Genomic DNA encoding the pseudomonas fluorescens alternative sigma factor, RpoS, capable of activating gene expression

DETAILED DESCRIPTION OF THE INVENTION Pseudomonas fluorescens strain 915 was isolated from the roots of a cotton plant grown in a Texas cotton field and was identified as an effective biocontrol strain of Pythium ultimum- and Rhizoctonia solani-induced damping off of cotton.
We have determined that certain mutant derivatives of the bacterial biological control strain Pseudomonas fluorescens strain 915 are deficient or altered in a variety of functions.
Such pleiotropic mutants can be isolated following mutagenesis techniques known to those skilled in the art (e.
g.
nitrosoguanidine mutagenesis, transposon mutagenesis) or can arise spontaneously.
One such mutant, obtain after mutagenesis with the chemical mutagen nitrosoguanidine was designated mutant 2-1.
Seven further mutants were identified by introducing the transposon TnCIB116 into strain 915.
These mutants can be identified on the basis of their inability to inhibit in vitro the growth of the phytopathogenic fungus Rhizoctonia solani.
They also fail to synthesize the antifungal metabolite pyrrolnitrin, and no longer produce cyanide or the enzyme chitinase, each of which has the potential to inhibit fungal growth (Voisard et al.
, EMBO J.
8:351-358 (1989); Jones et al.
, EMBO J.
5:467-473 (1986)).
The mutants' production of an enzyme with gelatinase activity is significantly reduced, and they have an altered colony morphology.
A summary comparing the characteristics of the pleiotropic mutants with the corresponding characteristics of wild-type P.
fluorescens strain 915 is presented in Table 1.

TABLE 1
______________________________________
Characteristic
P.
fluorescens strain 915
Pleiotropic mutants
______________________________________
Pyrrolnitrin + -
Cyanide + -
Chitinase + -
Gelatinase + reduced
Colony morphology
circular, entire,
circular, undulate,
convex and opaque
flat and translucent
Inhibition of Rhizoctonia
+ -
solani
______________________________________
A total of eight pleiotropic mutants was identified