Effect of carbon source and concentration on the molecular mass of poly(3-hydroxybutyrate) produced by Methylobacterium extorquens and Alcaligenes eutrophus

Abstract

In shake-flask culture, Methylobacterium extorquens accumulated poly(3-hydroxybutyrate) (PHB) possessing a substantially higher weight-average molecular mass (MW) than previously reported for this organism. The MW of PHB produced by M. extorquens was dependent on the initial concentration of methanol or sodium succinate, used as sole carbon sources. The highest MW values (0.6 and 1.7 × 106) were obtained with low initial concentrations of methanol or sodium succinate (4.0 and 3.0 g l−1, respectively) and the latter substrate always yielded PHB of higher MW than that produced from methanol. Thus PHB with an MW in the range 0.2–1.7 × 106 could be produced by selection of the carbon source and its concentration. In contrast to the findings with M. extorquens, the MW of PHB produced by Alcaligenes eutrophus was high (1.1–1.6 × 106) and generally unaffected by the choice or concentration of the carbon source. The use of glycerol as sole carbon source did, however, result in the accumulation of PHB with a markedly lower MW (5.5–8.5 × 105) than that produced from other sole carbon sources by this organism under similar conditions.