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Battles in the outer space: Extracellular DNases secreted by Pectobacterium carotovorum and its host plants

Zhongguo Xiong: University of Arizona

<div>Extracellular DNA (exDNA) plays a plethora of roles in the microbe and host interactions. exDNA is an important component of bacterial biofilms, aiding bacterial colonization and survival while exDNA secreted by human, animal, and plant hosts plays significant roles in defense against microbial infections. To investigate the roles of extracellular DNases (exDNases) in this warfare, we characterized the exDNases secreted by <em>Pectobacterium carotovorum</em> and pea (<em>Pisum sativum</em>) root tips. In DNase agar plate assays, exDNase activities were detected from both <em>P. carotovorum</em> and pea root tips, but the activities increased significantly when the two were co-cultured together. Biochemical characterizations indicated the presence of DNase II-like endonuclease and exonuclease activities secreted from pea root tips and DNase I-like endonuclease and exonuclease activities secreted from <em>P. carotovorum</em>. In-gel PAGE DNase assays determined a single protein of ~24 kd with strong DNase activities from the culture filtrate of <em>P. carotovorum</em> and a single protein of ~40 kd with a moderate level of DNase activities from culture filtrate of pea root tips. Genes coding for both the <em>P. carotovorum</em> DNase and the pea DNase have been identified by Orbitrap LC-MS/MS. As mammalian DNase II is known to play a role in the degradation of exogenous DNA encountered by phagocytosis, the defensive role of pea exDNase is anticipated.</div>