Diversity, Evolution, and Environmental Distribution of Reductive Dehalogenase Genes

Abstract

Reductive dehalogenases, the active enzymes in organohalide respiration, are a diverse protein family with low sequence similarity and a punctuated distribution across the tree of life. The diversity, environmental distribution, and evolution of the reductive dehalogenases remain open questions. This chapter describes reductive dehalogenase sequence similarity and domain architecture, highlighting why predicting substrate specificity from sequence similarity is unreliable for these enzymes. Common in contaminated environments, but also identified in soda lakes, ocean sediment, and even as part of the human microbiome, the global distribution of reductive dehalogenases is broad and continually expanding. A map view of current locations where reductive dehalogenases have been detected provides compelling evidence for the ubiquity of these proteins in the environment, in keeping with predictions of an ancient origin for the group. The evolutionary history of the reductive dehalogenases includes vertical inheritance alongside a myriad of mechanisms for lateral transfer, including integrases, circularizing transposable elements, and, possibly, phage-mediated transfer. The reductive dehalogenases remain incompletely characterized from the perspectives of sequence diversity, substrate specificities, global distribution, and modes of inheritance.