Table 3.

Growth phenotypes of the different INHrTs mutants

AlleleMutant classaINH susceptibility (MIC, μg/ml)bThermosensitivityc% Viability after 42°C incubationcNutrient supplement requireddETH susceptibility (diam of inhibition zone ± SD)eRelative Ndh activityf
ndh + 5Tr 100None4.3 ± 0.31
ndh-4 I>100Tslethal4CAA0  0.04
ndh-14 I (0.4)>100Tslethal8CAA0.1 ± 0.30.04
ndh-15 II (0.4)>100Ts 40Ser or Gly0.40.18
ndh-21 III (0.2)>100Ts 40None2.7 ± 0.30.39
  • a Mutants were isolated from the laboratory wild-type strain mc2155 by INHrselection at 30°C. The mutants were grouped according to their ability to grow on minimal medium. The number in parentheses is the fraction of spontaneous INHr Ts mutants that are of this class. Data for two class I mutants are presented to show that the phenotypes of the ndh-4 mutant are not an artifact of mutagenesis.

  • b INH susceptibility was determined as the minimum concentration that reduced the number of CFU 100-fold (see Materials and Methods). Susceptibility was tested at the permissive temperature (30°C).

  • c Thermosensitivity (Ts) was scored as the inability to grow at 42°C. The Ts lethal mutants could not survive 42°C incubation for 2.5 days, as indicated by a >90% reduction in viability after 42°C incubation. This viability, measured as the number of CFU that formed after transfer to the permissive temperature divided by the CFU of that culture, is the average of values from three different experiments.

  • d Many of the mutants failed to grow on minimal medium plus glycerol or glucose at the permissive temperature. Some mutants required supplementation of Casamino Acids (CAA); others grew on minimal medium supplemented with serine or glycine.

  • e ETH susceptibility was determined as the diameter of the zone (in millimeters) in which growth was inhibited by the drug; 500 μg was applied in a 10-μl volume.

  • f Ndh activity is the rate of NADH oxidation with menadione as an electron acceptor (see the Fig. 3 legend and Materials and Methods).