Characterization of the mutant strains NGRΩ<i>nopM</i> and NGR<i>nopM</i>(C338A).

<p>(<b>A</b>) Schematic representation of the knock-out mutant NGRΩ<i>nopM</i> (with an insertion of a 2-kb spectinomycin Ω interposon (Ωsp) at the constructed <i>Bam</i>HI restriction site) and of the point mutant NGR<i>nopM</i>(C338A) (cysteine 338 mutated to alanine; additional <i>Aor</i>51HI restriction site). (<b>B</b>) Immunoblot analysis of NopM of <i>Rhizobium</i> sp. NGR234 and indicated mutant derivatives. Immunoblots were performed with secreted proteins and the anti-NopM antibodies. As a loading control, secreted proteins in the molecular weight range of NopM were visualized on a parallel SDS-PAGE gel by silver staining (<b>C</b>) Symbiotic phenotype of <i>Rhizobium</i> sp. NGR234 (column 1), NGRΩ<i>nopM</i> (column 2), NGR<i>nopM</i>(C338A), (column 3), NGRΩ<i>nopM</i> carrying pFAJ-<i>nopM</i> (column 4) and NGR<i>nopM</i>(C338A) carrying pFAJ-<i>nopM</i> (column 5) on the host plant <i>L. purpureus</i> (cv. Chaojibiandou). In total, 70 plants (14 plants per strain) were inoculated. The numbers of nodules formed per plant were determined 35 days post inoculation. Data indicate means ± SE. Asterisks indicate significant reduced nodule formation as compared to the parent strain NGR234 (Kruskal-Wallis rank sum test; P<0.01).