Fig. 1

Overview of symbiotic host tissue—development of the squid light organ and key sites for interaction with bacteria. A Left, a hatchling Euprymna scolopes and its ventral light organ (black, dashed box). Right, schematic of the bilobed organ with three external pores per lobe. V. fischeri cells enter these pores and migrate down paths (red arrows) that lead to three independent crypts. Bottom, schematic of the formation of the interior symbiotic tissues over embryonic development on one half of the light organ; embryological day and standardized embryonic stage are based on [41]. B Confocal micrographs: Left, a high magnification of the three bacterial entry points or pores (P1-P3); Center, the bilobed light organ after full colonization by V. fischeri (magenta); Right, three crypts (C1-C3) of a single lobe showing mixed colonization (green and magenta) in the C1 and C2 crypts. C Confocal micrographs showing the crypts of one lobe of the light organ colonized for 24 h by the Cm-sensitive (Cm.^S) and GFP-labeled, wild-type strain (i.e., strain ES114 carrying pVSV102; see Table 1); then, for 24 h, either untreated (left) or treated with ≥50 μM Cm (right)