FIG. 1.

Strategy for mutagenesis of sspB. The gray and checkered boxes within sspA and sspB, respectively, represent the regions of divergent sequence of these genes. The remainder of the genes share 90% identity (5). The divergent region from sspB was PCR amplified and cloned into pUC18. The kanamycin resistance gene (aphAIII) was PCR amplified and cloned into the HindIII site in the sspB fragment. The sspB::aphAIII fragment was excised from the vector, gel purified, and transformed into strain DL1 to construct the sspB mutant PK3246 and into strain OB220 (12) to generate the sspAB double mutant PK3247.