The Colonization of E. scolopes by V. fischeri

A highly specific process
V. fischeri colonize the light organ of E. scolopes through a highly specialized process. Only v.fischeri bacteria are capable of populating the light organ of the squid. Other non-symbiotic bacteria can aggregate host mucus, but only v. fischeri can enter pores and ducts.

The "Winnowing"

Through the study of bacterial mutants, three major stages of symbiotic colonization have been identified. These stages include (i) initiation of the association (initiation), (ii) colonization to the high cell density achieved by the wild type (accommodation), and (iii) persistence at a high cell density (persistence)”(Visick and Skousof, 2000).

How does colonization occur?
Newly hatched juvenile squid draws bacteria from sea water into the mantel cavity with the help of specialized ciliated epithelia. The epithelium secretes a mucus, as a response to peptidoglycan, in which bacterial symbionts will become concentrated. The bacterial symbionts will then migrate to the pores on surface of light organ, down ducts, and into blind-ended crypts, where they multiply. "Full colonization of crypts sends development signal to host that results in regression of superficial epithelium" (McFall-Ngai,2008). The light organ is now in an "exclusive" state. This irreversible loss of epithelium is part of the squid morphogenesis, which is mediated by molecules released by symbionts, including lipid A component of LPS and tatrepeptide monomer of peptidogylcan" (Chun et al, 2008). In addition, microvilli of epithelial cells increase in density so host membrane surrounds surface of bacterial cells. Once the bacteria is thought to be high in density, they become luminous and lose their flagella(mcFall-Ngai, 2008). FlrA controls flagellar gene expression.

A study by Qin et al. categorized QsrP to be a novel periplasmic protein that plays a role in the ability of V. fischeri to colonize the squid Eurpyrmna scolopes.