Metagenomic sequencing reveals altered bacterial abundance during coral-sponge interaction: Insights into the invasive process of coral-killing sponge Terpios hoshinota.

The coral-killing invasive sponge, Terpios hoshinota, causes extensive mortality to live corals and is a potential threat to reefs at different geographical locations. However, to date, the invasive mechanism remains largely unknown. In this study, we aimed to understand the bacterial competition between sponge and coral hosted bacteria when sponge outcompetes corals. We analysed the bacterial community of Terpios-invaded coral tissue, and the adjacent healthy tissue of sponge-invaded Favites colonies from Palk bay reef (South East Asia) of the Indian Ocean by using next-generation sequencing. Comparative analysis revealed similar bacterial diversity in both healthy and sponge covered coral tissues. However, relative abundance found to be differed between the groups. Terpios covered coral tissue had higher bacterial abundance than the healthy coral tissue. Bacterial phyla such as Bacteroidetes, Proteobacteria, Firmicutes, Actinobacteria, and Verrucomicrobia live both in sponge covered and healthy coral tissue. Notably, many of the lower abundant bacteria in healthy coral tissue (abundance <1%) became the most abundant in sponge-invaded tissue. In particular, the genus Neisseria, Bacteroides, and members of Pseudoalteromonas predominant in sponge-invaded tissue. Similar bacterial diversity between normal and and sponge-invaded coral tissues suggest that bacteria follow an exploitative competition, which might favoured sponge growth over corals.