Table 2.

β-Galactosidase activities of the translationalnifH-lacZY fusion recombined into the chromosomes of the wild-type and mutant strains of A. caulinodans carrying or not carrying the constitutively expressed nifAfrom A. caulinodans orB. japonicum

Strainβ-Galactosidase sp acta
N free, 3% O2bNH4+, 3% O2cNH4+, aird
57721 (wild type)14,229.0 ± 3,876.534.6 ± 32.510.5 ± 0.81
57820 (glnBmutant)20,123.0 ± 5,480.322.6 ± 18.314.6 ± 11.1
57821 (glnKmutant)9,804.6 ± 953.86.2 ± 5.54.0 ± 0.3
57720 (nifAmutant)11.5 ± 9.33.3 ± 2.39.9 ± 9.9
57825 (glnB glnKmutant)7,661.7 ± 478.86,535.4 ± 532.110.7 ± 8.3
57720 (nifA mutant)/ pRS1022e 17,169.6 ± 3,463.291.0 ± 27.35.5 ± 2.7
57820 (glnB mutant)/ pRS1022e 28,319.8 ± 4,652.6305.5 ± 221.89.7 ± 0.6
57821 (glnK mutant)/ pRS1022e 15,791.0 ± 3,111.6798.6 ± 205.113.4 ± 7.3
57720 (nifA mutant)/ pRJ7556e 31,650.4 ± 6,762.719,878.6 ± 6,333.1175.75 ± 71.5
  • a Specific activity of β-galactosidase in pure culture expressed in Miller units · mg of protein−1. Values are the means ± standard deviations from at least three independent experiments.

  • b Cells were cultured for 4 h in nitrogen-free medium under microaerobic conditions.

  • c Cells were cultured for 4 h in minimal medium containing 20 mM NH4 + under microaerobic conditions.

  • d Cells were cultured for 4 h in minimal medium containing 20 mM NH4 + in the presence of air.

  • e pRS1022 contains the constitutively expressednifA from A. caulinodans (15), and pRJ7556 contains that from B. japonicum(12).