The Microbial Ecology of Marine Sponges: Biogeography to Genes

Abstract

Marine sponges (Porifera) are among the most ancient Metazoa and are known for their close association with microorganisms. The symbiosis between marine sponges and bacteria and archaea has been relatively well studied, as many of these symbionts produce biologically active secondary metabolites, valuable for biotechnology and drug applications. A less well characterised group of symbionts in marine sponges is the microbial eukaryotes, including organisms such as diatoms, dinoflagellates and fungi. Microbial eukaryotes are influential members of marine food webs and are also of symbiotic importance to marine organisms such as corals. They are likely to play an important role in marine sponges. The first aim of my project was to determine patterns of microbial eukaryote community composition in marine sponges in relation to geographic location using denaturing gradient gel electrophoresis. Due to the divergence of the sponge 18S ribosomal RNA gene (rRNA), the selected primer pairs were only successful in amplifying sponge DNA and revealed no information regarding microbial eukaryotes, and thus I concluded that using ‘universal’ 18S rRNA-targeting primers is not appropriate for investigating the diversity of microbial eukaryotes within marine sponges. The second aim of my project was to investigate the microbial community of Tethya stolonifera, a small sponge common to northeastern New Zealand. A recent study indicated that the bacterial community of this sponge is consistently dominated (78% of obtained 16S rRNA sequences) by a single member of the Betaproteobacteria. Using metagenomics and fluorescence in situ hybridisation (FISH) I aimed to (1) determine whether 16S rRNA-targeted pyrosequencing had provided an accurate insight into the bacterial community composition of T. stolonifera, and (2) to reveal the metabolic capabilities of the as yet uncultured betaproteobacterium. The results of this study indicate that 16S rRNA-targeted community analysis resulted in a slight over representation of Betaproteobacteria when compared to metagenomic and FISH results. The genes assigned to Betaproteobacteria through MEGAN analysis are consistent with genes belonging to other bacterial sponge symbionts and reveal a snapshot of what this bacterium is capable of.