Table 2.

Growth characteristics of and nirI promoter activities in mixed cultures of NirS- and NorC-deficient mutant cells

Starting ratio (NorC:NirS)aCharacteristic at the end of growthb
GasNitriteOD660Final ratio (NorC:NirS)Activity of nirIin NirS cells (Miller units)
1:0+0.191:0NAc
4:1+1.921:1.8541
2:1+2.391:6.8487
1:1++2.311:7.4460
1:2+++1.891:12.5306
1:4+++0.951:17220
0:1++0.400:135
  • a The cells were grown separately under aerobic conditions and then mixed together at the various starting ratios listed till a final optical density at 660 nm (OD600) of 0.1 was reached and further incubated under denitrifying conditions.

  • b Gas (as reflected by air bubbles on top of the cultures) was not produced (−) or was produced (+). Nitrite concentration in the culturing medium was determined with Nitur strips as not detectable (−), less than 5 mg/liter (+), or more than 5 mg/liter (++). Final ratios of NorC- and NirS-deficient mutant cells were calculated on the basis of the number of colonies obtained after plating appropriate dilutions of the cultures on plates with kanamycin (both strains can grow) and with kanamycin and streptomycin (only the NirS-deficient mutant can grow).

  • c NA, not applicable.