Continuous succinic acid production from xylose by Actinobacillus succinogenes

Abstract

) and carbohydrate consumption rates were similar. Also, mass balance closures on xylose were up to 18.2% lower than those on glucose. A modified HPLC method revealed pyruvic acid excretion at appreciable concentrations (1.2 -) which improved the mass balance closure by up to 16.8%. Furthermore, redox balances based on the accounted xylose consumed and the excreted metabolites, indicated an overproduction of reducing power. The oxidative pentose phosphate pathway was shown to be a plausible source of the additional reducing power.

The pentose phosphate pathway leads to enhanced succinic acid flux in biofilms of wild-type Actinobacillus succinogenes

“…Similar to previous continuous, biofilm studies on A. succinogenes Bradfield and Nicol, 2016;Brink and Nicol, 2014;Maharaj et al, 2014), in the current study, the succinic acid yield on substrate ( Figure 2A) and the ratio of succinic acid to acetic acid (Y AASA ; Figure 2B) increased with increasing succinic acid titre (C SA ). Furthermore, the formic acid-to-acetic acid ratio (Y AAFA ) decreased with increasing C SA ( Figure 2B), indicating increased pyruvate-or formate dehydrogenase activity It has been suggested that these trends are linked to a titre-dependent shift in metabolism from a growth to a non-growth or stationary mode Brink and Nicol, 2014), with associated incomplete closures of mass and redox balances.…”

“…As a result, less biofilm was present in the fermenter compared to previous fermentations using a similar fermentation setup Bradfield and Nicol, 2016;Maharaj et al, 2014).…”

“…Independent fermentations on glucose and xylose were performed at dilution rates between 0.02 and 0.3 h -1 in a custom, externally-recycled bioreactor, similar to that used in Bradfield and Nicol (2016). The range of dilution rates allowed for four distinct steady-states (i.e.…”

“…Steady-state conditions were based on constant metabolite concentrations over time and a flat time-averaged NaOH dosing profile, as described in Bradfield and Nicol (2016 were performed in duplicate to show repeatability of fermentation performance. The duplicate sets occurred at the beginning and end of the fermentation.…”

“…Mass and redox balances were performed as described in Bradfield and Nicol (2016) and summarized here for convenience. To determine mass balance closures, the stoichiometric amount of substrate required to produce the measured metabolite concentrations based on elemental balances was compared to the actual amount of substrate consumed.…”