Abstract
Endozoicomonadaceae bacteria are found in association with marine organisms across ocean ecosystems. Interactions may range from mutualistic to parasitic depending on host species and ecological context. Their genomic repertoire suggests metabolic versatility and capacity for rapid adaptation and transitioning between free-living and host-associated lifestyles. Some lineages, however, undergo genome reduction, are host-specific, and lack cultivability. Here we present an advanced genomic perspective and updated view on the functional diversity of Endozoicomonadaceae along the mutualism-parasitism continuum. We discuss their roles in marine symbioses, potential for microbiome engineering, and highlight knowledge gaps of their ecology to be addressed in future research.