TAXONOMIC IDENTIFICATION OF STREPTOMYCES-EXFOLIATUS K10 AND CHARACTERIZATION OF ITS POLY(3-HYDROXYBUTYRATE) DEPOLYMERASE GENE

The poly(3-hydroxyalkanoate) (PHA) degrading isolate K10 was identifie d as Streptomyces exfoliatus. This bacterium is distinguished from oth er PHA-degrading strains by its ability to utilize both poly(3-hydroxy butyrate) (PHB) and poly(3-hydroxyoctanoate) (PHO). A PHA depolymerase structural gene of S. exfoliatus (phaZ(Sex)) was cloned, expressed an d partially purified from recombinant Escherichia coli. The depolymera se was specific for PHB and did not hydrolyze PHO. This indicated the presence of at least one additional gene in S. exfoliatus which encode s a PHO depolymerase. 3-Hydroxybutyrate was identified as the only pro duct of PHB hydrolysis. Comparison of the DNA-deduced amino acid seque nce revealed high homology to the PHB depolymerase of Comamonas sp. an d low to medium homologies to other PHA depolymerases. The PHB depolym erases of S. exfoliatus and Comamonas sp. represent a subgroup within the family of PHA(SCL) depolymerases. To our knowledge, the S. exfolia tus PHB depolymerase is the first briefly characterized PHA depolymera se of a Gram-positive.