TABLE 3.

Free-living and symbiotic phenotypes of B. japonicum USDA110 mutants with increased N₂OR activity^a

Strain	N2OR activity (nmol h−1 109 cells−1)b	Generation time (h)c	Frequency of occurrence of Kmr colonies	Number of nodules (plant−1)	Nodule wt (mg [fresh wt] nodule−1)	Nitrogen-fixing activity (μmol C2H4 produced h−1 g of nodule [fresh wt]−1)d
USDA110	12 ± 1¶	10.0 ± 1.2*	1.9 × 10−7 ± 0.6 × 10−7*	52 ± 7*	13.0 ± 1.7*	12.2 ± 3.8*
5M08	107 ± 0#	9.6 ± 0.0*	1.3 × 10−7 ± 0.3 × 10−7*	102 ± 8#	5.8 ± 0.9#	0.0 ± 0.0#
5M09	85 ± 4§	9.7 ± 0.6*	1.1 × 10−7 ± 0.4 × 10−7*	52 ± 14*	11.3 ± 4.2*	14.4 ± 2.8*
5M14	114 ± 2#,§	10.1 ± 0.6*	2.0 × 10−7 ± 0.4 × 10−7*	48 ± 12*	10.4 ± 3.1*	26.8 ± 6.2*
20M19	138 ± 2*	11.7 ± 0.9*	3.3 × 10−7 ± 1.0 × 10−7*	49 ± 10*	13.5 ± 3.4*	0.8 ± 0.8#

^aValues are expressed as means ± standard deviations (n = 3). Values in the same column followed by the same symbols (*, #, §, and ¶) do not differ significantly by t test (P < 0.05).

^b5M08, 5M09, and 5M14 were obtained from 5% N₂O selection, while 20M19 was derived from 20% N₂O selection.

^cGeneration times were calculated from growth in HM broth medium.

^dNitrogen-fixing activity was evaluated by measuring ARA.