Cloning of the Alcaligenes latus polyhydroxyalkanoate biosynthesis genes and use of these genes for enhanced production of poly(3-hydroxybutyrate) inEscherichia coli

Polyhydroxyalkanoates (PHAs) are microbial polyesters that can be used as c ompletely biodegradable polymers, but the high production cost prevents the ir use in a wide range of applications. Recombinant Escherichia coli strain s harboring the Ralstonia eutropha PHA biosynthesis genes have been reporte d to have several advantages as PHA producers compared with wild-type PHA-p roducing bacteria. However, the PHA productivity (amount of PHA produced pe r unit volume per unit time) obtained with these recombinant E. coli strain s has been lower than that obtained with the wild-type bacterium Alcaligene s latus. To endow the potentially superior PHA biosynthetic machinery to E. coli, we cloned the PHA biosynthesis genes from A. latus. The three PHA bi osynthesis genes formed an operon with the order PHA synthase, beta-ketothi olase, and reductase genes and were constitutively expressed from the natur al promoter in E. call. Recombinant E. call strains harboring the A. latus PHA biosynthesis genes accumulated poly(3-hydroxybutyrate) (PHB), a model P HA product, more efficiently than those harboring the R. eutropha genes. Wi th a pH-stat fed-batch culture of recombinant E. call harboring a stable pl asmid containing the A. latus PHA biosynthesis genes, final cell and PHB co ncentrations of 194.1 and 141.6 g/liter, respectively, were obtained, resul ting in a high productivity of 4.63 g of PHB/liter/h. This improvement shou ld allow recombinant E. coli to be used for the production of PHB with a hi gh level of economic competitiveness.