L-ornithine N(5)-monooxygenase; part of the siderophore biosynthetic pathway (PubMed:16019163). Omphalotus olearius produces ferrichrome A, but no other siderophore has been detected (PubMed:16019163). Ferrichrome A consists of a hexapeptide ring made up of one glycine, two serine, and three N(5)-hydroxyornithine amino acid residues, the latter acylated by trans-(alpha-methyl)-glutaconic acid residues (PubMed:16019163). The biosynthesis of ferrichrome A depends on the hydroxylation of ornithine to N(5)-hydroxyornithine, catalyzed by the monooxygenase omo1 (PubMed:16019163). The second step, the acylation of N(5)-hydroxy-L-ornithine is probably catalyzed by the N-acyltransferase ato1 (PubMed:16019163). Finally, assembly of ferrichrome A is catalyzed by the nonribosomal peptide synthase (NRPS) fso1 (PubMed:16019163). Siderophore biosynthesis; ferrichrome biosynthesis. Belongs to the lysine N-acyltransferase mbtK family.