Microbial Ecology

, Volume 52, Issue 1, pp 45–52 | Cite as

Isolation of Bacterial Antagonists of Aspergillus flavus from Almonds

  • Jeffrey D. PalumboEmail author
  • James L. Baker
  • Noreen E. Mahoney


Bacteria were isolated from California almond orchard samples to evaluate their potential antifungal activity against aflatoxin-producing Aspergillus flavus. Fungal populations from the same samples were examined to determine the incidence of aflatoxigenic Aspergillus species. Antagonistic activities of the isolated bacterial strains were screened against a nonaflatoxigenic nor mutant of A. flavus, which accumulates the pigmented aflatoxin precursor norsolorinic acid (NOR) under conditions conducive to aflatoxin production. Using solid and liquid media in coculture assays, 171 bacteria isolated from almond flowers, immature nut fruits, and mature nut fruits showed inhibition of A. flavus growth and/or inhibition of NOR accumulation. Bacterial isolates were further characterized for production of extracellular enzymes capable of hydrolyzing chitin or yeast cell walls. Molecular and physiological identification of the bacterial strains indicated that the predominant genera isolated were Bacillus, Pseudomonas, Ralstonia, and Burkholderia, as well as several plant-associated enteric and nonenteric bacteria. A set of 20 isolates was selected for further study based on their species identification, antifungal phenotypes, and extracellular enzyme production. Quantitative assays using these isolates in liquid coculture with a wild-type, aflatoxin-producing A. flavus strain showed that a number of strains completely inhibited fungal growth in three different media. These results indicate the potential for development of bacterial antagonists as biological control agents against aflatoxigenic aspergilli on almonds.


Aflatoxin Antifungal Activity Aflatoxin Production Aflatoxin Contamination Yeast Cell Wall 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We thank K. Chan and L. Lazo for technical assistance. This work was supported by U.S. Department of Agriculture Agricultural Research Service CRIS project 5325-42000-031-00D.


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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • Jeffrey D. Palumbo
    • 1
    Email author
  • James L. Baker
    • 1
  • Noreen E. Mahoney
    • 1
  1. 1.Plant Mycotoxin Research Unit, Western Regional Research Center, Agricultural Research ServiceU.S. Department of AgricultureAlbanyUSA

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