Succinic acid production with Actinobacillus succinogenes : rate and yield analysis of chemostat and biofilm cultures

摘要

BACKGROUND: Succinic acid is well established as bio-based platform chemical with production quantities expectingto increase exponentially within the next decade. Actinobacillus succinogenes is by far the most studied wild organismfor producing succinic acid and is known for high yield and titre during production on various sugars in batch culture.At low shear conditions continuous fermentation with A. succinogenes results in biofilm formation. In this study, anovel shear controlled fermenter was developed that enabled: 1) chemostat operation where self-immobilisationwas opposed by high shear rates and, 2) in-situ removal of biofilm by increasing shear rates and subsequentanalysis thereof.RESULTS: The volumetric productivity of the biofilm fermentations were an order of magnitude more than thechemostat runs. In addition the biofilm runs obtained substantially higher yields. Succinic acid to acetic acid ratiosfor chemostat runs were 1.28±0.2 g.g-1, while the ratios for biofilm runs started at 2.4 g.g-1 and increased up to 3.3 g.g-1as glucose consumption increased. This corresponded to an overall yield on glucose of 0.48±0.05 g.g-1 for chemostatruns, while the yields varied between 0.63 g.g-1 and 0.74 g.g-1 for biofilm runs. Specific growth rates (μ) were shownto be severely inhibited by the formation of organic acids, with μ only 12% of μmax at a succinic acid titre of 7 g.L-1.Maintenance production of succinic acid was shown to be dominant for the biofilm runs with cell based productionrates (extracellular polymeric substance removed) decreasing as SA titre increases.CONCLUSIONS: The novel fermenter allowed for an in-depth bioreaction analysis of A. succinogenes. Biofilm cellsachieve higher SA yields than suspended cells and allow for operation at higher succinic acid titre. Both growth andmaintenance rates were shown to drastically decrease with succinic acid titre. The A. succinogenes biofilm process hasvast potential, where self-induced high cell densities result in higher succinic acid productivity and yield.