Calorimetrically recognized maximum yield of poly-3-hydroxybutyrate (PHB) continuously synthesized from toxic substrates

The broader usage of poly-beta-hydroxybutyrate (PHB), for instance as bulk plastics, calls for cheap raw materials and greater overall process efficie ncy. The bacterial synthesis is generally induced and promoted by the limit ation of growth via nitrogen, oxygen or phosphate depletion with the simult aneous excess and higher concentration of the carbon substrate. Consequentl y, toxic substrates have been considered unsuitable for PHB synthesis. Neve rtheless, a single-stage continuous process for producing PHB from toxic su bstrates using microorganisms was developed and is reported here. The maxim um heat flux during continuous growth and the maximum yield of PHB versus t he substrate consumption rate were found to coincide. This suggests the pos sibility of controlling the conversion of a growth-inhibiting substrate int o PHB and maximizing the process efficiency. The observed correlation occur red irrespective of the substrates investigated (phenol or sodium benzoate) , the PHB-producing strain (Ralstonia eutropha JMP 134 or Variovorax parado xus JMP 116), or the type of limitation imposed. The maximum PHB yields obt ained comprised up to 50% of cell dry mass. (C) 2000 Elsevier Science B.V. All rights reserved.