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. 2010 Aug 20;192(20):5526–5533. doi: 10.1128/JB.00776-10

FIG. 6.

FIG. 6.

Expression of nifHDK and nitrogenase activity in strains CSRL16 and CSRL17. (A) RNA was isolated from cultures of the indicated strains grown with ammonium (0) and incubated in the absence of combined nitrogen for the times indicated in hours. Northern analysis was carried out with a probe of nifH, which was generated by PCR (see Materials and Methods). Sizes of previously identified nifH and nifHDK transcripts are indicated on the left. Hybridization with an rnpB gene probe was used as a loading and transfer control. (B) Ammonium-grown filaments were incubated in the absence of combined nitrogen in bubbled cultures for 24 h and then used for the determination of nitrogenase activity under oxic and anoxic conditions as described in Materials and Methods. Data are the means and standard deviations from 3 to 6 independent determinations.