FIG. 1.
Agarose gels of PCR products to identify guaB genotype of individual B. burgdorferi colonies. (A) Initial screen of coumermycin-resistant colonies, showing identification of B31-80, with bands indicating the presence of both wild-type (white arrowhead) and mutant (guaB::gyrBr; black arrowhead) copies of the guaB gene. The PCR product corresponding to the mutant locus is consistently weaker than that derived from the wild-type locus, most likely because the larger fragment is poorly amplified in the conditions used. (B) Rescreen of individual colonies derived from B31-80. Most (e.g., 74) remain heterozygous, whereas 87 represents a homozygous mutant colony. Amplification controls: lanes 1, reagent blank; 2, wild-type DNA; 3, guaB::gyrBr DNA; 4, blank spot on transformation plate.