TABLE 3.
Darkness response in R. rubrum wild-type and glnD mutant strains
| Strain | Chromosomal genotype and gene on plasmid | Nitrogenase activity (units) before and after dark-light shiftsa
|
||
|---|---|---|---|---|
| Initial | 60 min dark | 10 min light | ||
| UR2 | Wild type | 800 | 90 (11%) | 720 (90%) |
| UR1120 | glnD1::aacC1 mutant with Kp nifA (pCK3) | 800 | 140 (18%) | 720 (90%) |
| UR1330 | ΔglnD3::aacC1 mutant with Kp nifA (pCK3) | 620c | 120 (20%) | 170 (28%) |
| UR1331 | ΔglnD4::aacC1 mutant with Kp nifA (pCK3) | 650c | 120 (18%) | 160 (25%) |
| UR1332 | ΔglnD3::aacC1 with 5′ region of glnD (pUX1224) | 700 | 175 (25%) | 770 (110%) |
| UR1333 | ΔglnD4::aacC1 with 5′ region of glnD (pUX1224) | 670 | 160 (24%) | 710 (106%) |
| UR1387 | ΔglnD4::aacC1 with integration of 5′ region of glnD | 360 | 65 (18%) | 365 (101%) |
| UR1388 | ΔglnD4::aacC1 with integration of glnD+ | 700 | 65 (9%) | 665 (95%) |
| UR1389 | ΔglnD3::aacC1 with integration of 5′ region of glnD | 350 | 65 (19%) | 370 (106%) |
| UR1390 | ΔglnD3::aacC1 with integration of glnD+ | 720 | 60 (8%) | 770 (107%) |
| UR1401 | ΔglnD3::aacC1 draG4 with Kp nifA (pCK3) | 140 | 30 (21%) | 55 (39%) |
| UR1402 | ΔglnD4::aacC1 draG4 with Kp nifA (pCK3) | 150 | 35 (23%) | 55 (37%) |
Nitrogenase activity was derepressed in MG medium under illumination and assayed before the shift to the dark (initial), 60 min after cells were shifted to the dark, and 10 min after cells were returned to light. Each unit of nitrogenase activity is expressed as nanomoles of ethylene produced per hour per milliliter of cells at an optical density at 600 nm of 1. Each activity value is from at least 10 replicate assays from different individually grown cultures. The standard deviation is about 10 to 15%. The values in parentheses are the percentages of the initial nitrogenase activity remaining after the shift to darkness or reillumination. UR1330 and UR1331 grew significantly more slowly than did other strains in MG, so that they had lower total nitrogenase activity, even though the initial specific activity was very similar to that of wild-type and other strains.