| dc.description.abstract | Isolation, maintenance and identification of microorganisms
are described. A novel method of strain selection is
adopted using a model compound isooctylcyclopentane (I).
Garden soil was treated first with cholesterol and
enrichment was carried out in shake flasks containing
cholesterol and isooctylcyclopentane separately. After
few weeks of enrichment on isooctylcyclopentane, cholesterol
was used for further enrichment. Two organisms were
isolated from the enriched cultures which had the capability
of degrading cholesterol. The organism isolated on
cholesterol was identified to be a Pseudomonas sp. The
other organism isolated on isooctylcyclopentane–cholesterol
was found to belong to the family Neisseriaceae and to the
genus Moraxella.
The fermentation of cholesterol (IIIa), 3,5?cyclocholestane?
6??ol (i?cholesterol) (IIIa), 6??methoxy?3,5?
cyclocholestane (IIIB), 3,5?cyclocholestane?6?one (i?choles?
tanone) (IIIC), 3??methoxy?5?cholestene (IIb), cholesteryl
chloride (IIc), 3??hydroxy?5??cholestane (cholestanol) (IV),
19?hydroxy?3??acetoxy?5?cholestene (V), potassium cholesteryl
sulphate (IId), cholesteryl acetate (IIe) and 3??methoxy?5?
stigmastene (VI) by both Pseudomonas sp. and Moraxella sp.
is described.
The Pseudomonas sp. failed to degrade
any of the substrates described above except cholesterol
and its acetate. With Moraxella sp. two novel transformations
were observed. i?Cholesterol was isomerized back to
cholesterol and 6??methoxy?3,5?cyclocholestane was demethylated
to give i?cholesterol followed by isomerization to
cholesterol. All the other modified substrates were
degraded to the corresponding 17?keto compounds with
varying yields. The advantage of the strain selection
method and the dependence of the side?chain degradability
of the microorganism on the modification of ring structure
are discussed here.
Study of cell?free enzymatic isomerization of
i?cholesterol is the subject of the fourth chapter,
"Partial purification and properties of i?cholesterol
isomerase." The novel transformation of i?cholesterol to
cholesterol, observed in the fermentation of i?cholesterol,
has been studied at the cell?free level.
The enzyme responsible for this isomerization has been
partially purified by ammonium sulphate fractionation.
Various properties of this enzyme are studied.
The fifth and last chapter entitled "Immobilization
of microbial whole cells" describes the fermentation of
19?hydroxycholesteryl acetate (V) and potassium cholesteryl
sulphate (IId) by immobilized whole cells of Moraxella sp.
This chapter starts with an introduction on general methods
of immobilization. Various steroid transformations by
immobilized microorganisms reported to date are reviewed.
Though immobilized cell transformation is known for more
than a decade, relatively few transformations of steroids
are known through immobilized systems. Reports on side?
chain degradation of sterols by immobilized microorganisms
are extremely rare. Two methods of immobilization, i.e.
entrapment and chemical binding on different supports, have
been described. The fermentation of 19?hydroxycholesteryl
acetate with the immobilized cells of Moraxella sp.
resulted in the formation of estrone and potassium
cholesteryl sulphate in dehydroepiandrosterone sulphate,
in a continuous column reactor. Of the various supports
studied agar was found to be the most suitable with more
or less total retention of activity of the free cells. | |
