Figure 2(a) clearly shows that bacteroids of Rm11430 accumulate PHB during symbiosis, with numerous, electron-transparent, PHB granules visible within the
cytoplasm of the bacteroids when viewed by TEM. This is in contrast to bacteroids of Rm1021, shown in Figure 2(b), which demonstrate a notable absence of PHB. Figure 2 Bacteroids of Rm1021 (A) and Rm11430 (B). Electron-transparent PHB granules are clearly visible in bacteroids of Rm11430. PHB granules in the cytoplasm of the Rm11430 bacteroids are indicated in panel B. These granules are notably absent in the bacteroids of Rm1021 shown in panel A. Scale bar: 2 μm. Symbiotic assays with the host plant alfalfa revealed no significant difference between the phaZ mutant Rm11430 and the wild-type strain Rm1021. Plants inoculated with Rm11430 had an average shoot dry mass (SDM) of 10.56 mg compared to 10.80 mg for plants inoculated with Rm1021, both of which were CB-839 significantly different to the uninoculated controls, which had an average SDM of 4.16 mg. This is interesting since it suggests that PHB accumulation, as confirmed in Figure 2, does
not occur at the expense of symbiotic effectiveness. Competitiveness for nodule occupancy of Rm11430 The ability of S. meliloti Rm11430 to compete for nodule occupancy was assayed by co-inoculating alfalfa plants with different strain combinations. Table 4 shows that, when co-inoculated in approximately equal ratios with the wild-type strain, Rm11430 demonstrated no discernible this website difference in competitiveness relative to Rm1021. The percentage of Rm11430 in the original inoculum was similar to the percentage of nodules that it occupied. In agreement with previous studies [28], both Rm11105 (phaC) and Rm11107 very (bdhA) demonstrated significantly reduced competitiveness relative to wild-type. Table 4 also shows that both Rm11105 and Rm11107 demonstrate reduced competitiveness relative to Rm11430, with the phaC phenotype being more pronounced
than the bdhA phenotype. Table 4 Nodulation competitiveness of the S. meliloti wild-type strain and bdhA, phaC and phaZ mutants co-inoculated in the described ratios on M. GSK2118436 order sativa plants Strain (%) in inoculum No. nodules tested Nodule occupancy (%) Strain 1 Strain 2 Both Rm11430 (60) + Rm1021 (40) 18.0 61.1 22.2 16.7 Rm11430 (91) + Rm1021 (9) 15.0 93.3 6.7 0 Rm11430 (54) + Rm11105 (46) 16.0 100 0 0 Rm11105 (59) + Rm1021 (41) 15.0 6.70 93.3 0 Rm11105 (88) + Rm1021 (12) 20.0 5.00 75.0 20.0 Rm11430 (51) + Rm11107 (49) 20.0 65.0 35.0 0 Rm11107 (49) + Rm1021 (51) 14.0 21.4 78.6 0 Rm11107 (77) + Rm1021 (23) 15.0 86.7 0 13.3 Rm11107 (44) + Rm11144 (56) 19.0 94.7 0 5.30 The role of EPS in the establishment of nitrogen-fixing symbioses between S. meliloti and M. sativa has long been acknowledged [29], but the precise mechanism of interaction remains elusive.