Microbial contamination of commercial corn-based fuel ethanol fermentations

Abstract Microbial contamination in commercial corn-based fuel ethanol facilities reduces efficiency and profitability. In this study, both bacterial and fungal contamination were quantitated using culture-independent DNA sequencing methods. Five wet mill and five dry grind plants were sampled at multiple process points. Fermentors primarily showed contamination by Lactobacillus with little contamination by fungi. In wet mill facilities, Lactobacillus predominated in steep water, likely a primary source of contamination. However, Lactobacillus was widespread at many process points, offering multiple opportunities for reinfection. In dry grind facilities, yeast propagation tanks, backset water, and combined liquefaction streams were likely sources of contamination. Time-course studies at two dry grind facilities showed that relative abundance of contaminants changed during the fermentations. Cleaning seemed to have little effect on the reoccurrence of contaminants. One dry grind facility was intermittently sampled over a 67-month period. Contaminants showed persistence and stability, but gradually changed in relative abundance over time.