TABLE 3.

Growth phenotypes of the different INH^r T^s mutants

Allele	Mutant classa	INH susceptibility (MIC, μg/ml)b	Thermosensitivityc	% Viability after 42°C incubationc	Nutrient supplement requiredd	ETH susceptibility (diam of inhibition zone ± SD)e	Relative Ndh activityf
ndh+		5	Tr	100	None	4.3 ± 0.3	1
ndh-4	I	>100	Ts lethal	4	CAA	0	0.04
ndh-14	I (0.4)	>100	Ts lethal	8	CAA	0.1 ± 0.3	0.04
ndh-15	II (0.4)	>100	Ts	40	Ser or Gly	0.4	0.18
ndh-21	III (0.2)	>100	Ts	40	None	2.7 ± 0.3	0.39

^aMutants were isolated from the laboratory wild-type strain mc²155 by INH^r selection 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 INH^r T^s 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. 

^bINH 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). 

^cThermosensitivity (T^s) was scored as the inability to grow at 42°C. The T^s 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. 

^dMany 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. 

^eETH 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. 

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