title: High-frequency RecA-dependent and -independent mechanisms of Congo red binding mutations in Yersinia pestis.
abstract: Yersinia pestis, which causes bubonic and pneumonic plague, forms pigmented red colonies on Congo red (CR) dye agar. The hmsHFRS genes required for CR binding (Crb(+)) are genetically linked to virulence-associated genes encoding a siderophore uptake system. These genes are contained in a 102-kb chromosomal pgm locus that is lost in a high-frequency deletion event, resulting in loss of the Crb(+) phenotype. We constructed a recA mutant strain of Y. pestis KIM10+ (YPRA) to test whether the high frequency Crb mutants result from a RecA-mediated deletion of the IS100-flanked pgm locus. Two Pgm-associated phenotypes (Crb(+) and pesticin sensitivity [Pst(s)]) were used as markers for the presence of the pgm locus in the RecA(+) KIM10+ and RecA(-) YPRA strains. In KIM10+, both phenotypes were lost at a very high (2 x 10(-3)) frequency, due to the deletion of the entire pgm locus. In YPRA, the Crb(+) phenotype was still lost at a high frequency (4.5 x 10(-5)), although the loss of the Pst(s) phenotype occurred at spontaneous antibiotic resistance mutation frequencies (2 x 10(-7)). These RecA-independent Crb(-) mutants were caused by mutations in both the hmsHFRS locus and in a newly identified gene, hmsT. Nonpigmented Yersinia pseudotuberculosis and Escherichia coli strains transformed with both hmsT and hmsHFRS became Crb(+). This study demonstrates that in a laboratory culture, the Crb(+) phenotype is unstable, independent of the pgm locus deletion. We propose that a lack of selection for the CR-binding ability of Y. pestis in vitro may contribute to the mutation frequencies observed at the hmsHFRS and hmsT loci.
authors.affiliation: Department of Biomedical Sciences, University at Albany, State University of New York, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Hare
authors.forename: K A
authors.initials: KA
authors.lastname: McDonough
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins; D002874:Chromosome Mapping; D003224:Congo Red / Q000378:metabolism / Q000494:pharmacology*; D017931:DNA Primers; D017353:Gene Deletion; D005787:Gene Frequency; D006427:Hemin / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D016296:Mutagenesis; D010641:Phenotype; D010957:Plasmids; D011485:Protein Binding / Q000235:genetics; D011938:Rec A Recombinases / Q000235:genetics* / Q000378:metabolism*; D014170:Transformation, Genetic; D015010:Yersinia pestis / Q000235:genetics* / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D017931:DNA Primers; C082669:HmsF protein, Yersinia pestis; C082666:HmsH protein, Yersinia pestis; C082670:HmsR protein, Yersinia pestis; D008565:Membrane Proteins; D003224:Congo Red; D006427:Hemin; D011938:Rec A Recombinases