Purification and structural characterization of fengycin homologues produced by Bacillus subtilis LSFM-05 grown on raw glycerol

Raw glycerol is a byproduct of biodiesel production that currently has low to negative value for biodiesel producers. One option for increasing the value of raw glycerol is to use it as a feedstock for microbial production. Bacillus subtilis LSFM 05 was used for the production of fengycin in a mineral medium containing raw glycerol as the sole carbon source. Fengycin was isolated by acid precipitation at pH 2 and purified by silica gel column chromatography and characterized using electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) with collision-induced dissociation (CID). The mass spectrum revealed the presence of the ions of m/z 1,435.7, 1,449.9, 1,463.8, 1,477.8, 1,491.8 and 1,505.8, which were further fragmented by ESI-MS/MS. The CID profile showed the presence of a series of ions (m/z 1,080 and 966) and (m/z 1,108 and 994) that represented the different fengycin homologues A and B, respectively. Fengycin homologues A and B are variants that differ at position 6 of the peptide moiety, having either Ala or Val residues, respectively. Mass spectrometry analyses identified four fengycin A and three fengycin B variants with fatty acid components containing 14–17 carbons. These results demonstrate that raw glycerol can be used as feedstock to produce fengycin, and additional work should focus on the optimization of process conditions to increase productivity.