Characterization and mathematical modeling of growth and glutamic acid production by Bacillus methanolicus MGA3.

摘要

The goal of this thesis was to develop a fundamental understanding of growth and glutamic acid production by Bacillus methanolicus MGA3, a thermotolerant Gram-positive bacterium growing at 50°C on methanol as the sole source of carbon and energy.; A continuous stirred tank reactor was designed to grow the wild type strain B. methanolicus MGA3 under defined steady-state conditions. Using methanol-limitation, the carbon conversion to biomass was in the range of 65% to 75%. Glutamic acid was secreted into the medium at a specific rate of up to 5 mg/(g.h). This rate could be increased by up to two orders of magnitude when switching to magnesium-limitation.; Perturbation studies in continuous culture showed that induced transients in the rate of oxygen supply can cause the carbon dioxide evolution rate to transiently increase by up to 35% compared to steady-state conditions. Pulse additions of methanol to the reactor resulted in partial or complete biomass washout. 13C-NMR and isotope-ratio mass spectrometry methods were developed, and the results of these in vivo experiments provide strong evidence that B. methanolicus MGA3 can oxidize formaldehyde via formate to carbon dioxide. This linear dissimilation pathway was previously unknown to exist in Gram-positive methylotroph bacilli.; A mathematical model was developed that is based on biochemically structured balances describing methanol dissimilation to generate NAD(P)H and ATP as well as assimilation to produce biomass and glutamic acid. Simulations were carried out that improve the understanding of the steady-state carbon flow from methanol to carbon dioxide, biomass, and glutamic acid in B. methanolicus MGA3.