Involved in the degradation of galactose via the DeLey-Doudoroff pathway. Catalyzes the reversible, stereospecific retro-aldol cleavage of 2-keto-3-deoxy-6-phosphogalactonate (KDPGal) to pyruvate and D-glyceraldehyde-3-phosphate. In the synthetic direction, it catalyzes the addition of pyruvate to electrophilic aldehydes with re-facial selectivity. It can use a limited number of aldehyde substrates, including D-glyceraldehyde-3-phosphate (natural substrate), D-glyceraldehyde, glycolaldehyde, 2-pyridinecarboxaldehyde, D-ribose, D-erythrose and D-threose. It efficiently catalyzes aldol addition only using pyruvate as the nucleophilic component and accepts both stereochemical configurations at C2 of the electrophile. 2-dehydro-3-deoxy-6-phospho-D-galactonate = D-glyceraldehyde 3-phosphate + pyruvate kcat is 4 sec(-1) for KDPGal. Carbohydrate acid metabolism; D-galactonate degradation; D-glyceraldehyde 3-phosphate and pyruvate from D-galactonate: step 3/3. Homotrimer. Part of the dgoRKADT operon, which encodes proteins for the metabolism of D-galactonate (PubMed:30455279). Negatively regulated by DgoR (PubMed:30455279). Expression is induced in the presence of D-galactonate and galactose (PubMed:30455279, PubMed:324806). Deletion mutant cannot grow on D-galactonate. Belongs to the KHG/KDPG aldolase family. The frameshift in position 204 caused the prediction of an ORF that fused dgoA and dgoD.