Abstract
Marine sponges are sources of various bioactive metabolites, including several anticancer drugs, produced mainly by sponge-associated microbes. Palk Bay, on the south-east coast of India, is an understudied, highly disturbed reef environment exposed to various anthropogenic and climatic stresses. In recent years, Palk Bay suffered from pollution due to the dumping of untreated domestic sewage, effluents from coastal aquaculture, tourism, salt pans, cultivation of exotic seaweeds, and geogenic heavy-metal pollution, especially arsenic, mercury, cadmium, and lead. Low microbial-abundant sponge species, such as Gelliodes pumila and Cliona lobata, were found to be ubiquitously present in this reef environment. Triplicate samples of each of these sponge species were subjected to Illumina MiSeq sequencing using V3–V4 region-specific primers. In both C. lobata and G. pumila, there was an overwhelming dominance (98 and 99%) of phylum Candidatus Saccharibacteria and Proteobacteria, respectively. The overall number of operational taxonomic units (OTUs) was 68 (40 and 13 OTUs unique to G. pumila and C. lobata, respectively; 15 shared OTUs). Alphaproteobacteria was the most abundant class in both the sponge species. Unclassified species of phylum Candidatus Saccharibacteria from C. lobata and Chelotivorans composti from G. pumila were the most abundant bacterial species. The predominance of Alphaproteobacteria also revealed the occurrence of various xenobiotic-degrading, surfactant-producing bacterial genera in both the sponge species, indirectly indicating the possible polluted reef status of Palk Bay. Studies on sponge microbiomes at various understudied geographical locations might be helpful in predicting the status of reef environments.
Highlights
Sponges are sessile filter feeders and are regarded as holobionts, which comprise 35–40% of microbial communities in their mesohyl[1,2,3]
Two sponge species collected from Palk Bay for this study were found to be Gelloides pumila (Lendenfeld, 1887) and Cliona lobata (Hancock, 1849) based on the morphology and spicule structures
Sponges act as filters of reef environments by capturing various planktonic organisms, including microbes[6,16]
Summary
Sponges (phylum: Porifera) are sessile filter feeders and are regarded as holobionts, which comprise 35–40% of microbial communities in their mesohyl[1,2,3]. Sponges are considered to have been in association with microbes since the Precambrian period, and this relationship has immensely helped the ecological succession of this ancient metazoan This relationship is considered to be transient because the inflow of seawater into the sponge tissues does not allow any particular community of bacteria to remain stagnant (via filter-feeding activity). Studies on sponge microbial communities are important for predicting the health of s ponges[11] in a particular environment as they directly represent the specific type of microbes present during the sampling period (indicative of polluted sites or dumpsites). This study attempts to report the bacterial diversity of two commonly available sponge species in the highly disturbed reefs of Palk Bay, on the south-east coast of India, through a comprehensive 16S rRNA metagenomic analysis and highlights the abundance of different bacterial phyla, especially the class Alphaproteobacteria, and their contribution to the sustainability of these two sponge species
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