Table 5.
Sensitivity of wild‐type Xanthomonas citri ssp. citri strain 306 and derivative strains to different stresses and the antimicrobial peptide polymyxin B.*
| Strain | Survival rate (%)† | |||||||
|---|---|---|---|---|---|---|---|---|
| UV radiation | Heat shock | Saline stress | Osmolarity stress | Desiccation tolerance | SDS exposure | H2O2 exposure | Polymyxin B | |
| 306 | 18.9 ± 2.2 a | 14.6 ± 1.7 a | 3.4 ± 1.4 a | 6.2 ± 2.5 a | 1.6 ± 0.7 a | 0.1 ± 0.1 a | 33.3 ± 5.5 a | 56.8 ± 6.4 a |
| 247C8 (wxacO) | 4.2 ± 0.6 b | 5.1 ± 2.1 b | 0.3 ± 0.1 b | 0.9 ± 0.4 b | 0.2 ± 0.1 b | 0.0 ± 0.0 b | 10.5 ± 4.3 b | 10.9 ± 3.4 b |
| 236E9 (rfbC) | 3.4 ± 1.4 b | 6.6 ± 1.6 b | 0.3 ± 0.2 b | 1.2 ± 0.5 b | 0.2 ± 0.1 b | 0.0 ± 0.0 b | 14.3 ± 2.6 b | 8.5 ± 3.2 b |
| 247C8V | 5.5 ± 1.8 b | 4.2 ± 2.2 b | 0.3 ± 0.1 b | 0.7 ± 0.2 b | 0.3 ± 0.1 b | 0.0 ± 0.0 b | 13.8 ± 3.5 b | 14.2 ± 4.5 b |
| 236E9V | 4.8 ± 1.6 b | 5.3 ± 1.4 b | 0.3 ± 0.1 b | 0.9 ± 0.3 b | 0.4 ± 0.2 b | 0.0 ± 0.0 b | 12.2 ± 2.9 b | 11.2 ± 2.6 b |
| C247C8 | 16.6 ± 1.9 a | 13.2 ± 3.2 a | 2.9 ± 1.3 a | 5.7 ± 2.1 a | 2.1 ± 0.4 a | 0.1 ± 0.1 a | 36.4 ± 4.7 a | 49.7 ± 5.3 a |
| C236E9 | 16.2 ± 2.0 a | 15.3 ± 2.5 a | 3.6 ± 0.8 a | 7.0 ± 2.4 a | 1.4 ± 0.5 a | 0.2 ± 0.1 a | 31.2 ± 2.7 a | 51.4 ± 7.0 a |
Bacterial cell viability was estimated by plating on nutrient agar (NA) at 28 °C before (T0) and after (T1) treatment. Percentage survival was calculated as the ratio of viable cell counts at T1 to those at T0. The treatments were applied as follows: for UV radiation, an overnight bacterial culture was exposed to short‐wave UV irradiation (254 nm) for 15 min; for heat‐shock, the bacterial culture was incubated at 54 °C for 5 min; for saline stress, the bacterial culture was treated with 5% NaCl for 10 min; for osmotic stress, the bacterial culture was treated with 40% d‐sorbitol for 40 min; for desiccation stress, the bacterial culture was placed on glass coverslips and air dried in a laminar flow apparatus for 60 min, and then resuspended in 0.85% NaCl and plated; for sodium dodecylsulphate (SDS) exposure, the bacterial culture was treated with 0.1% SDS for 10 min; for sensitivity to hydrogen peroxide, the bacterial culture was exposure to 0.03% H2O2 for 10 min; for sensitivity to polymyxin B, the bacterial culture was treated with 0.5 µg/mL polymyxin B for 2 h. Bacterial cells were serially diluted with nutrient broth (NB) medium and the colony‐forming units (cfu) were counted after being cultured on NA plates for 48 h. Each test, plated in triplicate, was repeated three times with similar results.
Means and standard errors of three replicates from one representative experiment are shown. Data with the same letters in the same column are not significantly different at P < 0.05 (Student's t‐test).