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Role of tfxE, but Not tfxG, in Trifolitoxin Resistance

Alexandra J. Scupham,^1, Yuemei Dong,² and Eric W. Triplett^2*

Departments of Bacteriology,¹ Agronomy, University of Wisconsin—Madison, Madison, Wisconsin 53706²

Received 4 March 2002/ Accepted 17 June 2002

Eight genes, tfxABCDEFG and tfuA, confer production of trifolitoxin (TFX), a ribosomally synthesized, posttranslationally modified peptide antibiotic, in TFX-sensitive -proteobacteria. An in-frame deletion in tfxE significantly reduced a strain's resistance to TFX in comparison to that of an otherwise identical construct containing wild-type tfxE. The deletion of tfxG had no effect on TFX resistance. Nevertheless, RNase protection assays showed that tfxE and tfxG are transcribed, showing that the tfxDEFG mRNA was produced on the same transcript. Examination of the role of tfxG in TFX production showed that the tfxG mutant expressed slightly less TFX activity and produced only one TFX isomer while four are produced by the wild-type strain. Thus, tfxE plays an important role in TFX resistance while tfxG is important in optimal TFX production through the production of TFX isomers.

Present address: Department of Plant Pathology, University of California, Riverside, CA 92521.