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Background  Biodiesel production results in crude glycerol waste from the transesterification of fatty acids (10 % w/w). The solventogenic  Clostridium pasteurianum , an anaerobic Firmicute, can produce butanol from glycerol as the sole carbon source. Coupling butanol fermentation with biodiesel production can improve the overall economic viability of biofuels. However, crude glycerol contains growth-inhibiting byproducts which reduce feedstock consumption and solvent production.    Results  To obtain a strain with improved characteristics, a random mutagenesis and directed evolution selection technique was used. A wild-type  C. pasteurianum  (ATCC 6013) culture was chemically mutagenized, and the resulting population underwent 10 days of selection in increasing concentrations of crude glycerol (80–150 g/L). The best-performing mutant (M150B) showed a 91 % increase in butanol production in 100 g/L crude glycerol compared to the wild-type strain, as well as increased growth rate, a higher final optical density, and less production of the side product PDO (1,3-propanediol). Wild-type and M150B strains were sequenced via Single Molecule Real-Time (SMRT) sequencing. Mutations introduced to the M150B genome were identified by sequence comparison to the wild-type and published closed sequences. A major mutation (a deletion) in the gene of the master transcriptional regulator of sporulation, Spo0A, was identified. A  spo0A  single gene knockout strain was constructed using a double--crossover genome-editing method. The Spo0A-deficient strain showed similar tolerance to crude glycerol as the evolved mutant strain M150B. Methylation patterns on genomic DNA identified by SMRT sequencing were used to transform plasmid DNA to overcome the native  C. pasteurianum  restriction endonuclease.    Conclusions  Solvent production in the absence of Spo0A shows  C. pasteurianum  differs in solvent-production regulation compared to other solventogenic  Clostridium . Growth-associated butanol production shows  C. pasteurianum  to be an attractive option for further engineering as it may prove a better candidate for butanol production through continuous fermentation.    Electronic supplementary material  The online version of this article (doi:10.1186/s13068-015-0408-7) contains supplementary material, which is available to authorized users.

biotechnology for biofuels

Whole-genome sequence of an evolved Clostridium pasteurianum strain reveals Spo0A deficiency responsible for increased butanol production and superior growth