TABLE 2.
Phenotypic characterization of P. fluorescens CHA0 spontaneous regulatory mutantsa
| Characteristic | Wild type | gacA mutant | gacS mutant |
|---|---|---|---|
| Colony morphology on KB agar and NBY agar | Circular, smooth, convex, opaque, beige | Generally flat, translucent, orange, 10 to 50% greater diam | Generally flat, translucent, orange, 10 to 50% greater diam |
| Cell length (μm) | 3.3 (0.5) | 5.8 (1.1) | 5.3 (0.8) |
| Pyochelin concn (ng/108 CFU) | 19.2 (4.6) | 125.5 (19.1) | 143.9 (11.3) |
| Salicylic acid concn (ng/108 CFU) | 0.6 (0.3) | 4.2 (1.1) | 7.1 (2.9) |
| Extracellular protease | +b | − | − |
| TSO | + | − | − |
| Hydrogen cyanide | + | − | − |
| PHL concn (ng/108 CFU) | 61.8 (2.5) | <0.07 | <0.07 |
| Pyrrolnitrin concn (ng/108 CFU) | 2.5 (0.9) | <0.1 | <0.1 |
| PLT concn (ng/108 CFU) | 12.5 (1.5) | <0.07 | <0.07 |
| Nutrient broth pH after 48 h | 7.77 (0.02) | 8.04 (0.03) | 8.09 (0.04) |
| Inhibition zone for P. ultimum growth (mm) on: | |||
| KB agar | 1.03 (0.12) | 0.97 (0.09) | 0.93 (0.03) |
| KB agar containing 100 μM FeCl3 | 1.43 (0.09) | 0.03 (0.03) | 0.07 (0.07) |
| % Cucumber seedlings standing after 7 days in P. ultimum-infested soil | 82.5 (3.8) | 35.7 (5.4) | 31.1 (4.2) |
a
The values are data for wild-type strain CHA0 and 5 to 10 mutants complemented with gacS and gacA clones. The values in parentheses are standard errors. Each treatment was replicated two to five times.
b
+, strong positive reaction; −, strong negative reaction, although some leakiness was observed in mutants.