EFFECT OF OLIGOSACCHARIDES ON GLUCOSE CONSUMPTION BY RHODOBACTER-SPHAEROIDES IN POLYHYDROXYALKANOATE PRODUCTION FROM ENZYMATICALLY TREATED CRUDE SAGO STARCH

A method of producing a bacterial polyester, polyhydroxyalkanoate (PHA ), from enzymatically treated crude sage starch using the photosynthet ic bacterium Rhodobacter sphaeroides (IFO 12203) is described. When a- amylase and glucoamylase were used in sequence to saccharify sage star ch, the isomaltose thus produced was found to enhance glucose consumpt ion by the cells, resulting in increased volumetric PHA productivity. On the other hand, treatment with a mixture of glucoamylase and pullul anase during the saccharification of sage starch resulted in the produ ction of glucose but no isomaltose. Using this solution, glucose consu mption by R. sphaeroides was lower than that using the solution treate d with alpha-amylase + glucoamylase. These results suggested that isom altose (with 1-6 bonding) contributed to the enhancement of the glucos e consumption rate and PHA yield. This was experimentally confirmed by cultivating R. sphaeroides in a medium containing glucose with either isomaltose or malto-oligosaccharides without 1-6 bonding.