Strategies for fighting Aspergillus flavus

Scientists Probe Yeast's Ability to Protect Tree Nuts

U.S. Department of Agriculture (USDA) scientists have moved a step closer to understanding the underlying mechanisms that enable a helpful yeast to disable a mold that attacks tree nuts such as almonds, pistachios, and walnuts. Their on going laboratory studies may help improve the effectiveness of the yeast, Pichia anomala, in thwarting the mold, A. flavus. The mold is of concern because it can produce aflatoxin, a natural carcinogen.Federal food safety standards, and quality control procedures at U.S. packinghouses, help ensure that tree nuts remain safe to eat. Nonetheless, growers and processors have a continuing interest in new, environmentally friendly ways to combat the A. flavus mold.In an experiment, the mold was exposed to the yeast, and, later, to several different compounds that fluoresce a distinctive red, or green, when evidence of specific changes in the mold's cells is detected. Results of these fluorescence assays, suggest that the yeast interfered with the mold's energy generating ATP system, vital for the mold's survival. The findings also suggest that the yeast damaged mold cell walls and cell membranes. Walls and membranes perform the essential role of protecting cell contents.In other work that has helped pave the way to current studies, the team used a different analytical procedure quantitative reverse transcriptase PCR (polymerase chain reaction) assays to analyze the activity of certain P. anomala genes in the presence of the mold. Preliminary findings, reported at the annual national meeting of the American Society for Microbiology in 2010, suggest that exposing the yeast to the mold may have triggered the yeast to turn on genes that code for production of two enzymes PaEXG1 and PaEXG2. These enzymes are capable of degrading the mold's cell walls and causing damage to membranes.Though further studies are needed, these early, PCR-based findings point to gene-controlled mechanisms that may be involved in the cell wall and cell membrane damage observed in the fluorescence assays.

Fuente: www.ars.usda.gov

Aporte: María Rene Rey