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Project 10

Ecophysiology of a dominant microbial sponge symbiont

PhD position. Supervisors: Michael Wagner (UniVienna) and Thomas Schweder (UniGreifswald) (with input from Matthias Horn, UniVienna). Host: UniVienna. Secondment internship: UniGreifswald.

Rationale

Marine sponges contain an astonishing diversity of up to several hundred microbial symbionts per individual, which can comprise 40% of the animal body volume and whose functions are (with very few exceptions) unknown. Recent molecular diversity surveys including 16S rRNA tag 454 pyrosequencing revealed that the composition of these symbionts is strongly influenced by the host. In many sponges, the most abundant microbial symbiont is represented by less than 10% of the sequences in the respective gene libraries, massively complicating a functional characterization of sponge symbionts via metagenomic, metaproteomic and single cell isotope labelling approaches. An exception to this distribution pattern is the Great Barrier Reef sponge Ianthella basta that contains an uncultured gammaproteobacterial symbiont that makes up almost 50% of all 16S rRNA gene tags from this sponge. This gammaproteobacterial symbiont belongs to a closely related group of symbionts, which have also been detected in other sponges, in corals, and in the beard worm Oligobrachia mashikoi, but nothing is known about their metabolism and interactions with their hosts.

Objectives

The objective of the proposed PhD project is to understand the metabolism of the dominant but yet uncultured gammaproteobacterial symbiont of I. basta by examining its genome and proteome, and by specifically testing for selected functions using isotope labelled substrates. Detailed insights into the physiology of the symbiont will reveal (i) the functional importance of the symbiont for its host, (ii) metabolic interactions between host and symbiont, and (iii) will provide guidance for future targeted cultivation attempts of the symbiont.

Key methods

Biomass from I. basta will be available through a well-established collaboration with Dr. Nicole Webster (Townsville, Australia). Density gradient centrifugation will be applied for further symbiont enrichment from the sponge. Enriched biomass will be used for metagenomics and metaproteomics. Based on these data specific hypothesis regarding the metabolic potential of the symbiont will be inferred and experimentally tested using single cell stable isotope probing with Raman microspectroscopy and NanoSIMS. For this purpose, sponges will be incubated by our collaboration partner with isotope-labelled substrates in aquaria under defined conditions.