Table 4. Nitrogenase activity in R. rubrum strains containing single or multiple copies of R. rubrum nifA when grown in MG (nitrogen-limiting) or MN− (NH4+ -free) media.
| Strain | Plasmid (gene) | Nitrogenase activity* | |
|---|---|---|---|
|
| |||
| MG (nitrogen-limiting)† | MN− (NH4+-free)‡ | ||
| UR2 (wild-type) | None (single copy of R. rubrum nifA) | 800 | 400 |
| UR717 (ΔglnB3) | None (single copy of R. rubrum nifA) | <10 | <10 |
| UR741 (wild-type) | pYPZ239 (multicopy of R. rubrum nifA) | 650 | 300 |
| UR744 (ΔglnB3) | pYPZ239 (multicopy of R. rubrum nifA) | 50 | 280 |
*
Units of nitrogenase activity are expressed as in Table 2.
†
Nitrogenase activities of these strains in MG medium are similar to those recorded previously (Zhang et al., 2001a).
‡
UR717 grew very slowly in MN− medium, with a final OD600 of 0.3 after 2 days of growth, while UR2 and UR741 had a final OD600 of ∼3. UR744 grew slightly slower in MN− medium, with a final OD600 of 1.7.