ABSTRACT
Living organisms are major sources of new biologically active molecules for the pharmaceutical, animal health and agrochemical industries. The screening of microbes, plants and animals for biologically active compounds has been a critical part of new drug discovery and development throughout this century. For example, about 13 500 naturally occurring antibiotics are known. Of these, 5500 are produced by actinomycetes, while about 3300 are produced by higher plants and about 90 are in current medical use (Berdy, 1989). These natural products serve not only as drugs in their own right, but they may also serve as structural models for the creation of synthetic analogues, and as models in structure-activity studies (e.g. Quinn et al., 1993). There is an urgent need to discover new biologically active molecules as the rate of discovery of new 'lead' compounds has decreased steadily over the past few decades (cf. Omura, 1992). The microalgae are one exciting source of such new leads.
