The Gram-negative anaerobe is the causative agent of footrot in sheep. The authors have previously characterized two genetic elements, the () and elements, which integrate into the genome of . In the virulent strain A198 there are two copies of the element. One copy is integrated into the 3’ end of the gene, close to the aspartokinase () gene, and the second copy is integrated into the 3’ end of the gene, next to the polynucleotide phosphorylase () gene. In this study, a new genetic element was identified in the benign strain C305, the element, integrated into the 3’ end of the gene, next to . The element was found in most strains, both benign and virulent, which were examined, and was integrated into in most strains. Between the and genes, a gene (designated ), was identified whose predicted protein product has very high amino acid identity with RsmA from the plant pathogen . RsmA acts as a global repressor of pathogenicity in , by repressing the production of extracellular enzymes. In virulent strains of the element was found to be integrated next to , and either the or element was integrated next to . By contrast, all but one of the benign strains had at one or both of these two positions, and the one exception had neither nor at one position. The loss of the element from the virulent strain 1311 resulted in loss of thermostable protease activity, a virulence factor in . A model for virulence is proposed whereby integration of the and genetic elements modulates virulence by altering the expression of and .


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