Microbiological agencies in the degradation of steroids; steroid utilization by the microflora of soils.

An investigation of the degradation of cholesterol by soil microorganisms has shown that the initial oxidation of this compound is due, both in situ and in pure culture, to the activities of members of a single genus, Proactinomyces (Turfitt, 1944a). During the cultural work a considerable number of organisms, both molds and bacteria, persisted with the strains of Proactinomyces through many subcultures, but when isolated and inoculated into synthetic medium with cholesterol as sole C source, were unable to survive. Since Proactinomyces oxidation results in the formation of A4-cholestenone, and subsequently in actual molecular fission (Turfitt, 1944b, 1947), it may well be that the further products resulting from Proactinomyces oxidation constituted a substrate for the growth of the attendant organisms. In the case of steroid compounds lacking the intact hydrocarbon C17 side chain, oxidations at -OH groups giving the corresponding keto compounds have been reported with several groups of organisms, Flavobacterium dehydrogenars (Arnaudi, 1942), Flavobacterium androstenedionicum (Ercoli and Molina, 1944), Flavobacterium carbonilicum (Molina and Ercoli, 1944), Alcaligenesfaecalis (Schmidt, Hughes, Green, and Cooper, 1942; Hughes and Schmidt, 1942), Esherichia coli (Schmidt and Hughes, 1944), and pseudodipitheria bacilli (Zimmermann and May, 1944). These investigations, however, have been concerned essentially with ketone formation, and, in general, alternative carbon sources such as serum or yeast water have been included in the cultures with the object of obtaining a vigorous multiplication of the bacterial cells and a consequent high dehydrogenase concentration. Synthetic media with cholic acid as the sole carbon source have been used by Schmidt, Hughes, Green, and Cooper (1942) in oxidations with Alialigenes faecalis, and triketocholanic acid has been isolated as the end product of the bacterial action. In this instance it is clear that the carbon available for growth has been derived from a breakdown of the bile acid molecule. The only general restrictive influence on bacterial utilization thus far reported is due to the side chain, and the available evidence suggests that the modified natural sterol skeleton is probably susceptible to attack by a variety of organ1sms.