(182e) Hybrid Cybernetic Modeling of Poly-Beta-Hydroxybutyrate Synthesis and Degradation in Cupriavidus Necator

The microbial polyester Poly-beta-hydroxybutyrate (PHB) is an internal energy and carbon reserve material which many microorganisms accumulate when growth is limited by depletion of essential nutrients, e.g. nitrogen. PHB has attracted high industrial and commercial attention since it is a biodegradable thermoplastic and due to its bio-compatible properties even suitable for medical applications [1].

The response of microorganisms to environmental changes is highly regulated and optimized by evolutionary processes. This evolutionary optimization is the basic idea of cybernetic models (CMs), which view the microorganism as an optimal strategist due to evolutionary development. The main advantage of CMs is their moderate complexity compared to detailed dynamic models. Therefore CMs are suitable for nonlinear studies and process control. The framework of CMs was developed by Ramkrishna et. al [2].

There are already CMs for PHB production in Cupriavidus necator available in literature, but either they have neglected degradation of PHB [3] or they have fitted degradation parameters to experiments, which do not include any significant PHB degradation [4,5]. However, previous studies [6] have shown that PHB degradation is crucial for overall dynamic behavior. Therefore, this study will present our experiments, which include both PHB synthesis and degradation and a hybrid cybernetic model will be developed to describe these experimental data.

[1] Yoshiharu Doi, Microbial Polyesters, VCH Publishers Inc.,1990, New York

[2] Ramkrishna D, Kompala DS and Tsao GT. Are Microbes optimal Strategists, Biotechnology Progress (3), p. 121-126, 1987

[3] Yoo S and Kim WS, Cybernetic Model for Synthesis of Poly-beta-hydroxybutyric acid in Alcaligenes eutrophus, Biotechnology and Bioengineering (34), p. 1043-1051, 1994

[4] Gadkar KG and Doyle FJ, Cybernetic Model Predictive Control of a Continuous Bioreactor with Cell Recycle, Biotechnology Progress (19), p. 1487-1497, 2003

[5] Pinto MA and Immanuel CD, Sensitivity of Bifurcation Traits to Model Parameters in Poly-beta-hydroxybutyrate Production: ADCHEM 2-5 April, Brazil, 2006

[6] Franz A, Kybernetische Modellierung der Polyhydroxybutyratbildung in Mikroorganismen, Diploma Thesis, Otto-von-Guericke Universitaet Magdeburg, Germany, 2007