Speaker
Description
Nutritional symbioses between chemosynthetic bacteria and animals form the base of the food web at hydrothermal vent ecosystems. Deep-sea mussels are among the most successful host groups in these ecosystems, and many species harbor sulfur-oxidizing (SOX) bacteria. We discovered that SOX symbionts in deep-sea mussels differ in their morphology: some mussels have endosymbionts, while others have ectosymbionts. Endosymbionts live inside specialized gill cells, whereas ectosymbionts colonize the surfaces of gill cells. Our study examined how these lifestyles influence the metabolic potential and strain diversity of SOX symbionts in five mussel species. We found no significant differences between endo- and ectosymbionts in genome size, GC content, or central metabolic pathways. The only notable difference was the higher strain diversity of ectosymbionts, with four times higher single nucleotide variants in ectosymbionts compared to endosymbionts. This higher strain diversity could be shaped by relaxed host selectivity in ectosymbiotic associations, or the ectosymbionts' exposure to more heterogeneous environments compared to the relatively stable environment inside host cells. Ongoing analyses of symbiont population sizes and the influence of selection on genes (pN/pS) aim to elucidate the processes shaping the genetic diversity of ectosymbionts.
