EFFECT OF CARBON SOURCE ON THE FORMATION OF POLYHYDROXYALKANOATES (PHA) BY A PHOSPHATE-ACCUMULATING MIXED CULTURE

In the present work, attention was devoted to understand how different carbon substrates and their concentration can influence the productio n of PHA by polyphosphate-accumulating bacteria. Acetate, propionate, and butyrate were tested independently. The composition of the polymer s formed was found to vary with the substrate used. Acetate leads to t he production of a copolymer of hydroxybutyrate (HB) and hydroxyvalera te (HV) with the HE units being dominant. With propionate, HV units ar e mainly produced and only a small amount of HE is synthesized. When b utyrate is used, the amount of polymer formed is much lower with the H B units being produced to a higher extent. The yield of polymer produc ed per carbon consumed (Y-P/S) was found to diminish from acetate (0.9 7) to propionate (0.61) to butyrate (0.21). Using a mixture of acetate , propionate, and butyrate and increasing the carbon concentration, al though maintaining the relative concentration of each substrate, propi onate is primarily consumed and consequently, PHA synthesized was enri ched in HV units. The polymers obtained in all experiments were copoly mers with the average molecular weight of the most representative frac tion higher when hydroxybutyrate units were present in considerable am ounts. All the polymers synthesized were found to be quite homogeneous and their average molecular weight is of the same order of magnitude as the ones commercially available. (C) 1998 Elsevier Science Inc.