Harnessing Robustness of Thermophilic Bacillus coagulans for Conversion of Switchgrass Hydrolysates to Designer Bioesters at Elevated Temperatures
1University of Tennessee; 2National Center for Agricultural Utilization Research, USDA-ARS, Peoria, IL; 3Oak Ridge National Laboratory
To fundamentally understand and redirect metabolism and regulation of thermophilic Bacillus coagulans for the efficient conversion of undetoxified lignocellulosic biomass hydrolysates into designer bioesters.
B. coagulans is a gram-positive thermophilic bacterium that is capable of growing at elevated temperatures, utilizing biomass hydrolysates, and producing lactate at high levels. Researchers aim to understand and harness its robustness for conversion of biomass hydrolysates to designer bioesters (e.g., acetate esters, lactate esters) that have broad use as solvents, flavors, fragrances, and advanced biofuels. Through comprehensive screening of diverse undomesticated B. coagulans strains isolated from different environmental niches against a wide range of temperatures (30-60oC), either single or mixed C5/C6/C12 sugars, and lactate concentrations (0–60 g/L), researchers found that most of the strains could grow in all of the environments tested with different degrees of robustness. Some candidates could utilize all sugars with minimal exhibition of diauxic growth, grow optimally at 55oC, and tolerate high concentrations of lactate up to at least 40 g/L, which serve as reference strains for elucidating cellular robustness and metabolic engineering. Genome sequencing and proteomics of the representative strain UT-1 showed that it has a 10% larger genome than those reported in literature and exhibited metabolic capability to utilize sugars in biomass hydrolysates and produce lactate. To rewire the metabolism of these novel undomesticated B. coagulans strains to overproduce designer bioesters, researchers have been developing genetic tools (e.g., antibiotic selection, plasmid compatibility, transformation, and gene expression) to manipulate them. The team has identified and designed thermostable enzymes to build exchangeable ester production modules compatible with B. coagulans for biosynthesis of acetate and lactate esters. Overall, B. coagulans is a promising microbial manufacturing platform that will be advanced by a fundamental understanding of its robustness and the ability to harness it for production of designer bioesters from lignocellulosic hydrolysates.
Lee, J., et al. 2021. “Probing Specificities of Alcohol Acyltransferases for Designer Ester Biosynthesis with a High-Throughput Microbial Screening Platform,” Biotechnol Bioeng, 1-13.
Lee, J. and C.T. Trinh. 2021. “Controlling Selectivity of Modular Microbial Biosynthesis of Butyryl-CoA-Derived Designer Esters,” Metab Eng 69, 262–74.
Lee, J. and C.T. Trinh. 2020. “Towards Renewable Flavors, Fragrances, and Beyond,” Curr Opin Biotechnol 61, 168–80.
Lee, J. and C.T. Trinh. 2019. “Microbial Biosynthesis of Lactate Esters,” Biotechnol Biofuels 12(1), 226.
Seo, H., et al. 2021. “Repurposing Chloramphenicol Acetyltransferase for a Robust and Efficient Designer Ester Biosynthesis Platform,” Metab Eng 66, 179–90.
This work is supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Genomic Science Program under Award Number DE-SC0022226