FIG. 6.

Confocal micrograph of fluorescently labeled V. fischeri cells colonizing the light organ of a juvenile E. scolopes squid. A 1:1 ratio of red and green fluorescent protein-expressing cells of V. fischeri strain MB13B2 was incubated with freshly hatched juvenile E. scolopes for 12 h at a total concentration of 4,500 CFU/ml. After an additional 36 h of symbiotic development, light organs were fixed and the animal tissue was stained (blue) and observed for the presence of mixed or single-color bacterial populations in each morphologically distinguishable crypt. The entire light organ (light blue outline) contains six crypts outlined with colored ovals. Two (33%) of the six crypts were cocolonized (yellow with a red and green dashed outline), while four (67%) were colonized by a single strain (either red or green and outlined with the corresponding solid color). Bar = 100 μm.