Abstract

Six bacterial cultures isolated from soil were capable of growing in the presence of methotrexate (MTX). Two strains, PFR-1 and 3, developed resistance to 500 mug cm-3 MTX in the medium and produced elevated levels of the enzyme dihydrofolate reductase (EC 1. 5.1. 3): 2580 and 2702 U dm-3 compared to the sensitive parent strains (28 and 35 U dm-3). Isolate PFR-3 showed maximum enzyme production (4950 U dm-3, specific activity 12.56 U mg-1 in flasks and 5737 U dm-3, specific activity 14.80 U mg-1 in 5-dm3 fermenter) during exponential phase of growth (6 h) at 37-degrees-C and pH 7.0.