Activity and structural characteristics of steroid and non-steroid lipid growth factors for Haliphthoros milfordensis, a fungal parasite of marine crustaceans

Abstract

The lipid growth factor requirement of Haliphthoros milfordensis was satisfied by a number of steroids. Active steroids had a side chain of 8–10 carbons. The stereochemistry at C-5 had to be 5 α when no C-5(6) double bond was present. An oxygen function at C-3 could be either 3β-OH, 3α-OH, 3-keto, or an esterified 3β-OH group. Absence of double bonds in the steroid nucleus and side chain or presence of one or more double bonds at C-4(5), C-5(6), C-7(8), C-8(9), C-22(23), C-24(25) and C-24(28) had no pronounced influence on the activity of the steroid as a growth factor. An additional oxygen function in or at the steroid nucleus or at the side chain retarded or completely inhibited growth of H. milfordensis . The tetracyclic hydrocarbon 5α-cholestane, the phospholipid Lα-lecithin (distearoyl) and the unsaturated fatty acids oleic acid and palmitoleic acid were also active as growth factors. Steroid precursors mevalonic acid, geraniol, farnesol, and squalene were inactive, whereas the cyclization product of squalene-2, 3-epoxide, lanosterol, was active. Indirect evidence for the participation of the growth factors in membrane architecture of H. milfordensis was obtained from studies on the sensitivity of the fungus towards polyene-antibiotics. Steroid-grown cultures were sensitive to nystatin whereas steroid-free oleic acid-grown cultures were not.