Diversity of thermophilic and thermotolerant fungi in corn grain

ABSTRACT

Corn bins in the midwestern United States can reach temperatures up to 52 C. High temperatures combined with sufficient moisture and humidity in bins provide the perfect environment to promote the growth of thermophilic and thermotolerant fungi. In this article, we characterize for the first time thermophilic and thermotolerant fungi in corn grain bins using culture-based methods and pyrosequencing techniques. Corn samples were collected from local farms in western Illinois. Samples were plated and incubated at 50 C using a variety of approaches. Of several hundred kernels examined, more than 90% showed colonization. Species identified using culture methods included Thermomyces lanuginosus, Thermomyces dupontii, Aspergillus fumigatus, Thermoascus crustaceus, and Rhizomucor pusillus. Pyrosequencing was also performed directly on corn grain using fungal-specific primers to determine whether thermophilic fungi could be detected using this technique. Sequences were dominated by pathogenic fungi, and thermophiles were represented by less than 2% of the sequences despite being isolated from 90% of the grain samples using culturing techniques. The high abundance of previously undocumented viable fungi in corn could have negative implications for grain quality and pose a potential risk for workers and consumers of corn-derived products in the food industry. Members of the Sordariales were absent among thermophile isolates and were not represented in nuc rDNA internal transcribed spacer (ITS) sequences. This is in striking contrast with results obtained with other substrates such as litter, dung, and soils, where mesophilic and thermophilic members of the Sordariaceae and Chaetomiaceae are common. This absence appears to reflect an important difference between the ecology of Sordariales and other orders within the Ascomycota in terms of their ability to compete in microhabitats rich in sugars and living tissues.

KEYWORDS:

• Aspergillus
• Thermomyces
• thermophiles
• organic toxic dust syndrome

ACKNOWLEDGMENTS

We would like to thank the farmers in western Illinois who donated the samples and Marina Small and Antonio Rosales for their help processing them. We acknowledge technical support from the University of New Mexico (UNM) Department of Biology’s Molecular Biology Facility. We thank the UNM Center for Advanced Research Computing for providing high-performance computing resources used in this work.

Additional information

Funding

This project was partially supported by Western Illinois University Graduate Student Research and Professional Development Award and the Department of Biological Sciences. The University of New Mexico (UNM) Department of Biology’s Molecular Biology Facility is supported by National Institutes of Health grant P30GM110907. The UNM Center for Advanced Research Computing is supported in part by the National Science Foundation. This material is based upon work supported by the National Science Foundation (APA). Any opinion, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.