Proteomic Analysis Identifies Dysregulated Proteins in Butanol-Tolerant Gram-Positive Lactobacillus mucosae BR0713-33

Butanol can be produced biologically through fermentation of lignocellulosic biomass-derived sugars by Gram-positive Clostridium species. For cost-effective production, increased butanol fermentation titers are desired. However, the currently available butanol-fermenting microbes do not tolerate sufficiently high butanol concentrations; thus, new butanol-tolerant strains are desired. One promising strategy is to genetically modify Clostridium species by introducing stress tolerance-associated genes. This study was aimed to seek butanol tolerance genes from other Gram-positive species, which might be better suited than those from Gram-negative E. coli or eukaryotic Saccharomyces cerevisiae. Several butanol-tolerant lactobacilli were reported previously, and Lactobacillus mucosae BR0713-33, which showed the most robust anaerobic growth in 4% butanol, was used here for proteomics analyses. Cellular proteins that responded to 2, 3, and 4% butanol were characterized. Twenty-nine proteins that were identified were dysregulated in response to increased concentrations of butanol in L. mucosae . Seventeen genes involved in coding for stress-tolerant proteins GroES, GroEL, and DnaK and genes involved in substrate utilization, fatty acid metabolism, and nucleotide synthesis were induced by increased butanol, and 12 genes involving energy production (F₀F₁ATP synthases) and redox balance preservation were repressed by increased butanol. These results can help guide targeted engineering strategies to improve tolerance and production of biobutanol.