As a result of the metabolic activities of numerous anaerobic microorganisms with sterols, bile acids and steroid hormones as substrates in connection with the enterohepatic circulation of these compounds, the intestine may be considered as an "endocrine" active site or organ. The review summarizes transformations of steroids by anaerobic intestinal bacteria, the physiological and supposed pathophysiological meaning thereof. The aim is to recommend further investigation in this field with respect to both the elucidation of the reactions and biological responses.

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Newly synthesized detergents of polyoxyethylene polyoxypropylene co-polymers (Co-EOPO), polyoxyethylene polyoxypropylene adducts of the diethylene triamine (DETA-EOPO), and steroidal detergents (SDD) stimulate significantly side chain degradation of plant sterols referring to both the sterol degradation and the formation of the product, 9 alpha-hydroxy-androsta-4-ene-3,17-dione (9 OH-AD), by Mycobacterium fortuitum NRRL-B-8119. Highest stimulative effects were observed with derivatives of the DETA-EOPO group. Using compounds of the Co-EOPO group optimal sterol transformation rates were found for polymers with a polyoxypropylene domain of 1400-2000 in molecular weight and with a polyoxyethylene content of 20-50%. Mostly efficient steroidal detergents tested were the 4-cholesten-3-(O-carboxymethyl)-oxime and the amino acid adducts of sterol-3 beta-chlorocarbonates. Detergents were favourably applied as pre-formed sterol-detergent complexes (9:1/w:w) in submers fermentation procedures. By treating harvested resting cells of M. fortuitum with derivatives of Co-EOPO or DETA-EOPO a considerable activation of the cells takes place concerning the sterol degradation and the formation of 9 OH-AD at a high yield in subsequent transformation process on buffer. In solubilization experiments we revealed that there is no correlation between the detergent mediated solubilization of the hydrophobic sterol substrate in the aqueous medium and the transformation activity of the bacterial cells. The detergents are assumed to interact with a multicomponent mesophase (FMCM) which is placed between cells and sterol surface and mediates the transport.