Selection of Mycobacterium sp strains with capacity to biotransform high concentrations of beta-sitosterol

In this work, phytosterol-biotransforming strains were selected from Mycoba cterium sp., using a high concentration of beta -sitosterol. The selection was made by culturing the strains in a medium enriched with 14 g beta -sito sterol/l as the unique source of carbon. During 2 months, the bacterial cul tures were transferred successively. The extraction of the biotrans formati on products was made with methanol and ethyl acetate. The qualitative and q uantitative analysis was made by means of thin-layer chromatography, gas-li quid chromatography (GLC) and GLC-mass spectrometry. Under these conditions , it was observed that after seven transfers, the strains Mycobacterium sp. MB-3683 and the Mycobacterium fortuitum B-11045 increased their biotransfo rmation capacity from 20% to 64% and from 34% to 55%, respectively. The pro ducts in the highest proportion identified for each trial were androstenedi one and androstadienedione. The results suggest that the high substrate con centration could be a selective mechanism to obtain strains more efficient in the biotransformation of beta -sitosterol into steroidal bases.