The amino acid and humic acid requirements of Saccharothrix algeriensis NRRL B-24137 for growth and production of the dithiolopyrrolone antibiotics were studied in a semi-synthetic medium (SSM). Nature and concentration of amino acids and humic acid strongly influenced the growth and dithiolopyrrolone specific production. The highest value of thiolutin (acetyl-pyrrothine) specific production was obtained in the presence of 1 g/l humic acid (336 mg/g DCW), and in the presence of 5 MM L-cystine (309 mg/g DCW) as compared to 19 mg/g DCW obtained with the control. Furthermore, thiolutin production was increased about six-fold, four-fold and three-fold in the presence Of L-proline, L-glutamic acid and DL-histidine, respectively. In contrast, the production of thiolutin was reduced by addition of other amino acids such as L-glutamine, DL-ethionine, L-methionine and L-arginine. The highest value of isobutyryl-pyrrothine production was obtained in the presence of 2,6-diaminopimelic acid and L-lysine (7.8 and 1.0 mg/g DCW, respectively). However, the highest value of butanoyl-pyrrothine production was obtained in the presence of humic acid (6.6 mg/g DCW), followed by L-cysteine and L-proline (3.6 and 3.2 mg/g DCW, respectively). In addition, the maximum specific production of senecioyl-pyrrothine (29 mg/g DCW) and tigloyl-pyrrothine (21 mg/g DCW) was obtained in the presence of humic acid. We found that, except for isobutyryl-pyrrothine, production of all dithiolopyrrolones was favoured by addition Of L-proline. The maximum specific production was obtained with L-proline at concentrations of 2.50 mM for thiolutin (133 mg/g DCW), 1.25 mM for senecioyl-pyrrothine, tigloyl-pyrrothine and butanoyl-pyrrothine production (29, 23 and 3.9 mg/g DCW, respectively). Production of all dithiolopyrrolones strongly decreased as the L-methionine or DL-ethionine concentration was increased in the culture medium. (c) 2006 Elsevier Inc. All rights reserved.