CLONING OF THE FLII GENE FROM RHODOBACTER-SPHAEROIDES WS8 BY ANALYSISOF A TRANSPOSON MUTANT WITH IMPAIRED MOTILITY

A transposon mutant of Rhodobacter sphaeroides WS8 was isolated that s howed reduced swarming on soft agar plates. Liquid cultures of this mu tant (M18) showed a low percentage of motile swimming cells in mid-exp onential phase and a low level of extracellular flagellin protein by W estern blotting. M18 was complemented by a clone from a library of R. sphaeroides WS8 DNA, and restriction mapping of the site of TnphoA ins ertion in the mutant, coupled with DNA sequencing, showed that it had a defect in the fliI gene. To determine if a partly functional fliI ge ne was giving the low-motility phenotype of M18, a drug resistance ome ga cartridge was inserted into the gene to give a complete null mutant . This null strain also produced a low percentage of motile cells. Pos sible reasons for this apparent fliI-independent flagellar formation a re discussed.