3-Deoxy-2-octulosonidase (, 2-keto-3-deoxyoctonate hydrolase, octulosylono hydrolase, octulofuranosylono hydrolase, octulopyranosylonohydrolase) is an enzyme with systematic name capsular-polysaccharide 3-deoxy-<small>D</small>-manno-2-octulosonohydrolase. This enzyme catalyses the following chemical reaction
The bacteriophage enzyme depolymerizes polysaccharides containing 3-deoxy-2-octulosonide in the cell wall of Escherichia coli.