Up to now, the study of bacterial reproduction focused on model organisms. On the other hand, cell biological research on environmental bacteria - including those thriving on animal surfaces - are scarce. A single layer of Gammaproteobacteria (Candidatus genus Thiosymbion) coats the surface of free-living marine nematodes (Stilbonematinae). The spatial dispositions of the bacterial symbionts on the surface of their cognate hosts is species-specific, invariable, and mediated by extraordinary reproductive strategies. We seek to understand the molecular mechanisms of the latter and why they evolved.