FIG. 4.

Inhibition of aflatoxin production and growth of A. parasiticus SYS-4 (= NRRL2999) by cyclo(l-Leu-l-Pro) and cyclo(d-Leu-d-Pro) as determined by the tip culture method. (A) A. parasiticus SYS-4 was cultured in YES medium (lanes 1 and 4) or YES medium supplemented with 3.5 mg of cyclo(l-Leu-l-Pro) ml⁻¹ (lanes 2 and 5) or with 3.5 mg of cyclo(d-Leu-d-Pro) (lanes 3 and 6) ml⁻¹ at 28°C for 4 days. The culture medium (lanes 1 to 3) or the mycelial extract (lanes 4 to 6) was analyzed by TLC. (B) A. parasiticus SYS-4 was cultured with various concentrations of cyclo(l-Leu-l-Pro) (○ and □) or cyclo(d-Leu-d-Pro) (• and ▪) at 28°C for 4 days. Wet weight of the mycelia (in milligrams per 250 μl of culture medium) and aflatoxin (AF) production in the culture filtrates were analyzed by HPLC; the values for 100% total aflatoxins were 81.9 ± 6.5 mg ml⁻¹ (□) and 106.7 ± 13.8 mg ml⁻¹ (▪).