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Project 12

Transmission of symbionts in gutless marine oligochaetes

PhD position. Supervisors: Nicole Dubilier (MPIMM) and Olivier Gros (UniAntilles) with input from Jillian Petersen (MPIMM). Host: MPIMM. Secondment internship: to UniAntilles.

Rationale

Gutless oligochaetes are an unusual group of marine worms that harbor a highly specific consortium of endosymbiotic bacteria. These symbioses have not only led to the complete reduction of the worm's digestive system but also enabled them to live without an excretory system, an adaptation not known from any other animal hosts. Very little is known about how the symbionts are passed on from one generation to the next in gutless oligochaetes. Genomic analyses suggest that some of the symbionts may be transmitted vertically and others horizontally, but this has not been examined directly in morphological analyses.

Objectives

The objective of the proposed PhD project is to understand how the symbionts of gutless oligochaetes are transmitted from one generation to the next by i) examining eggs, embryos, juvenile stages, and sexually mature adult stages of the host for symbionts, and ii) the habitat of the worms for free-living stages of the symbionts. Field analyses (collection and preparation of hosts and environmental samples), cultivation of worms and attempts to raise aposymbiotic juveniles will be conducted at the UniAntilles which provides lab facilities with direct access to sampling in the coral reef sediments where the worms occur. A better knowledge of symbiont transmission will reveal how these symbioses are established and how different acquisition modes could have influenced the genomic evolution of the symbionts.

Key methods

PCR-based analyses of key genes (16S rRNA, ITS) and high-throughput 454 sequencing for symbiont identification combined with fluorescence in situ hybridization for confirmation and in-depth morphological and ontogenetic analyses, as well as Raman microscopy and NanoSIMS to analyse at which stage the symbionts become metabolically active.