Submitted to: Fungal Genetics Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: July 1, 2003
Publication Date: October 1, 2003
Citation: Ehrlich, K., Cotty, P.J. 2003. New insights into pH regulation of aflatoxin production by Aspergillus species. XXII Fungal Genetics Conference Proceedings. Abstract No. 201. p. 283. Technical Abstract: Aflatoxins (AF) are toxic and carcinogenic metabolites produced by Aspergillus species. Previous studies found AF production to be pH dependent and, in some cases, pH inhibition and stimulation of AF production was found to override nutritional influences on aflatoxin accumulation. Differential regulation of AF production in ammonia-based media was previously found between West African (SBG) and North American (SB) S strains. We now show that this differential effect results from inhibition at pH 2.5 of toxin production by the three SBG isolates examined. A. parasiticus and SBG isolates produce both B and G aflatoxins. Aflatoxin G production varied more with pH than did aflatoxin B production. No AFG1 was produced at pH 2.5. The AFB1/AFG1 ratio at pH 3.5 was 3.0, whereas at pH 5.5 the ratio was 0.5. Although A. parasiticus isolates produced high levels of AF at both pH 2.5 and 5.5, the AFB1/AFG1 ratio was similarly influenced by pH. Quantitative PCR was used to examine pH influences on expression of six genes involved in AF biosynthesis, including two genes (fasA and pksA) for initial steps, the transcriptional regulator gene (aflR), and three genes for final steps (omt1, ordA, and ordB). For the SBG isolates, expression of most examined genes was inversely proportional to the pH effect on AF accumulation. However, reductions of omt1 expression were paralleled by reductions in aflatoxin production at low pH. For the other isolates, pH effects on gene expression did not correlate with influences on AF accumulation. These results suggest that expression of omt1 may explain a portion of the influence of low pH on aflatoxin production by SBG isolates, but most pH influences do not occur at the level of transcription.