Growth abilities and phenotype stability of a sulcotrione-degrading Pseudomonas sp. isolated from soil

• Growth of sulcotrione-degrading Pseudomonas sp.1OP was optimal at initial neutral pH.
• An optimal sulcotrione concentration was determined for growth of the isolate.
• Degrading phenotype appears to be an unstable trait of the strain.
• Degrading capability of the isolate was due to the presence of a catabolic plasmid.

Pseudomonas sp. 1OP, previously isolated from a French agricultural soil, has been described as the first sulcotrione degrading bacteria. Different conditions of initial pH and herbicide concentration in liquid culture were tested to evaluate the growth performances of the isolate and its degrading capacity, with sulcotrione as the sole carbon and/or energy source. Maximal growth rate (μmax) was obtained under initial neutral conditions and with initial concentration of sulcotrione close to 180 μM, and was described, during the exponential phase, by a sigmoidal curve which could be easily fitted to the modified Gompertz equation. Complementary studies carried on the CMBA by-product and on another β-triketone herbicide showed the relative specificity of the strain against sulcotrione. The sulcotrione degrading phenotype of Pseudomonas sp.1OP was shown to be lost under non-selective conditions. Plasmid-Eckardt modified method, consecutively applied for plasmid profiling, showed that this strain carries one large plasmid (>12 kb) bearing putative genes involved in sulcotrione degradation, as demonstrated by curing experiment.