Effects of rho-fluorophenylalanine on the growth of Lactobacillus arabinosus

p-Fluorophenylalanine has been found to be inhibitory to Lactobacillus arabinosus 17-5. This inhibition has been shown to be competitive with phenylalanine but not with tyrosine, and is described by a low antibacterial index, which varies over a range of approximately 1–20, dependent upon the temporal stage of the culture for which the data are employed in calculation.The organism has been found also to adapt readily to the inhibitor. Evidence that this adjustment involves a mutation to a type with a selective advantage in media containing the inhibitor is presented.Under limiting conditions, which have been described, the organism is capable of greater growth in the presence of both metabolite and antimetabolite than in the presence of the same amount of metabolite alone.Discussion of the significance of the results has been presented.