3-48: Metabolic analysis of Lactobacillus rhamnosus under suspended and immobilised conditions

Monday, April 29, 2013
Exhibit Hall
Hendrik G. Brink and Willie Nicol, Chemical Engineering, University of Pretoria, Pretoria, South Africa
The objective of the study was to compare the metabolic flux of the bacterium L. rhamnosus ATCC 9595 in a suspended cell reactor to that of a homogeneous shear biofilm reactor.  Lactic acid (HLac), propionic acid (HProp) and biomass (X) were the only products observed in appreciable quantities.  The carbon distributions (YS,HLac: YS,HProp: YSX) of the reactors were determined to be 0.782:0.102:0.117 for the suspended cell reactor and 0.817:0.074:0.109 for the biofilm reactor.  The improvement in carbon flux towards the desired product (HLac) in the biofilm reactor can be attributed to a 2.5 fold increase in non-growth related production (maintenance) which reduces the carbon flux to X (YSX). The increased maintenance reduces the requirement for ATP generated in the formation of HProp which correspondingly reduces the carbon flux to HProp (YS,HProp).  The consumption of yeast extract throughout the experiment was determined to remain constant irrespective of the dilution rate.  The enhanced volumetric productivity of the biofilm reactor is therefore not only a function of the increased biomass present in the reactor but also a function of the shift in carbon flux.