Biosynthesis of Cholesterol in an Insect, Silverfish (Ctenolepisma sp.)

Abstract

MUCH nutritional^1–4 and biochemical^5,6 evidence suggests that the insects, as a phylum, are incapable of synthesizing sterols. This biosynthetic deficiency results, in general, in a dietary requirement of insects for some sterol without which they cannot grow to maturity. The apparent capacity of two species to thrive on a sterol-free diet has been shown to reflect the sterol-synthesizing activity of their intestinal micro-organisms which supply sterols (as well as vitamins of the B group) in quantities sufficient to satisfy the insects' growth requirements⁷. Similarly, in the cockroach, Blattella germanica, incorporation of dietary [1-¹⁴C] acetate into sterol, which occurs under non-aseptic conditions, has been shown to be almost entirely abolished in insects reared aseptically⁶. It has been shown that the sterol synthesis observed in this insect under non-aseptic conditions is due to initial synthesis of ergosterol by the intestinal flora, followed by the conversion of this compound to 22-dehydrocholesterol in the tissues of the insect. The rate of formation of 22-dehydrocholesterol by this process is, however, not sufficient to render the cockroach independent of a supply of sterol in its food⁸.