as a comparative model host for light organ symbiosis.

Functional studies of host-microbe interactions benefit from natural model systems that enable the exploration of molecular mechanisms at the host-microbe interface. Bioluminescent colonize the light organ of the Hawaiian bobtail squid, , and this binary model has enabled advances in understanding host-microbe communication, colonization specificity, biofilms, intraspecific competition, and quorum sensing. The hummingbird bobtail squid, can be generationally bred and maintained in lab settings and has had multiple genes deleted by CRISPR approaches. The prospect of expanding the utility of the light organ model system by producing multigenerational host lines led us to determine the extent to which the light organ symbiosis parallels known processes in . However, the nature of the light organ, including its microbial constituency and specificity for microbial partners, has not been examined. In this report, we isolated bacteria from animals and tank water. Assays of bacterial behaviors required in the host, as well as host responses to bacterial colonization, illustrate largely parallel phenotypes in and hatchlings. This study reveals to be a valuable comparative model to complement studies in .IMPORTANCEMicrobiome studies have been substantially advanced by model systems that enable functional interrogation of the roles of the partners and the molecular communication between those partners. The system has contributed foundational knowledge, revealing key roles for bacterial quorum sensing broadly and in animal hosts, for bacteria in stimulating animal development, for bacterial motility in accessing host sites, and for biofilm formation in development and specificity of an animal's microbiome. is a second bobtail squid host, and one that has recently been shown to be robust to laboratory husbandry and amenable to gene knockout. This study identifies as a strong symbiosis model host due to features that are conserved with those of , which will enable the extension of functional studies in bobtail squid symbioses.