Pleiotropic Effects of Regulatory ros Mutants of Agrobacterium radiobacter and Their Interaction with Fe and Glucose. G. Brightwell. School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, U.K. H. Hussain, A.Tiburtius, K. H.Yeoman and A.W.B. Johnston. School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, U.K. MPMI 8:747-754. Accepted 27 April 1995. Copyright 1995 The American Phytopathological Society.

Four exo mutants of Agrobacterium radiobacter, defective in the synthesis of acidic exopolysaccharide were complemented by a gene from that species, which is similar to the transcriptional regulator, ros, of A. tumefaciens. It was confirmed that this A. radiobacter gene, which we term rosAR, like ros, repressed its own transcription as well as that of virC and virD, two loci involved in lumorigenesis. The sequence of RosAR suggested that it might bind to a transition metal and its repressor abilities were shown to require Fe in the medium; repression was also enhanced with increasing levels of glucose. Certain rosAR mutants, in which its 3' end was removed were dominant; i.e., when plasmids containing such mutant forms of the gene were introduced into wild-type A. radiobacter, the transconjugants were nonmucoid. Such effects were also seen in a wide range of bacteria, including Escherichia coli and Xanthomonas. Several mutants that were complemented by rosAR also accumulated protoporphyrin, suggesting a defect in haem synthesis.