Genomic insights into persistence, antibiotic resistance, and intraspecific diversity of lactic acid bacterial contaminants at corn dry-grind fuel ethanol facilities.

During fuel ethanol production, fermenter tanks are persistently contaminated by lactic acid bacteria (LAB), lowering ethanol yields and causing costly shutdowns for cleaning. In this study, whole-genome sequencing was conducted for 156 Lactiplantibacillus plantarum, Levilactobacillus brevis, Limosilactobacillus fermentum, and Limosilactobacillus mucosae isolates previously obtained in a two-year longitudinal study at a U.S. Midwest corn dry-grind fuel ethanol production facility. Striking similarity between genomes for isolates collected during different years reveal the strong ability of LAB strains to persist in bioethanol fermentation facilities. Furthermore, comparison of bioethanol contaminant genomes and previously published genomes in the same species from other environments showed a smaller, closed pangenome for bioethanol contaminants, indicating their specialization for this niche. Additionally, 39 genomes contained a putative plasmid or transposable element encoding for resistance to the antibiotic virginiamycin, frequently used by fermentation facilities to control LAB contamination. Finally, comparison of L. fermentum isolates that strongly inhibited Saccharomyces cerevisiae fermentation and less inhibitory isolates suggest there may be genetic and metabolic changes underlying these differences. To our knowledge, this study represents the first large-scale genomic analysis for LAB contaminants of bioethanol production, providing new insights into the biology of industrial microbial contaminants that have enormous economic impact.