TABLE 1.

Comparative colonization characteristics of V. fischeri strains

V. fischeri strain	Host speciesa	Inoculum concn (CFU/ml) resulting in a 50% infection rateb	Total CFU per light organ (104) after 48 hc
ES114	E. scolopes	750	42
ES12	E. scolopes	400	25
ES213	E. scolopes	ND	46
ES401	E. scolopes	ND	90
EM17	E. morsei	200	42
EM18	E. morsei	100	31
EM24	E. morsei	70	17
MJ11	M. japonica	10,000	4.5
CG101	C. gloriamaris	2,000	0.62

^aStrains were isolated from light organ homogenates of the indicated host species (5). Each isolate was obtained from a different animal. 

^bFor each strain, groups of 10 newly hatched E. scolopes squids were exposed for 3 h to seawater containing between 10² and 10⁵ V. fischeri cells per ml. The approximate concentrations of cells that were required to infect 50% of the juvenile animals are given. ND, not determined. 

^cSymbiont cell numbers (CFU) were estimated by homogenizing the light organ and plating serial dilutions on a nutrient medium (69).