Markerless deletions of pil genes in Myxococcus xanthus generated by counterselection with the Bacillus subtilis sacB gene

In-frame deletions of pilA and pilS were constructed in Myxococcus xanthus with a plasmid integration-excision strategy facilitated by sacB. sacB conferred sucrose sensitivity upon its M. xanthus host only when it lay in the same orientation as adjacent M. xanthus genes. Gene orientation also affected the efficiency of sucrose counterselection in the sucrose-sensitive strains. The Delta pilA mutant lacked pill and social motility, while the Delta pilS mutant showed no defect in either phenotype.