Affiliations: Department of Chemical Engineering, Indian Institute
of Technology Bombay, Powai, Mumbai-400076, India | School of Bioscience & Bioengineering, Indian
Institute of Technology Bombay, Powai, Mumbai-400076, India
Abstract: Quantification of metabolism through elementary modes offers
insights into the working of a metabolic network. We have determined the fluxes
of elementary modes through linear optimization using the stoichiometry of the
elementary modes as a constraint. We apply this methodology to obtain insights
into the effect of preculturing on growth of Lactobacillus rhamnosus on
medium containing mixed substrates. L. rhamnosus, a microaerophilic
organism, produces flavor compounds such as diacetyl and acetoin during growth
on glucose and citrate. The uptake of citrate has been shown to be sensitive to
preculturing states of the cells. Elementary modes demonstrated that citrate
was utilized by the organism as a sole carbon source. Further, both glucose and
citrate was catabolized by this organism through aerobic and anaerobic routes.
The flux analysis indicated that only 21 elementary modes were operational
during growth of L. rhamnosus on glucose and citrate. Glucose
specifically accounted for 6 elementary modes, while the remaining 15 involved
citrate as substrate. The modes associated with glucose were mainly operational
when cells were precultured on glucose. It was observed that all the 21 modes
contributed to the fluxes when the cells were precultured on citrate. The NADH
recycling through lactate formation and oxygen uptake were dependent on the
preculturing state. The analysis also demonstrated that preculturing on citrate
yielded better productivity of diacetyl and acetoin.
Keywords: Elementary modes, linear optimization, Lactobacillus rhamnosus, flavor production, preculturing state
