichia in diseased samples compared to healthy coral. The corals perhaps have acquired potential pathogens belong to the phylum Proteobacteria during SGA formation.

Highlights

Coral diseases become a rising issue over several decades, yet fundamental knowledge of their causes is not known in many cases
This study provides detailed amplicon metagenomic analysis into the coral mucus associated bacterial communities based on 16S rRNA gene of the healthy and diseased coral A. cytherea
We established that the bacterial community structure is greatly varied between healthy and Skeletal growth anomalies (SGA) affected corals and found Proteobacteria groups were the major contributor to these variations

Summary

Introduction

Coral diseases become a rising issue over several decades, yet fundamental knowledge of their causes is not known in many cases. Skeletal growth anomalies (SGAs) are a group of coral diseases characterized by reduced colony growth, absence of polyp formation, decreased skeleton density and reduced numbers of zooxanthellae (Cheney, 1975; Bak, 1983) and sources confirm that SGAs are not transmissible (Peters et al, 1986). SGA on coral reefs was first witnessed in Madrepora kauaiensis from Hawaii (Squires, 1965) since it has been reported in several. Though the etiology of many coral diseases remains unknown, majority of the diseases reported are recognized or suspected to be of microbial origin (Richardson and Aronson, 2002). Previous studies on reef coral Acropora cytherea revealed that the formation of SGA is potentially intensified by environmental stresses such as increased sea temperature (Irikawa et al, 2011). While hitherto no report of microbial community variations from healthy and SGA affected A. cytherea are available

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