A clone bank, consisting of approx. 8100 colonies, has been created for the spirochete Leptospira biflexa serovar patoc in Escherichia coli using pBR322 as the vector. One of these clones contains the genetic information needed to complement a defect in the trpE gene of E. coli. The information resides on a 20.5-kb plasmid designated pYC1, which carries a 16-kb insert consisting of three HindIII fragments. It does not complement defects in other genes needed for the biosynthesis of tryptophan in E. coli.