INFLUENCE OF WATER ACTIVITY AND TEMPERATURE ON IN-VITRO GROWTH OF SURFACE CULTURES OF A PHOMA SP. AND PRODUCTION OF THE PHARMACEUTICAL METABOLITES, SQUALESTATINS S1 AND S2

A Phoma sp., known to produce the pharmaceutically active metabolites squalestatin 1 (S1) and squalestatin 2 (S2), was cultured on malt-extr act/agar (MEA) over a range of water activities (a(w), 0,995-0.90) and temperatures (10-35 degrees C) to investigate the influence on growth and metabolite production. Use of the ionic solute NaCl to adjust a(w ) resulted in significantly lower (P < 0.01) squalestatin yields than when the Phoma sp. was grown on MEA amended with the non-ionic solute glycerol. Water activity and temperature and their interactions were h ighly significant factors (P < 0.001) affecting growth of the Phoma sp ., with optimum conditions of 0.998-0.950 a(w) and 35 degrees C. Squal estatin production was similarly influenced by a(w) temperature. time and their interactions (P < 0.001), S1 and S2 production occurred over a narrower a(w) and temperature range than growth, with a slightly lo wer optimum a(w) range of 0.995-0.980 a(w). The optimum temperature fo r squalestatin production varied from 20 degrees C (S1) to 25 degrees C (S2) and yields of S2 were up to 1000 times lower than those of S1. The ratio of S1 and S2 produced by the Phoma sp. was influenced by a(w ) and temperature, with highest values at 0.99-0.95 a(w) and at 15 deg rees C. Incubation times of 25 days gave highest yields of both S1 and S2. Up to 2000-fold increases in squalestatin fields were measured at optimum environmental conditions, compared to the unmodified MEA. Thi s indicates the need to consider such factors in screening systems use d to detect biologically active lead compounds produced by fungi.