LEECHSYMBIO · The Mexican leech Haementeria officinalis and its nutritional symbiont as a model system for the study of strict blood-feeding animal-microbe symbioses and bacteriocyte development

Strict blood-feeding leeches are confronted with a strong B-vitamin deficiency and thus rely on bacterial symbionts to supplement their unbalanced diet. Recent evidence showed that the Mexican leech Haementeria officinalis houses in a distinct specialised organ intracellular Providencia siddallii symbionts, which have a highly reduced genome but maintained genes required for B vitamin biosynthesis. The aim of this proposal is to establish this leech as a model system for studying the intricacies of nutritional blood-feeding symbioses. The genomes of Providencia symbionts of 4 additional Haementeria species will be sequenced and analysed to identify core-metabolic pathways and to reconstruct the evolutionary history of this symbiosis. A draft genome sequence of the Mexican leech Ha. officinalis will be determined, providing unique insights into metabolic complementarity. Comparison with the available genome of the related non-blood-feeding leech Helobdella robusta will facilitate identification of genomic determinants of the acquisition/loss of the bacteriome and the blood feeding habit. Bacteriome development and colonization will be investigated using different developmental stages and advanced microscopy techniques. Host control and nutritional role of the symbiont will be studied using isotope probing experiments and state-of-the-art chemical imaging and metabolomics methods. This project will provide comprehensive insights into a nutritional symbiosis in medically relevant blood-feeding animals, including the evolution of specialised symbiosis organs and metabolic interactions between both partners. It will bring together a postdoc with a strong background in bioinformatics and bacterial symbionts with a host lab focused on experimental and molecular analysis of microbe-host interactions. This set-up ensures both an ideal environment for the postdoc on his way to an truly independent researcher, and an efficient two-way transfer of knowledge.