title: Succinic acid-producing biofilms of Actinobacillus succinogenes: reproducibility, stability and productivity.
abstract: Continuous anaerobic fermentations were performed in a biofilm reactor packed with Poraver® beads. Dilution rates (D) varied between 0.054 and 0.72 h(-1), and D-glucose and CO2 gas were used as carbon substrates. Steady-state conditions were shown to be repeatable and independent of the operational history. Production stability was achieved over periods exceeding 80 h at values of D below 0.32 h(-1). In these situations, steady-state variation (expressed as fluctuations in NaOH neutralisation flow rates) exhibited a standard deviation of less than 5 % while no indication of biofilm deactivation was detected. The total biomass amount was found to be independent of the dilution rate with an average dry concentration of 23.8 ± 2.9 g L(-1) obtained for all runs. This suggests that the attachment area controls the extent of biofilm accumulation. Specific succinic acid (SA) productivities, based on the total biomass amount, exhibited a substantial decrease with decreasing D. An SA volumetric productivity of 10.8 g L(-1) h(-1) was obtained at D = 0.7 h(-1)-the highest value reported to date in Actinobacillus succinogenes fermentations. SA yields on glucose increased with decreasing D, with a yield of 0.90 ± 0.01 g g(-1) obtained at a D of 0.054 h(-1). Production of formic acid approached zero with decreasing D, while the succinic to acetic acid ratio increased with decreasing D, resulting in an increasing SA yield on glucose.
authors.affiliation: Department of Chemical Engineering, University of Pretoria, Lynnwood Road, Private Bag X20, Hatfield, 0002, Pretoria, South Africa, karishma.maharaj@gmail.com.
authors.forename: K
authors.initials: K
authors.lastname: Maharaj
authors.forename: M F A
authors.initials: MF
authors.lastname: Bradfield
authors.forename: W
authors.initials: W
authors.lastname: Nicol
mesh_terms: D000188:Actinobacillus / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D000693:Anaerobiosis; D001422:Bacterial Adhesion; D018441:Biofilms / Q000254:growth & development*; D018533:Biomass; D002245:Carbon Dioxide / Q000378:metabolism; D005561:Formates / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D019802:Succinic Acid / Q000378:metabolism*
chemical_list: D005561:Formates; C030544:formic acid; D002245:Carbon Dioxide; D019802:Succinic Acid; D005947:Glucose