Abstract
Plasmid‐harbouring, sterol‐decomposing organism Arthrobacter oxydans 317 was treated with sodium dodecylsulphate to obtain a plasmid‐cured strain A. oxydans 317 A1 incapable of utilizing 4‐androstene‐3,17‐dione (AD). The strain 317 Al was unable to degrade β‐sitosterol side chain completely to form AD but could carry out partial degradation as shown by the accumulation of 3‐oxochol‐4‐en‐24‐oic acid as a major metabolite and 27‐norcholest‐4‐en‐3,24‐dione as a minor metabolite. The strain could form 1,4‐androstadiene‐3,17‐dione (ADD) from 3‐oxo‐23,24‐bisnorchol‐1,4‐dien‐22‐oic acid (BNC) to a limited extent. The existence of metabolic blocks in the conversion of 3‐oxochol‐4‐en‐24‐oic acid to 3‐oxo‐23,24‐bis‐norchol‐4‐en‐22‐oic acid and further conversion to AD by the plasmid‐cured strain 317 Al was suggested. Neither the formation of ADD from AD nor the conversion of AD and ADD to 9α‐hydroxy derivatives leading to steroid ring opening could be done by the plasmid‐cured strain but the 17β‐reduction of AD and ADD and 1(2)‐reduction of ADD were not affected by the absence of the plasmid. It was proposed that plasmid determines 1(2)‐dehydrogenation and 9α‐hydroxylation of steroid ring structure in this organism.