Mobile DNA in the pathogenic .

The genus contains two pathogenic species of notable public health concern: and . These pathogens display a notable ability to undergo frequent programmed recombination events. The recombination mediated pathways of transformation and pilin antigenic variation in the are well studied systems that are critical for pathogenesis. Here we will detail the conserved and unique aspects of transformation and antigenic variation in the Transformation will be followed from initial DNA binding through recombination into the genome with consideration to the factors necessary at each step. Additional focus is paid to the unique type IV secretion system that mediates donation of transforming DNA in the pathogenic . The pilin antigenic variation system uses programed recombinations to alter a major surface determinant which allows immune avoidance and promotes infection. We discuss the - and - acting factors which facilitate pilin antigenic variation and present the current understanding of the mechanisms involved in the process.