Analysis of the Continuous Bioconversion of Glycerol by Promotion of Highly Glycerol-Resistant Glycerol-Degrading Bacteria

Abstract

We identified component microorganisms in a fed-batch operation by modulating the mixed flora via addition of glucose to achieve continuous bioconversion of hardly degradable glycerol. To study the microbial community structure of the flora accumulated by the addition of glucose, 16S ribosomal RNA (rRNA) gene was sequenced using PCR with denaturing gradient gel electrophoresis (DGGE). Burkholderia vietnamiensis, Burkholderia phenoliruptrix, Staphylococcus aureus, Bacillus licheniformis, and Clostridium pasteurianum were identified as component strains. Using the colony containing C. pasteurianum, the hydrogen yield was 0.34 mol/(mol glycerol). C. pasteurianum, B. licheniformis, B. vietnamiensis, and B. phenoliruptrix utilized both glycerol and glucose as substrates and could tolerate high glycerol loads. In early fermentation, predominance of the hydrogen-producing C. pasteurianum resulted in the conversion of glycerol into hydrogen and 1,3-propanediol. In contrast, in late fermentation, the auxiliary degradation of B. licheniformis and the two Burkholderia strains enabled continuous conversion of the glycerol to valuable compounds. Glucose addition results in a stable flora by optimizing the ratio of highly glycerol-resistant glycerol-degrading bacteria, thereby establishing an anaerobic digestion process that allows continuous conversion of high loads of glycerol.