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

In shake-flask culture, Methylobacterium extorquens accumulated poly(3-hydroxybutyrate) (PHB) possessing a substantially higher weight-average molecular mass (M_W) than previously reported for this organism. The M_W of PHB produced by M. extorquens was dependent on the initial concentration of methanol or sodium succinate, used as sole carbon sources. The highest M_W 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 M_W than that produced from methanol. Thus PHB with an M_W 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 M_W 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 M_W (5.5–8.5 × 10⁵) than that produced from other sole carbon sources by this organism under similar conditions.Correspondence to: A. J. Anderson