Aflatoxins formation

The conversion fix>m averufin (AVF) to versiconal hemiacetal acetate (VHA) is catalyzed by an averufin oxidase encoded by afll (oyfA) (41). VHA was converted to versiconal (VAL) by an esterase (29, 63, 64, 65). VAL is converted to Versicolorin B (VERB) by a VERB synthase (31). The gene, qflK (ybs), was cloned, characterized and expressed (66,67,68). It was demonstrated that the versicolorin B synthase catalyzes the side chain cyclodehydration of racemic VHA to VERB. This is a key step in the aflatoxin formation since it closed the bisfuran ring of aflatoxin for binding to DNA. VERB is converted to versicolorin A (VERA) by a desaturase encoded by qflL (verB) (31). 

Table I. Genes Potentially Involved in Aflatoxin Formation Identified...

Relationship Between Phytoalexin Production and Aflatoxin Contamination. Many samples that had lost the capacity for phytoalexin production had no detectable aflatoxin, while in other similar samples aflatoxin levels ranged as high as 2400 ppb (Table I). Significantly however, no sample of peanuts that had moderate to high phytoalexin-producing capacity contained >5 ppb aflatoxin. Therefore, it can be stated that as long as peanut kernels had the capacity for phytoalexin production, aflatoxin was not formed (Table I). However, the loss of phytoalexin-producing capacity resulted in aflatoxin formation but in only a portion of these susceptible kernels (Domer,... 

Schmidt F R, Lemke P A, Esser K (1986). Viral influences on aflatoxin formation by Aspergillus flavus. Appl. Microbiol. Biotechnol. 24 248-252. 

Perhaps the single, most impressive, aflatoxin-related episode reported in recent scientific literature is an acute poisoning in an area of India in 1974 involving over 400 people and resulting in 106 deaths. The circumstances were typical of those highly conducive to excessive mycotoxin exposure, i.e., a poor, rural subsistence economy, where the people were virtually totally dependent on a single food crop (corn, Zea mays L.) that they produced themselves, and conditions were favorable for aflatoxin formation as a result of unseasonable rains that drenched the crop at harvest in the warm subtropical climate of the area. 

Several trace elements are required for aflatoxin formation by A. flavus, particularly zinc (7). The necessity for zinc, magnesium, and other mineral elements for aflatoxin production by... 

Zinc, magnesium, iron and molybdenum were essential, whereas manganese appeared to stimulate aflatoxin formation. 

Most data on the relation of temperature to aflatoxin formation have been obtained with A. parasiticus. Aflatoxin contamination of cottonseed by A. flavus in the field occurs primarily in low-altitude areas of Arizona and the Imperial Valley of California and not in the hot and humid Southeastern States. Chronic field contamination of cottonseed apparently requires daily mean temperature of 34 C or above (T.E. Russell, personal communication). The significant difference between Arizona and the Southeast cotton areas is the high night temperatures of 32-34 C in Arizona. 

These data and those in Table IX emphasize the critical role of temperature in aflatoxin formation in developing corn kernels. 

GENETICS AND BIOCHEMISTRY OF AFLATOXIN FORMATION AND GENOMICS APPROACH FOR PREVENTING AFLATOXIN CONTAMINATION... 

The relationship of carbon source and aflatoxin formation has been well established Simple sugars such as glucose, sucrose, maltose, but not peptone, sorbose, or lactose, support aflatoxin formation. However, the role of carbon in... 

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