Studies on the microbial transformations of steroids and the genetic basis of the transformations

Abstract

1. Introduction and objectives Very little is known about the genetic basis for microbial transformations of sterols and steroids. Microbial conversion of abundantly available phytosterols to C-19 steroids is considered a very promising aspect in steroid drug manufacture. As almost all the naturally occurring microorganisms degrade both sterol side chain and steroid nucleus simultaneously it has become necessary to develop method for selective side chain degradation of sterol. In this connection the development of microbial strains with desired properties by restructuring the genetic make up is a promising approach. For this, a better understanding of the genetic determi-nants controlling the metabolic steps in sterol transformation is needed. Degradative plasmids which are responsible for catabolism of a variety of compounds are known. Besides plasmids are well known as useful vectors for introduction of foreign genes. But nothing much is known about the role of bacterial plasmids in sterol transformations. The work presented in the thesis describes the role of plasmids present in Arthrobacter oxydans 317 in sterol transformations through study of plasmid-cured strains and transfor-mant strain containing specific plasmid. 2. Isolation and Characterization of a Strain A. oxydans 317AL Incapable of steroid Ring Degradation By treatment of A. oxydans 317 with acridine orange - a potent plasmid-curing agent, the emergence of strains incapable of utilizing 4-androstene-3,17-dione (AD) was observed, and among these one strain designated as A. oxydans 317AL was selected for study. Whereas the parent strain A. oxydans 317 is capable of growing on AD, 1,4-androstadiene-3,17-dione (ADD) and 9a-hydroxy-4-androstene-3,17-dione (9a-hydroxy AD) as the sole carbon source, the derived strain A. oxydans 317AL could not. It was proposed that the key enzymes viz. steroid 1,2-dehydrogenase and 9a-hydroxy-lase needed for steroid ring opening may be absent in A. oxydans 317AL. Actual assay of steroid 1,2-dehydrogenase activity...