Role of leuX in Escherichia coli colonization of the streptomycin-treated mouse large intestine.

Escherichia coli F-18, a normal human fecal isolate, is an excellent colonizer of the streptomycin-treated mouse large intestine. E. coli F-18 Col-, a derivative of E. coli F-18 that no longer makes the E. coli F-18 colicin, colonizes the mouse large intestine as well as E. coli F-18 when fed alone, but is eliminated when fed together with E. coli F-18. Recently, a random bank of E. coli F-18 DNA was transformed into E. coli F-18 Col-, the resultant population was fed to streptomycin-treated mice, and the intestine was used to select the best colonizer. In this fashion, a 6.5 kb E. coli F-18 DNA fragment was isolated. This fragment was shown to enhance E. coli F-18 Col- mouse large intestinal colonizing ability and survival during stationary phase in intestinal mucus in vitro, as well as stimulate the synthesis of type-1 fimbriae. Here, we present evidence that the gene responsible for the enhanced E. coli F-18 Col- colonizing ability and survival during stationary phase in vitro is leuX. This gene encodes a rare leucine tRNA specific for the UUG codon. In addition, we show that the presence of a functional leuX gene is necessary for E. coli K-12 intestinal colonization and for survival in stationary phase.