Table S1.
Strains and plasmids used
| Strain or plasmid | Genotype or phenotype | Source |
| R. palustris strains | ||
| CGA009 | WT strain; spontaneous CmR derivative of CGA001 | 19 |
| CGA676 | nifA*; 48-bp deletion encoding Q-linker amino acids 202–217; produces H2 in the presence of NH4+ | 7 |
| CGA676 nifDV75AH201Q | CGA676 in which the nifDV75AH201Q mutation was introduced at its native locus using allelic exchange | This study |
| CGA679 | ΔcbbLS::Kmr ΔcbbM mutant of CGA676 | 7 |
| CGA679 nifDV75AH201Q | CGA679 in which the nifDV75AH201Q mutation was introduced at its native locus using allelic exchange | This study |
| CGA676 his::nifD | CGA676 in which the his::nifD was introduced at its native locus using allelic exchange | This study |
| CGA676 his::nifDV75AH201Q | CGA676 in which the his::nifDV75AH201Q was introduced at its native locus using allelic exchange | This study |
| E. coli strains | ||
| DH5α | F−λ− recA1 Δ(lacZYA-argF)U169 hsdR17 thi-1 gyrA96 supE44 endA1 relA1 Φ80lacZΔM15 | Gibco-BRL |
| S17-1 | thi pro hdsR hdsM+ recA; chromosomal insertion of RP4-2 (Tc::Mu Km::Tn7) | 23 |
| Plasmids | ||
| pJQ200SK | GmR, sacB; mobilizable suicide vector | 24 |
| pJQ-nifD | GmR; nifD coding sequence cloned into the PstI site of pJQ200SK | This study |
| pJQ-nifDV75AH201Q | GmR; nifDV75AH201Q coding sequence cloned into the PstI site of pJQ200SK | This study |
| pJQ-his::nifD | GmR; nifD coding sequence with an his8x tag encoded at the N terminus cloned into the PstI site of pJQ200SK | This study |
| pJQ- his::nifDV75AH201Q | GmR; nifDV75AH201Q coding sequence with an his8x tag encoded at the N terminus cloned into the PstI site of pJQ200SK | This study |