As important building-block chemicals, organic acids have been widely used in many industries including food, chemical, pharmaceutical, and medical industries. With the increasing concerns on environment and energy, the biosynthesis of organic acids by microorganisms receives ongoing interest. Various substrates and fermentation conditions have been tried to produce organic acids and great achievements has been made. Here we summarize the recent advances about the strain engineering, process optimization, and applications of several important organic acids, including propionic acid, succinic acid, α-ketoglutaric acid, citric acid, 3-hydroxypropionic acid, fumaric acid, and lactic acid. The future development in the green production of organic acids for wider applications was also prospected.

White Biotechnology for Organic Acids

The development of dynamic modelling of microbial populations in bioprocesses is reviewed. In the 1960s Arnold Fredrickson established the theoretical basis of such models, and other researchers have subsequently advanced them. This review explores the relationships that describe cell proliferation and evaluates the importance of the application of flow cytometry to the fundamental parameterisation of the models for their use in bioprocess engineering. The section "Individual-Based Modelling" discusses recent theoretical developments. Delay-differential equations are demonstrated to describe accurately temporal variation of the cell proliferation cycle and specialised approaches and related iconography are applied to stochastic and deterministic modelling of stages of cellular development. Synchronised cultures of the bacterium Cupriavidus necator were prepared and monitored using a flow cytometer. The data obtained demonstrate that cell proliferation could be simulated quantitatively using the developed model.

From Single Cells to Microbial Population Dynamics: Modelling in Biotechnology Based on Measurements of Individual Cells

Process control strategies, e.g. the steady-;state fermation, which do not consider the cell-;state distribution of cell populations, cause a decrease of yield coefficient connected to an increase of heat-;production coefficient.



Contrary to this, the dynamic process control adapts the carbon-;substrate supply to the different repetitive cell-;population states during fermentation. In order to recognize the different states, the cell population is synchronized. The optimum period ofchanging carbon-;substrate supply was found to be dependent on the cell-;doubling time. Dynamic process control causes a higher yield coefficient as well as a lower heat-;production coefficient compared to the steady-;state fermentation.

D. Meyer

Papers

Vol. 8. Microbial degradation. Weinheim: VCH Verlagsgesellschaft, 1986. 725 pp. 217 fig., 104 tab., 495 DM