Converts oxalate to formate and CO(2) in an O(2)-dependent reaction. Can also catalyze minor side reactions: oxalate oxidation to produce H(2)O(2), and oxalate-dependent, H(2)O(2)-independent dye oxidations. H(+) + oxalate = CO2 + formate Binds 2 manganese ions per subunit. Optimum pH is 5.0. Homohexamer. Induced by acid pH but not by oxalate (PubMed:10960116). Positively regulated by SigO and its coactivator RsoA (PubMed:18573182). To B.subtilis OxdD.