Catalyzes the dehydration of D-galactonate to 2-keto-3-deoxy-D-galactonate. D-galactonate = 2-dehydro-3-deoxy-D-galactonate + H2O Binds 1 Mg(2+) ion per subunit. Carbohydrate acid metabolism; D-galactonate degradation; D-glyceraldehyde 3-phosphate and pyruvate from D-galactonate: step 1/3. Part of the dgoRKADT operon, which encodes proteins for the metabolism of D-galactonate (PubMed:30455279). Negatively regulated by DgoR (PubMed:30455279). Induced by galactonate, but not by glycerol, gluconate or galactose (PubMed:324806, PubMed:30455279). Repressed by glucose (PubMed:211976). Deletion mutant cannot grow on D-galactonate. Reaction proceeds via an anti dehydration. Belongs to the mandelate racemase/muconate lactonizing enzyme family. GalD subfamily. The frameshift in position 1 caused the prediction of an ORF that fused dgoA and dgoD.