FIG. 1.

ID₅₀ of V. fischeri for symbiotic colonization. In two separate experiments juvenile squid were incubated with different numbers of V. fischeri ES114 cells, and the percentage of animals subsequently colonized was determined. The dose at which 50% of the animals became luminescent by 48 h postinoculation, indicated by the dotted lines and black arrow, was determined using the equation y = 0.3735 lnx − 1.794 for experiment 1 (circles) and the equation y = 0.1381 lnx − 0.2459 for experiment 2 (triangles).