Nonribosomal peptide synthase; 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. Expression is iduced under iron-depleted conditions (PubMed:16019163). NRP synthetases are composed of discrete domains (adenylation (A), thiolation (T) or peptidyl carrier protein (PCP) and condensation (C) domains) which when grouped together are referred to as a single module (By similarity). Each module is responsible for the recognition (via the A domain) and incorporation of a single amino acid into the growing peptide product (By similarity). Thus, an NRP synthetase is generally composed of one or more modules and can terminate in a thioesterase domain (TE) that releases the newly synthesized peptide from the enzyme (By similarity). Occasionally, methyltransferase domains (responsible for amino acid methylation) are present within the NRP synthetase (By similarity). Fso1 has the following architecture: A-T-C-A-T-C-A-T-C-T-C-T-C (PubMed:16019163, PubMed:16502473). Belongs to the NRP synthetase family.