[Utilization of D-histidine by the derivative strain TA100 of Salmonella typhimurium LT 2]

In general, wild-type gram-negative enteric bacteria are not able to utilize D-amino acids as the precursors of respective L-amino acids. We found, however, that an L-histidine auxotroph mutant, TA100, derived from Salmonella typhimurium strain LT 2 and used in the Ames test, showed a biphasic growth curve in the presence of both L- and D-histidine at concentrations of 5 micrograms/ml and 100 micrograms/ml, respectively. L-histidine may be utilized preferentially and then, after a short lag, D-histidine may be utilized. The short lag time is therefore considered to be the time required for induction of such an enzyme that converts D-histidine to L-histidine and for uptake of D-histidine by the bacterial cells.