Proteomic analysis to elucidate degeneration of Clostridium beijerinckii NCIMB 8052 and role of Ca²⁺ in strain recovery from degeneration

Degeneration of solventogenic Clostridium strains is one of the major barriers in bio-butanol production. A degenerated Clostridiumbeijerinckii NCIMB 8052 strain (DG-8052) was obtained without any genetic manipulation. Supplementation of CaCO₃ to fermentation medium could partially recover metabolism of DG-8052 by more than 50 % increase of cell growth and solvent production. This study investigated the protein expression profile of DG-8052 and its response to CaCO₃ treatment. Compared with WT-8052, the lower expressed proteins were responsible for disruption of RNA secondary structures and DNA repair, sporulation, signal transduction, transcription regulation, and membrane transport in DG-8052. Interestingly, accompanied with the decreased glucose utilization and lower solvent production, there was a decreased level of sigma-54 modulation protein which may indicate that the level of sigma-54 activity may be associated with the observed strain degeneration. For the addition of CaCO₃, proteomic and biochemical study results revealed that besides buffer capacity, Ca²⁺ could stabilize heat shock proteins, increase DNA synthesis and replication, and enhance expression of solventogenic enzymes in DG-8052, which has a similar contribution in WT-8052.