Fermentation characteristics in conversion of organic acids obtained by oxidation of low-rank coals to poly(β-hydroxybutyrate) using A. eutrophus cells with some analysis on metabolic flux distribution

Fermentation characteristics are investigated for the conversion of glycolate, acetate, formate, and malonate obtained by the oxidation of low-rank coals to poly(β-hydroxybutyrate) (PHB) using A. eutrophus cells. Based on the cultivation experiments using one of the organic acids as a sole carbon source, it is found that acetate is the most effectively converted to PHB. When mixed organic acids are used, formate is preferentially consumed, followed by acetate, and finally glycolate. Although malate can not be utilized, it is implied that it might change the pathway flux distributions based on the metabolic flux analysis. Namely, it shows competitive inhibition to succinate dehydrogenase so that its addition during fermentation results in flux reduction from succinate to maleic acid as well as glyoxylate flux and gluconeogenesis flux. It is also found that NADPH generated from isocitrate is preferentially utilized for the reaction from α-ketoglutarate to glutamate when NH₃ concentration is high, while it is eventually used for the PHB production from acetoacetyl CoA as NH 3 concentration decreases.