Aflatoxin and Sclerotial Production byAspergillus flavus: Influence of pH

Abstract

Sodium nitrate and ammonium sulfate have different influences on aflatoxin and sclerotial production when used as sole nitrogen sources in solid media. The effects are attributable, at least in part, to pH. Ammonium-based media became acidified during culture while aflatoxin production increased, and sclerotial production was totally inhibited. Sclerotia were producted on buffered ammonium media. Sclerotial production increased with increased pH on buffered ammonium media while aflatoxin production declined; aflatoxin was not produced after sclerotial maturation (5 days of incubation). Aflatoxin B1 concentrations declined in acidic ammonium media, whereas aflatoxin B2 remained stable. Nitrate-based media pH increased with fungal growth and production of large quantities of sclerotia and low concentrations of aflatoxin. Lowering nitrate media pH during culture with exogenous HCl totally inhibited sclerotial production and increased aflatoxin production than those produced on ammonium media. Results suggest a pH-mediated, interrelated regulation of sclerotial morphogenesis, and aflatoxin biosynthesis.