Microbial diversity in the coralline sponge Vaceletia crypta.

Coralline sponges of the genus Vaceletia are regarded as 'living fossils', the only recent members of the so-called 'sphinctozoan-type' sponges that contributed to reef-building during the Palaeozoic and Mesozoic eras. Vaceletia species were thought to be extinct until the discovery of Vaceletia crypta in the 1970s. Here, we used molecular methods to provide first insights into the microbial diversity of these coralline sponges. Both denaturing gradient gel electrophoresis (DGGE) analyses of 19 Vaceletia specimens and the analysis of 427 clones from a bacterial 16S rRNA gene clone library of a specimen of V. crypta from the Great Barrier Reef (Australia) revealed high diversity and a complex composition with a relatively uniform phylogenetic distribution. Only a single archaeal 16S rRNA phylotype was recovered. The most abundant bacteria were the Chloroflexi (35 %). Of the microbial community, 58 % consisted of the Gammaproteobacteria, Gemmatimonadetes, Actinobacteria, Nitrospira, Deltaproteobacteria, Deferribacteres and Acidobacteria, with nearly equal representation. Less abundant members of the microbial community belonged to the Alphaproteobacteria (3 %), as well as to the Poribacteria, Betaproteobacteria, Cyanobacteria, Spirochaetes, Bacteroidetes, Deinococcus-Thermus and Archaea (all together 4 %). Of the established 96 OTUs, 88 % were closely related to other sponge-derived sequences and thereof 71 OTUs fell into sponge- or sponge-coral specific clusters, which underscores that the "living fossil" coralline sponge Vaceletia shares features of its microbial community with other sponges. The DGGE cluster analysis indicated distinct microbial communities in the different growth forms (solitary and colonial) of Vaceletia species.