Biotechnologie et biomatériaux

Abstrait

Production of polyhydroxybutyrate at low pH from glycerol using Acidiphilium cryptum

Ernesto González

Acidiphilium cryptum is an acidophilic heterotrophic microorganism which has been isolated from mine sites and able to accumulate polyhydroxybutyrate (PHB), a biodegradable polymer with physicochemical properties that resemble pretroleum-based plastics. Although most of studies have used glucose as carbon source, this bacterium can also metabolize glycerol which is a low-cost substrate that can be obtained as subproduct from biodiesel industry. The type strain (DSM2389) was used to test the PHB accumulation in flask cultures.

The strain showed a limited ability to accumulate PHB under standard conditions, achieving 3% (w/w) of PHB accumulation after 65 h when cultured in a semi-defined medium with glucose 3 g L-1. However, the PHB accumulation was increased to 4% and 10% in semi-defined and defined media with glycerol 3 g L-1, obtaining also a decrease in culture time to 48 h and 32 h. The addition of pH buffer to the defined medium limited the pH variation and increased the PHB accumulation to 15% w/w after 32 h. In relation to the buffered defined medium with glycerol 3 g L-1, an increase in the carbon source to 9 and 15 g L-1 increased the accumulation to 35% and 39% and the biomass from 1.6 to 2.8 g L-1 (measured as dry weight biomass), although the culture time is also increased to 96 h. The analysis of glucose and glycerol showed that carbon source was depleted in all cases, excepting when the medium contained 15 g L-1 of glycerol. Since this condition yielded the highest percentage of PHB, carbon limitation is undesirable for PHB accumulation.

Few microorganisms are able to proliferate at pH 2.5-3.5, the obtained information may be used to develop robust processes for PHB production at large scale, which may also be implemented using more productive strains (e.g. DX1-1).