Cloning of the Alcaligenes latus Polyhydroxyalkanoate Biosynthesis Genes and Use of These Genes for Enhanced Production of Poly(3-hydroxybutyrate) in Escherichia coli

Abstract

ABSTRACTPolyhydroxyalkanoates (PHAs) are microbial polyesters that can be used as completely biodegradable polymers, but the high production cost prevents their use in a wide range of applications. RecombinantEscherichia colistrains harboring theRalstonia eutrophaPHA biosynthesis genes have been reported to have several advantages as PHA producers compared with wild-type PHA-producing bacteria. However, the PHA productivity (amount of PHA produced per unit volume per unit time) obtained with these recombinantE. colistrains has been lower than that obtained with the wild-type bacteriumAlcaligenes latus. To endow the potentially superior PHA biosynthetic machinery toE. coli, we cloned the PHA biosynthesis genes fromA. latus. The three PHA biosynthesis genes formed an operon with the order PHA synthase, β-ketothiolase, and reductase genes and were constitutively expressed from the natural promoter inE. coli. RecombinantE. colistrains harboring theA. latusPHA biosynthesis genes accumulated poly(3-hydroxybutyrate) (PHB), a model PHA product, more efficiently than those harboring theR. eutrophagenes. With a pH-stat fed-batch culture of recombinantE. coliharboring a stable plasmid containing theA. latusPHA biosynthesis genes, final cell and PHB concentrations of 194.1 and 141.6 g/liter, respectively, were obtained, resulting in a high productivity of 4.63 g of PHB/liter/h. This improvement should allow recombinantE. colito be used for the production of PHB with a high level of economic competitiveness.