Taxonomic identification of Streptomyces exfoliatus K10 and characterization of its poly(3-hydroxybutyrate) depolymerase gene.

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