TABLE 4

Characteristics of parental strains and the three classes of methylammonium-resistant mutants

Methylammonium (mm)
StrainaSelected atResistant atbUptake of [14C]methylammonium (pmol/μg
 chlorophyll a + b/min)c
Wild type
 4A+<0.0580
 CC-125<0.0535
Class 1
 CR05d11e <2
 CR430.051e <2
Class 2
 CR0251 3.5
 CR030.10.1 6.0
 CR040.11 2.0
 CR07d11 3.5
 CR390.051 3.0
 CR400.051 3.5
 CR420.051 4.0
 CR460.050.1 7.0
 CR470.051 3.0
 CR480.051 3.5
 CR490.051 3.5
 CR500.050.1 10
Class 3
 CR410.050.0530
 CR450.050.0540
  • a The parental strain for CR03 and CR04 was CC-125. For all others it was 4A+.

  • b Highest concentration of methylammonium to which the strain was resistant with arginine as N source. The concentrations tested were 0.05, 0.1, and 1 mm.

  • c Rates of uptake were determined from data in Figure 4 and similar experiments. Averages for three experiments are shown except for strains CC-125, CR03, and CR04, which were assayed only once. For parental strains, rates were determined from early time points when <20% of the substrate had been utilized and for mutant strains during the first 15 min.

  • d Subjected to selection twice (see materials and methods).

  • e Grew slowly at 1.0 mm methylammonium.