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Anaerobic fermentation of glycerol in Paenibacillus macerans: metabolic pathways and environmental determinants
Ashutosh Gupta1, Abhishek Murarka, Paul Campbell
1Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main Street, MS-362, Houston, TX 77005, USA.
Abstract:
Paenibacillus macerans is one of the species with the broadest metabolic capabilities in the genus Paenibacillus, able to ferment hexoses, deoxyhexoses, pentoses, cellulose, and hemicellulose. However, little is known about glycerol metabolism in this organism, and some studies have reported that glycerol is not fermented. Despite these reports, we found that several P. macerans strains are capable of anaerobic fermentation of glycerol. One of these strains, P. macerans N234A, grew fermentatively on glycerol at a maximum specific growth rate of 0.40 h(-1) and was chosen for further characterization. The use of [U-13C]glycerol and further analysis of extracellular metabolites and proteinogenic amino acids via nuclear magnetic resonance (NMR) spectroscopy allowed identification of ethanol, formate, acetate, succinate, and 1,2-propanediol (1,2-PDO) as fermentation products and demonstrated that glycerol is incorporated into cellular components. A medium formulation with low concentrations of potassium and phosphate, cultivation at acidic pH, and the use of a CO2-enriched atmosphere stimulated glycerol fermentation and are proposed to be environmental determinants of this process. The pathways involved in glycerol utilization and synthesis of fermentation products were identified using NMR spectroscopy in combination with enzyme assays. Based on these studies, the synthesis of ethanol and 1,2-PDO is proposed to be a metabolic determinant of glycerol fermentation in P. macerans N234A. Conversion of glycerol to ethanol fulfills energy requirements by generating one molecule of ATP per molecule of ethanol synthesized. Conversion of glycerol to 1,2-PDO results in the consumption of reducing equivalents, thus facilitating redox balance. Given the availability, low price, and high degree of reduction of glycerol, the high metabolic rates exhibited by P. macerans N234A are of paramount importance for the production of fuels and chemicals.
Insights
Paenibacillus macerans N234A ferments glycerol into ethanol and 1,2-propanediol, important for biofuel production. Environmental factors like low potassium and phosphate stimulate this metabolic capability.
Area of Science:
- Microbiology and Biotechnology
- Metabolic Engineering
Background:
- Paenibacillus macerans possesses broad metabolic capabilities, but glycerol fermentation is poorly understood.
- Previous studies suggested P. macerans does not ferment glycerol, contrasting with our findings.
Purpose of the Study:
- To investigate and characterize glycerol fermentation in P. macerans.
- To identify fermentation products and metabolic pathways involved in glycerol utilization.
Main Methods:
- Utilized [U-13C]glycerol and nuclear magnetic resonance (NMR) spectroscopy for metabolite and amino acid analysis.
- Employed enzyme assays and analyzed extracellular metabolites to elucidate metabolic pathways.
- Investigated the impact of environmental factors on glycerol fermentation.
Main Results:
- Several P. macerans strains, including N234A, were confirmed to ferment glycerol anaerobically.
- Identified ethanol, formate, acetate, succinate, and 1,2-propanediol (1,2-PDO) as fermentation products.
- Demonstrated glycerol incorporation into cellular components and identified key metabolic pathways.
Conclusions:
- Glycerol fermentation in P. macerans N234A is stimulated by low potassium/phosphate, acidic pH, and CO2-enriched atmosphere.
- Synthesis of ethanol and 1,2-PDO are key metabolic determinants, with ethanol production yielding ATP and 1,2-PDO aiding redox balance.
- High metabolic rates in P. macerans N234A make it valuable for sustainable fuel and chemical production from glycerol.
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