Abstract
Deoxythiamine (DOB_1) having hydrogen in the place of hydroxy group of thiamine (B_1) is a B_1 antagonist. Its inhibition indices on growth and B_1-uptake of Lactobacillus fermenti are about 250 and 6,respectively.^<7)8)> After the everyday subculture of the organism in serial media in increasing concentration of DOB_1,L. fermenti has been mutated. The resistant cells were appeared in the medium containing 1μg of B_1 and more than 800μg of DOB_1 and they were hardly reversible. The resistant cells showed similar B_1 response curve to the original cells and the same level of both B_1-uptake and inhibition of the B_1-uptake by DOB_1 as the original. The most distinguished character of the resistant cells is that they exhibit good growth in the medium containing a high dose of DOB_1 (more than 500μg per 4ml broth) and no B_1. It has been postulated that there is a new metabolic pathway of DOB_1 which may be converted to TDP and no change at the site of B_1-uptake system.
