Abstract
Sponges are abundant, diverse and functionally important organisms of coral reef ecosystems. Sponge-associated microorganisms have been receiving greater attention because of their significant contribution to sponge biomass, biogeochemical cycles and biotechnological potentials. However, our understanding of the sponge microbiome is limited to a few species of sponges from restricted geographical locations. Here, we report for the first time the bacterial diversity of two cohabiting sponges, viz. Cinachyra cavernosa and Haliclona pigmentifera, as well as that in the ambient water from the coral reef ecosystems of the Gulf of Mannar, located along the southeast coast of India. Two hundred and fifty two clones in the 16S rRNA gene library of these sponges were grouped into eight distinct phyla, of which four belonged to the core group that are associated only with sponges. Phylogenetic analysis of the core bacteria showed close affinity to other sponge-associated bacteria from different geographical locations. γ-Proteobacteria, Chloroflexi, Planctomycetes and Deferribacter were the core groups in C. cavernosa while β and δ-Proteobacteria performed this role in H. pigmentifera. We observed greater OTU diversity for C. cavernosa (Hǀ 2.07) compared to H. pigmentifera (Hǀ 1.97). UniFrac analysis confirmed the difference in bacterial diversity of the two sponge species and also between the sponges and the reef water (p<0.001). The results of our study restate the existence of a host driven force in shaping the sponge microbiome.
Highlights
Sponges are primitive members of the evolutionary tree, accounting for 8500 taxonomically validated species [1,2]
It was observed that C. cavernosa was attached on the surface of H. pigmentifera, and such an association is rarely reported in sponges and this would be very appropriate for studying the role of host driven forces in shaping sponge microbiome
Since no previous reports on bacterial diversity of C. cavernosa and H. pigmentifera are available for comparison, we could not assign any bacteria as species-specific to the two host sponge species studied
Summary
Sponges are primitive members of the evolutionary tree, accounting for 8500 taxonomically validated species [1,2]. Understanding the diversity of microorganisms associated with sponges is necessary to puzzle out the functioning of the complex coral reef ecosystem, especially in the energy coupling between the benthic and pelagic communities [8].To date, 12 candidate phyla and 2 archaeal lineages have been identified from sponges from the Mediterranean and Pacific regions [9],but little is known from the Indian waters. These phyla include Chloroflexi (formerly green non-sulfur bacteria), Acidobacteria, Actinobacteria, and α-, γ-, and δ-proteobacteria [9]. Studies on the community structure of sponge-associated bacteria from different geographical regions are essential in order to understand the ecological implications of sponge—microbe interactions
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